Kurzgesagt – In a Nutshell
Kurzgesagt – In a Nutshell
Embedded Files
Sources – Death
Sources – Death
We thank the following experts for their critical reading, feedback and corrections:
– Dr. Lance B. Becker
Feinstein Institutes for Medical Research, Manhasset, USA
– Dr. Peter A. Noble
University of Alabama at Birmingham, USA
– Prof. Dr. med. Ulrich Dirnagl
Charité – Universitätsmedizin Berlin, Germany
Disclaimer: There isn’t one universally correct “death and decay timeline.” How quickly different organs and tissues change after death depends a lot on the temperature, humidity, and other factors. We did our best to bring together several processes that often happen at the same time into one clear narrative. But the timeline shown here shouldn’t be taken as a strict step-by-step sequence. Many of these phenomena overlap and/or happen in parallel.
– Your heart beats one last time, jerks a bit and then… nothing.
Diseases concerning the heart are the leading cause of death. Your heart can stop in different ways, but for the scenario in this video, we assume death from sudden cardiac arrest, which means the heart suddenly stopped beating due to an electrical malfunction.
#World Health Organization. Cardiovascular diseases. Retrieved May 2026
https://www.who.int/health-topics/cardiovascular-diseases#tab=tab_1
Quote: “Cardiovascular diseases (CVDs) are the leading cause of death globally, taking an estimated 17.9 million lives each year. CVDs are a group of disorders of the heart and blood vessels and include coronary heart disease, cerebrovascular disease, rheumatic heart disease and other conditions. More than four out of five CVD deaths are due to heart attacks and strokes, and one third of these deaths occur prematurely in people under 70 years of age.”
#American Heart Association. Heart Attack and Sudden Cardiac Arrest Differences. Retrieved May 2026
Quote: “Sudden cardiac arrest happens suddenly and often without warning. It happens when an electrical failure in the heart causes an irregular heartbeat (arrhythmia). The heart can’t pump blood to the brain, lungs and other organs. This causes a person to lose consciousness and a pulse. The person can die if they don’t receive help within minutes.”
– Your blood goes from roughly 5 km/h to a full stop.
Blood flow in humans occurs at a big range of speeds, depending on the type and size of the blood vessel, whether it is an artery or a vein, and the speed also changes in relation to the heart beat. Here we are referring to typical speeds found in e.g. the abdominal aorta and iliac vessels (100-150 cm/s): 3.6 - 5.4 km/h.
#Elster DA. Questions and Answers in MRI. Expected Velocities. Retrieved May 2026
https://mriquestions.com/expected-velocities.html
Quote: “Normal human peak systolic blood flow velocities vary with age, cardiac output, and anatomic site. At the aortic valve, peak velocities of up to 500 cm/sec may be possible. The ascending aorta has the highest average peak velocities of the major vessels; typical values are 150-175 cm/sec. Flow in the distal aorta and iliac vessels slows to the 100-150 range, whereas peak velocities in the proximal carotid, brachial, and superficial femoral arteries are about 80-110 cm/sec. Intracranially, peak velocities of the middle and anterior cerebral arteries are approximately 40-70 cm/sec, whereas those in the vertebral-basilar system are only 30-50 cm/sec. Venous velocities are generally less than 20 cm/sec. Conversely, in certain pathological conditions such as arteriovenous fistulas, velocities up to 400 cm/sec may be recorded.”
– You are a complex self-organizing society of 30 trillion individual cells.
#Bianconi E, Piovesan A, Facchin F, et al. An estimation of the number of cells in the human body. Ann Hum Biol. 2013
https://www.tandfonline.com/doi/10.3109/03014460.2013.807878
Quote: “Results: A current estimation of human total cell number calculated for a variety of organs and cell types is presented. These partial data correspond to a total number of 3.72 × 10(13).”
#Sender R, Fuchs S, Milo R. Revised Estimates for the Number of Human and Bacteria Cells in the Body. PLoS Biol. 2016
https://pmc.ncbi.nlm.nih.gov/articles/PMC4991899/
Quote: “For human cells, we identify the dominant role of the hematopoietic lineage to the total count (≈90%) and revise past estimates to 3.0·1013 human cells.”
– In a sense death is all about a lack of oxygen, a chemical knife that animal cells use to split sugar molecules to gain the currency of life: chemical energy, bound in ATP.
Here we describe “aerobic respiration”, which is a fundamental process in animals (and other) cells.
#Monash University. The process of aerobic respiration. Retrieved May 2026
https://www.monash.edu/student-academic-success/biology/cellular-respiration/the-process-of-aerobic-respiration
Quote: “Aerobic respiration is the process by which cells convert glucose and oxygen into ATP (energy), carbon dioxide, and water.
The overall reaction can be summarised as:
Glucose + Oxygen → Carbon Dioxide + Water + 30/32 ATP
It occurs in three stages:
Glycolysis (in the cell’s cytoplasm), where glucose is broken down into pyruvate, NADH and 2 ATP;
The Krebs cycle (in the mitochondria), where pyruvate is further processed to produce NADH and FADH2, 2 ATP; and
The electron transport chain (in the inner mitochondrial membrane), where electrons are transferred to produce large amounts of ATP and water.
The breakdown of glucose is most efficient in the presence of oxygen (aerobic respiration) and produces the most ATP, which is essential for powering cellular functions.”
– Your cells each combine millions of sugar and oxygen molecules each second, so your body is built around constantly pulling oxygen from the air, loading it into your blood and distributing it to every cell of your body.
Aerobic respiration can use millions of sugar and oxygen molecules each second in a respiring cell that has access to glucose and oxygen, but the rates vary widely by cell type, workload, and environment. To do the math for our example, we used numbers reported for horse lymphocytes measured in a lab.
#Monash University. The process of aerobic respiration. Retrieved May 2026
https://www.monash.edu/student-academic-success/biology/cellular-respiration/the-process-of-aerobic-respiration
Quote: “Aerobic respiration is the process by which cells convert glucose and oxygen into ATP (energy), carbon dioxide, and water.
The overall reaction can be summarised as:
Glucose + Oxygen → Carbon Dioxide + Water + 30/32 ATP
It occurs in three stages:
Glycolysis (in the cell’s cytoplasm), where glucose is broken down into pyruvate, NADH and 2 ATP;
The Krebs cycle (in the mitochondria), where pyruvate is further processed to produce NADH and FADH2, 2 ATP; and
The electron transport chain (in the inner mitochondrial membrane), where electrons are transferred to produce large amounts of ATP and water.
The breakdown of glucose is most efficient in the presence of oxygen (aerobic respiration) and produces the most ATP, which is essential for powering cellular functions.”
#LAUREN NT. PACHMAN; The Carbohydrate Metabolism and Respiration of Isolated Small Lymphocytes : In Vitro Studies of Normal and Phytohemagglutinin Stimulated Cells. Blood. 1967
Quote: “3. The small lymphocytes consumed glucose at a rate of 1.87 mµmoles/1 x 107 cells/minute, and produced lactic acid at a rate of 2.30 mµmoles/1 x 107 cells/minute.
4. The oxygen consumption of small equine lymphocytes was 1.023 ± .165 mµmoles oxygen 1 x 107 cells/minute, and that of mixed peripheral blood leukocytes, 1.25 ± .07 mµmoles oxygen/1 x 107 cells/minute, as determined, using a Clark oxygen electrode.”
1 mµmol = 1 nmol = 10-9 moles
1 mole = 6.02214076×1023 molecules
Glucose consumption of 107 lymphocytes: 1.87 nmoles = 1.87x10-9 x 6.02214076×1023 = 1.1 x 1015
Per cell per minute: 1.1 x 1015 / 107 = 1.1 x 108
Per cell per second: 1.1 x 108 / 60 = 1,833,333
Here we also describe the basic mechanism of how your lungs and cardiovascular system work together to supply your body with oxygen.
#Rhodes CE, Denault D, Varacallo MA. Physiology, Oxygen Transport. [Updated 2022 Nov 14]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2026
https://www.ncbi.nlm.nih.gov/books/NBK538336/
Quote: “Oxygen is essential for adenosine triphosphate (ATP) generation through oxidative phosphorylation; therefore, it must be reliably delivered to all metabolically active cells in the body.[1][2] In the setting of hypoxia or low blood oxygen levels, irreversible tissue damage can rapidly occur. Hypoxia can result from an impaired oxygen-carrying capacity of the blood (eg, anemia), impaired unloading of oxygen from hemoglobin in target tissues (eg, carbon monoxide toxicity), or from a restriction of blood supply. Blood becomes typically saturated with oxygen after passing through the lungs, which have a vast surface area and a thin epithelial layer that allows for the rapid diffusion of gasses between blood and the environment. Oxygenated blood returns to the heart and is distributed throughout the body by way of the systemic vasculature.
Oxygen is carried in the blood in two forms. Most oxygen in the blood is bound to hemoglobin within red blood cells, while a small amount of oxygen is physically dissolved in the plasma. The regulation of unloading of oxygen from hemoglobin at target tissues is controlled by several factors, including oxygen concentration gradient, temperature, pH, and concentration of the compound 2,3-bisphosphoglycerate. The most critical measures of adequate oxygen transportation are hemoglobin concentration and oxygen saturation; the latter is often measured clinically using pulse oximetry. Understanding oxygen transport informs our understanding of the underlying mechanisms of tissue hypoxia, ischemia, cyanosis, and necrosis and management to improve global hypoxemia.
Issues of Concern
Oxygen transport is fundamental to aerobic respiration and the survival of complex organisms. The lungs, heart, vasculature, and red blood cells play essential roles in oxygen transport. Oxygen-carrying deficiencies or problems with oxygen transport or delivery are common sequelae of medical illness and must be promptly evaluated and corrected to prevent irreversible tissue damage.
Organ Systems Involved
The lungs are the respiratory organs responsible for the exchange of gasses between the bloodstream and the atmosphere.[3] Venous blood entering the lungs typically has a partial pressure (PO) of 40 mm Hg. Upon passing through the alveolar and pulmonary capillaries, oxygen and carbon dioxide are allowed to equilibrate across the blood-air barrier, resulting in carbon dioxide removal from the blood and oxygen absorption. Typically, arterial blood leaving the lungs has a PO of approximately 100 mg Hg.[4] Oxygenated blood is carried through the cardiovascular system to peripheral tissues. In tissues, oxygen diffuses down its concentration gradient from high to low concentrations and is delivered to cells. In the cell, it will act as the terminal electron acceptor in generating adenosine triphosphate through oxidative phosphorylation.”
– This process is so crucial that over 80% of your cells are exclusively devoted to carrying oxygen in an iron cage: Your red blood cells.
#Sender R, Fuchs S, Milo R. Revised Estimates for the Number of Human and Bacteria Cells in the Body. PLoS Biol. 2016
The “iron cage” we refer to here is the hemoglobin inside the red blood cells, which contains four iron atoms.
#Gregory K. Stanford University Chem 32 Virtual Manual. Hemoglobin. Retrieved May 2026
https://web.stanford.edu/~kaleeg/chem32/hemo/
Quote: “There has to be a biological mechanism for capturing oxygen as O2 (in its high-energy, zero oxidation state) and bringing it to a place where it can be turned into H2O (this is a reduction reaction) in such a way that the energy released by this process can be profitably used by the organism. This is accomplished in most organisms via hemoglobin and/or myoglobin, which are often referred to as oxygen carrier proteins. An iron atom in the center of myoglobin binds to O2 and takes to where the energy is needed. Hemoglobin works almost exactly the same way except that where myoglobin has only one iron-containing protein subunit, hemoglobin has four.”
#Frimat, M.; Boudhabhay, I.; Roumenina, L.T. Hemolysis Derived Products Toxicity and Endothelium: Model of the Second Hit. Toxins. 2019
– And this is why the death cascade usually begins with your brain, heart or lungs. If your lungs fail, oxygen can’t be harvested.
If the lungs fail to breath in enough air to supply the body with oxygen it is called “(acute or chronic) respiratory failure”. If your lungs stop breathing completely for whatever reason (accident/drowning, a disease, etc.), and it remains untreated, it is always fatal.
#National Heart, Lung, and Blood Institute. What Is Respiratory Failure? Retrieved May 2026
https://www.nhlbi.nih.gov/health/respiratory-failure
Quote: “Respiratory failure is a serious condition that makes it difficult to breathe on your own. Respiratory failure develops when the lungs can’t get enough oxygen into the blood.
We breathe oxygen from the air into our lungs, and we breathe out carbon dioxide, which is a waste gas made in the body’s cells. Breathing is essential to life itself. Oxygen must pass from our lungs into our blood for our tissues and organs to work properly.
Buildup of carbon dioxide can damage tissues and organs and prevent or slow oxygen delivery to the body.
Acute respiratory failure happens quickly and without much warning. It is often caused by a disease or injury that affects your breathing, such as pneumonia, opioid overdose, stroke, or a lung or spinal cord injury
Respiratory failure can also develop slowly. When it does, it is called chronic respiratory failure. Symptoms include shortness of breath or feeling like you can’t get enough air, extreme tiredness, an inability to exercise as you did before, and sleepiness.
A doctor may diagnose you with respiratory failure based on the oxygen and carbon dioxide levels in your blood, a physical exam to see how fast and shallow your breathing is and how hard you are working to breathe, as well as the results of lung function tests.
If you are diagnosed with a serious lung disease such as respiratory failure, you may need extra oxygen through tubes in your nose or support with a breathing machine called a ventilator.”
#Universitätsspital Zürich. Acute respiratory failure. Retrieved May 2026
https://www.usz.ch/en/disease/acute-respiratory-failure/
Quote: “Acute respiratory failure
ARDS, Acute Respiratory Distress Syndrome
Acute respiratory failure is life-threatening and we must treat it immediately. Otherwise there is a risk of serious complications such as multiple organ failure or death.
There are several causes of “Acute Respiratory Distress Syndrome” – ARDS for short. Examples include pneumonia and blood poisoning, but also the inhalation of smoke, toxic fumes or water. Acute lung failure can be recognized by symptoms such as shortness of breath, rapid breathing, an accelerated heartbeat and a blue discoloration of the skin due to the lack of oxygen. Doctors have to give artificial respiration to many patients with ARDS in order to save their lives.
What is acute respiratory failure?
Acute respiratory failure is a life-threatening condition and always a case for intensive care. The lungs are so severely damaged that fluid accumulates there and their function deteriorates considerably. As a result, organs and tissues no longer receive enough oxygen and nutrients. Without immediate treatment, acute respiratory failure is often fatal. The lung disease has many other names: Acute respiratory distress syndrome, shock lung, adult respiratory distress syndrome or in English “Acute Respiratory Distress Syndrome”, abbreviated ARDS.
The causes of acute respiratory failure can be diseases such as pneumonia. However, inhalation of smoke and toxic gases as well as injuries to the lungs caused by an accident are also possible causes. The symptoms of ARDS are shortness of breath, rapid breathing and an accelerated heartbeat. Patients feel increasingly exhausted and their skin turns bluish. Eventually, the respiratory distress becomes more and more severe until artificial respiration is often necessary. It ensures the oxygen supply and improves the chances of survival.
Doctors always treat the cause of the acute respiratory failure, for example pneumonia. In addition, there are other supportive therapies, such as painkillers, circulation-stabilizing medication or blood thinners. Despite intensive treatment, ARDS is associated with a high mortality rate.”
– If your heart fails, it can’t be distributed.
Your heart can “fail” in different ways: For example it can beat irregularly, making blood flow inefficient or insufficient; a vessel can be blocked, so the heart still beats but it cannot move blood anymore; or it can stop beating completely due to e.g. a failure in the electrical signalling. In any case, your heart failing to pump blood is fatal within minutes if not treated.
#LifeSource. What Is Clinical Death? 2023
https://www.life-source.org/latest/what-is-clinical-death/
Quote: “Clinical death is a term that describes the cessation (stopping) of a patient’s heart pumping blood through the body and, inevitably, is paired with a lack of breathing. Clinical death is a medical emergency, without immediate intervention, the window to reverse the condition will close, and legal death will be declared.”
#Cleveland Clinic. Cardiac Arrest. Retrieved May 2026
https://my.clevelandclinic.org/health/diseases/21736-cardiac-arrest
Quote: “Abnormal electrical signals cause cardiac arrest, while a blocked artery causes a heart attack.
Cardiac arrest is an electrical problem with your heart. A heart attack is a circulation problem.
Cardiac arrest happens when your heart stops beating or beats so fast that it stops pumping blood. When your heart isn’t pumping blood, this puts your organs and whole body at risk of death within minutes because they need a constant supply of oxygen. Your blood delivers that oxygen.
With this condition, people typically collapse and can’t respond. Symptoms start without warning. This is why people also call this life-threatening condition sudden cardiac arrest.
Cardiac arrest (an electrical failure) isn’t the same as a heart attack. A heart attack happens when a blocked artery cuts off blood flow to heart muscle.
With cardiac arrest, your heart stops beating, but a rescue is still possible. With immediate treatment, you can survive. If someone doesn’t save you, it leads to sudden cardiac death.”
– And if your brain fails, neither can continue working.
When the brain fails to send signals, neither the heart nor the lungs can sustain their function, and will soon stop to beat / breathe (within minutes). After brain death, patients can only be kept alive by artificially supporting them in a hospital setting (pace maker; ventilator etc.). Brain death is considered legal death, but the details vary a bit between countries.
#National Health Service. Brain death. Retrieved May 2026
https://www.nhs.uk/conditions/brain-death/
Quote: “Brain death (also known as brain stem death) is when a person on an artificial life support machine no longer has any brain functions. This means they will not regain consciousness or be able to breathe without support.
A person who is brain dead is legally confirmed as dead. They have no chance of recovery because their body is unable to survive without artificial life support.
Brain death is legal death
If someone is brain dead, the damage is irreversible and, according to UK law, the person has died. It can be confusing to be told someone has brain death, because their life support machine will keep their heart beating and their chest will still rise and fall with every breath from the ventilator. But they will not ever regain consciousness or start breathing on their own again. They have already died.
The brain stem
The brain stem is the lower part of the brain that's connected to the spinal cord (part of the central nervous system in the spinal column). The brain stem is responsible for regulating most of the body's automatic functions that are essential for life.
These include:
breathing
heartbeat
blood pressure
swallowing
The brain stem also relays information to and from the brain to the rest of the body, so it plays an important role in the brain's core functions, such as consciousness, awareness and movement. After brain death, it is not possible for someone to remain conscious.
Causes of brain death. Brain death can happen when the blood or oxygen supply to the brain is stopped. This can be caused by:
cardiac arrest – when the heart stops beating and the brain is starved of oxygen
a heart attack – when the blood supply to the heart is suddenly blocked
a stroke – when the blood supply to the brain is blocked or interrupted
a blood clot – a blockage in a blood vessel that disturbs or blocks the flow of blood around your body
Brain death can also be caused by:
a severe head injury
a brain haemorrhage
infections, such as encephalitis
a brain tumour
Brain death is different from a vegetative state
The difference between brain death and a vegetative state (a disorder of consciousness), which can happen after extensive brain damage, is that it's possible to recover from a vegetative state, but brain death is permanent.”
– Wherever death starts, your brain is usually the first part of your body that dies.
#Sandroni C, Cronberg T, Sekhon M. Brain injury after cardiac arrest: pathophysiology, treatment, and prognosis. Intensive Care Med. 2021
https://pmc.ncbi.nlm.nih.gov/articles/PMC8548866/
Quote: “Cardiac arrest results in cessation of both cardiac output and oxygen delivery to all vital organs. This no-flow phase starts upon the onset of cardiac arrest and lasts until partial reperfusion is established by cardiopulmonary resuscitation (CPR).
Despite accounting for only 2% of body weight, the brain receives 15–20% of total cardiac output to maintain tissue homeostasis [4]. Brain tissue viability strongly depends on consistent supply of oxygen and energy substrates, namely glucose, and cessation of cerebral blood flow (CBF) results in an immediate interruption of brain activity. Human studies demonstrate that consciousness is lost between 4 and 10 s of absent CBF [5], while the electroencephalogram (EEG) becomes isoelectric after 10–30 s of asystole [6].”
– It is your most oxygen and energy hungry organ, running quadrillions of operations each second.
#Padamsey Z, Rochefort NL. Paying the brain's energy bill. Curr Opin Neurobiol. 2023
https://www.sciencedirect.com/science/article/pii/S0959438822001623
Quote: “The brain is metabolically expensive. In humans, the brain consumes approximately 20% of our metabolic energy, despite comprising only 2% of our body mass, making it amongst the most energetically costly organs in the body (Figure 1a) [1,2].
Figure 1. The brain is energetically expensive given its mass. Depicted are pie charts showing the relative mass (left; % of total body mass) and relative levels of resting energy consumption (right; % of total energy consumption at rest) of various organs in the human body. The brain's relative mass and resting energy expenditure are depicted in blue. (Data from Ref. [1], brain image from doi.org/10.5281/zenodo.3925989).”
#Sekhon, M.S., Ainslie, P.N. & Griesdale, D.E. Clinical pathophysiology of hypoxic ischemic brain injury after cardiac arrest: a “two-hit” model. Crit Care (2017)
https://link.springer.com/article/10.1186/s13054-017-1670-9
Quote: “During CA, cessation of CDO2 occurs with resultant neuron ischemia and cell death within minutes [9] (Fig. 1). The cerebrum consumes 20% to 25% of cardiac output to maintain function [3]. The brain is devoid of nutrient stores, and consequently neuroglycopenia and metabolic crisis occur within minutes after CA [10], leading to cell death.”
It is near impossible to quantify how many operations the human brain conducts every second, also because it is not clear how exactly to define an “operation”. But if we use the number of binding events of neurotransmitters to synapses, estimates are around 1019 (ten quintillion) events per second. If we assume this is somewhat inflated/too high, the real number is likely still in the range of quadrillions or more (one quadrillion = 0.001 quintillion).
#Lloyd, Seth, and Michele Reilly. “Natural Intelligence: The Information Processing Power of Life.” arXiv (2025)
https://arxiv.org/pdf/2506.16478
Quote: “It is salutary to compare the amount of information processing going on in all of our cells, with the amount of information processing in the brain. There are different ways of estimating the amount of information processing in the brain: in the spirit of defining a bio-op as the formation or breaking of a chemical bond, we define a neural bio-op to be the release or binding of a neurotransmitter molecule to a receptor during the firing of a synapse. The brain has around 1011 neurons, with an average firing rate of around 10 times per second. Each neuron has on the order of 103 synapses, each of which releases on the order of 104 neurotransmitter molecules when the neuron fires. The synaptic binding energy is on the order of half an electron volt per neurotransmitter. If we measure the total number of bio-ops in the neural dynamics in terms of the number of synaptic binding events per second, we obtain around 1019 bio-ops per second in the operation of the brain [8]. (If we count only the information contained in neural spike trains, we obtain a few tera-ops per second.)”
– Less than 30 seconds after your heart stops, the electrical communication between the different parts of your brain begins to fade. You think your last conscious thought and faint.
The time it takes for loss of consciousness to set in when the brain is deprived of oxygen depends a lot on the individual person and the environmental circumstances. Some sources report a loss of consciousness as early as 4 seconds, some after a much longer time. We go with a rather conservative 30 seconds here, because a meta-analysis supports a typical loss of consciousness “within 30 seconds”.
#Pana R, Hornby L, Shemie SD, Dhanani S, Teitelbaum J. Time to loss of brain function and activity during circulatory arrest. J Crit Care. 2016
https://www.sciencedirect.com/science/article/abs/pii/S0883944116300259?via%3Dihub
Quote: “Most studies show that clinical loss of consciousness and loss of EEG activity occur within 30 seconds after abrupt circulatory arrest and may occur before circulatory arrest after progressive hypoxia-ischemia. Prospective clinical studies are required to confirm these observations.”
#Sekhon, M.S., Ainslie, P.N. & Griesdale, D.E. Clinical pathophysiology of hypoxic ischemic brain injury after cardiac arrest: a “two-hit” model. Crit Care (2017).
https://link.springer.com/article/10.1186/s13054-017-1670-9
Quote: “Clinically, loss of neurologic function is manifested by a decreased level of consciousness after global cerebral ischemia. Historically, Rossen et al. demonstrated that cessation of cerebral blood flow (CBF) by neck cuff insufflation to 600 mmHg in humans precipitated acute decreased level of consciousness within 10 seconds [16]. Decreased level of consciousness after CA occurs within 20 seconds after onset of ventricular fibrillation [17]. Loss of neurologic function has been demonstrated by isoelectric electroencephalography in observational studies [16]. Pana et al. identified human studies demonstrating isoelectric electroencephalography rhythms within 15 seconds and 30 seconds of asystole and ventricular fibrillation, respectively [16]. These findings are corroborated by animal studies establishing a similar timeline of 10 to 30 seconds from the onset of cerebral ischemia to isoelectric electroencephalography [18].”
#Sandroni C, Cronberg T, Sekhon M. Brain injury after cardiac arrest: pathophysiology, treatment, and prognosis. Intensive Care Med. 2021
https://pmc.ncbi.nlm.nih.gov/articles/PMC8548866/
Quote: “Cardiac arrest results in cessation of both cardiac output and oxygen delivery to all vital organs. This no-flow phase starts upon the onset of cardiac arrest and lasts until partial reperfusion is established by cardiopulmonary resuscitation (CPR).
Despite accounting for only 2% of body weight, the brain receives 15–20% of total cardiac output to maintain tissue homeostasis [4]. Brain tissue viability strongly depends on consistent supply of oxygen and energy substrates, namely glucose, and cessation of cerebral blood flow (CBF) results in an immediate interruption of brain activity. Human studies demonstrate that consciousness is lost between 4 and 10 s of absent CBF [5], while the electroencephalogram (EEG) becomes isoelectric after 10–30 s of asystole [6].”
– Neurons are biological electrical wires with almost no sugar storage and especially vulnerable to a lack of energy.
#Sandroni C, Cronberg T, Sekhon M. Brain injury after cardiac arrest: pathophysiology, treatment, and prognosis. Intensive Care Med. 2021
https://pmc.ncbi.nlm.nih.gov/articles/PMC8548866/
Quote: “Despite accounting for only 2% of body weight, the brain receives 15–20% of total cardiac output to maintain tissue homeostasis [4]. Brain tissue viability strongly depends on consistent supply of oxygen and energy substrates, namely glucose, and cessation of cerebral blood flow (CBF) results in an immediate interruption of brain activity. Human studies demonstrate that consciousness is lost between 4 and 10 s of absent CBF [5], while the electroencephalogram (EEG) becomes isoelectric after 10–30 s of asystole [6].
Due to their lack of inherent energy stores, neurons are particularly vulnerable to ischaemia and cellular damage starts immediately upon absence of CBF. At the cellular level, ischaemia results in cessation of aerobic metabolism with consequent depletion of high-energy substrate adenosine triphosphate (ATP) [3] (Fig. 1). ATP depletion results in dysfunctional energy-dependent Na+/K+ ion exchange pump action, which leads to massive influx of sodium and water and intracellular cytotoxic oedema. Potassium efflux and membrane depolarisation also ensue shortly thereafter, leading to the opening of voltage-sensitive Ca++ channels and intracellular Ca++ influx. Experimental evidence shows that signs of brain oedema on MRI develop already during cardiac arrest and resuscitation [7].”
#Sekhon, M.S., Ainslie, P.N. & Griesdale, D.E. Clinical pathophysiology of hypoxic ischemic brain injury after cardiac arrest: a “two-hit” model. Crit Care (2017).
https://link.springer.com/article/10.1186/s13054-017-1670-9
Quote: “During CA, cessation of CDO2 occurs with resultant neuron ischemia and cell death within minutes [9] (Fig. 1). The cerebrum consumes 20% to 25% of cardiac output to maintain function [3]. The brain is devoid of nutrient stores, and consequently neuroglycopenia and metabolic crisis occur within minutes after CA [10], leading to cell death.”
#Onkar, A., Sheshadri, D., & Ganesh, S. Glycogen: the missing link in neuronal autophagy? Autophagy (2020)
https://www.tandfonline.com/doi/full/10.1080/15548627.2020.1802090
Quote: “Glycogen − a polymer of glucose − is the primary energy reserve in the animal kingdom. The synthesis and degradation of glycogen are regulated by a dedicated set of enzymes (GYS [glycogen synthase] and PYG [glycogen phosphorylase], respectively), depending upon the physiology and energy needs of the body. The liver and the muscle are the two principle glycogen storage sites in mammals, although small amounts of glycogen are stored in almost all cell types. Until recently, it was thought that healthy neurons do not synthesize or store glycogen [Citation1], and they mostly depend on the astrocytic glycogen reserves for neuronal energy and function (astrocyte-neuron-lactate shuttle hypothesis) [Citation2]. However, recent studies demonstrate that cultured neurons do contain a low but measurable amount of glycogen, and that the key enzymes – GYS and PYG – are active under basal conditions [Citation3].”
– Like all cells, they are bags of molecules and water, separated by a delicate membrane from their surroundings. This membrane is an extremely active, hi-tech molecular machine. Constantly monitoring and guiding millions of molecules inside and outside, maintaining a fragile balance, which needs loads of energy.
Neurons “fire” by rapidly moving ions across their membrane to generate an electrical current across their membrane. However, even “at rest”, when the net transfer is zero and the neuron is not firing, the membranes still shift millions of molecules (or ions, to be more precise) from outside to inside and vice versa. Moving these molecules via channels in the membrane costs energy in the form of ATP.
#Science Direct. Nerve Cell Membrane. Retrieved May 2026
https://www.sciencedirect.com/topics/neuroscience/nerve-cell-membrane
Quote: “The nerve cell membrane is composed of a lipid bilayer that has hydrophilic (water loving) and hydrophobic ends. When placed in an aqueous medium, the phospholipids arrange themselves so that the hydrophilic ends are facing outwards and the hydrophobic ends are inside. This leads to an ionic separation across the nerve axon that results in a charge separation. Although there are a number of charged proteins, the electrical gradients are mostly due to the difference in concentrations between sodium (Na+) and potassium (K+) ions. Minute changes in these concentrations lead to a change in the membrane potential, even though there is relatively little actual ion flow.
Various membrane channels consist of proteins embedded in the phospholipid bilayer that have a neutral charge and allow the passive flow of charged ions. There are separate channels for Na+, K+, and calcium (Ca+2) ions. The interior of the axon has a charge of approximately -90 millivolts (mV), with a relatively greater concentration of K+ ions with respect to the outside. There is a passive leak of K+ ions out and Na+ ions in, which causes the interior of the axon to become less negative with regard to the outside. There is an ATP dependent Na+/K+ pump which imports K+ and exports Na+ in a ratio of two K+ for every three Na+. This maintains the normal resting membrane potential, and prevents spontaneous depolarization. Since maintaining the ionic charge separation across the membrane requires energy, this mechanism stops when the energy supply is interrupted.”
For a “leak” current, 100 pA (= 10-10) Ampere is roughly realistic:
#Spikes and Bursts. Patch-clamp data analysis in Clampfit: passive membrane properties. Retrieved May 2026
https://spikesandbursts.wordpress.com/2022/05/13/patch-clamp-analysis-clampfit-passive-properties/
Quote: “For your own recordings, it is important to establish clear inclusion criteria for analysis. Quality criteria standards in whole-cell patch clamp usually include, among others, the formation of a gigaseal (>1 GΩ), stable access resistance <20-25 MΩ, leak current within +/- 100 pA, voltage difference before and after sweeps <2-3 mV. These values will partially depend on the experiment, cell type, and brain sample. See the methods section of Gouwens et al., 2019 for reference.”
100 pA Charge of single electron / monovalent ion (like N+,K+): q = 1.6×10−19 C
#Britannica Editors. "electron charge." Encyclopedia Britannica, March 7, 2025.
https://www.britannica.com/science/electron-charge
Quote: “electron charge, (symbol e), fundamental physical constant expressing the naturally occurring unit of electric charge, equal to 1.602176634 × 10−19 coulomb.”
I (current) = Q (total charge) / t (time)
Q = N (ions flowing per second) x q (charge per ion)
Rearrange: N = I / q
N = 10−10 / 1.6x10−19 = 6.25x108 = 625 million
– As soon as a neuron gets low on energy it starts shutting down non essential processes.
When ATP runs low in neurons, AMPK, an energy sensor activated by ATP depletion, shifts the neuron’s metabolism to conserve ATP and protect the cell from damage.
#Zhang J, Wang S, Zhang H, Yang Y, Yuan M, Yang X, Wen Y. The role of the AMPK/ERK1/2 signaling pathway in neuronal oxidative stress damage following cerebral ischemia-reperfusion. Tissue Cell. 2024
https://www.sciencedirect.com/science/article/pii/S0040816624001733
Quote: “During ischemia, intracellular ATP levels decrease while the AMP/ATP ratio increases, leading to the activation of AMPK (Lee et al., 2020). Numerous studies have shown that activated AMPK helps maintain cellular energy homeostasis and alleviate cellular damage by inhibiting protein synthesis, promoting glucose uptake and metabolism, and enhancing mitochondrial function (Cai et al., 2022; Wang et al., 2022).”
– But as its reserves run out the membrane stops working and the outside invades: Water and salt ions begin to diffuse in, causing the cell to swell. This is bad.
#Sandroni C, Cronberg T, Sekhon M. Brain injury after cardiac arrest: pathophysiology, treatment, and prognosis. Intensive Care Med. 2021
https://pmc.ncbi.nlm.nih.gov/articles/PMC8548866/
Quote: “Due to their lack of inherent energy stores, neurons are particularly vulnerable to ischaemia and cellular damage starts immediately upon absence of CBF. At the cellular level, ischaemia results in cessation of aerobic metabolism with consequent depletion of high-energy substrate adenosine triphosphate (ATP) [3] (Fig. 1). ATP depletion results in dysfunctional energy-dependent Na+/K+ ion exchange pump action, which leads to massive influx of sodium and water and intracellular cytotoxic oedema. Potassium efflux and membrane depolarisation also ensue shortly thereafter, leading to the opening of voltage-sensitive Ca++ channels and intracellular Ca++ influx. Experimental evidence shows that signs of brain oedema on MRI develop already during cardiac arrest and resuscitation [7].”
Sekhon, M.S., Ainslie, P.N. & Griesdale, D.E. Clinical pathophysiology of hypoxic ischemic brain injury after cardiac arrest: a “two-hit” model. Crit Care (2017).
https://link.springer.com/article/10.1186/s13054-017-1670-9
Quote: “As CDO2 decreases, adenosine triphosphate production halts, causing cessation of energy-dependent ion channel function [11]. Subsequent intracellular Na+ accumulation results in cytotoxic edema. Depletion of adenosine triphosphate leads to anaerobic metabolism, cerebral lactate accumulation, and intracellular acidosis [12]. Additionally, cellular ischemia causes intracellular Ca2+ influx through N-methyl-d-aspartate channels, which activates lytic enzymes [13] and mitochondrial dysfunction, thereby depleting adenosine triphosphate further [14]. Finally, excitatory neurotransmitter release activates lipases and proteases, which leads to apoptosis [15].”
– Neurons’ membranes actively balance out different ions to maintain a potential of literal electricity that they use to send and receive orders. When too many ions rush in, the electrical balance collapses – the neuron goes dark. As the membrane fails, the neuron spills ions onto its neighbors, causing their electricity to fail, and they go dark, too.
But it gets even worse. The dysfunctional membrane starts absorbing massive amounts of the most dangerous ion of all: calcium. Useful in small doses, it now turns into a killer. Inside the neuron, it activates enzymes that break down vital cellular structures, damaging it beyond repair.
The failing cell goes into panic mode and vomits neurotransmitters onto its neighbors. They have a double effect: they scream at other neurons to get more excited, forcing them into electrical overdrive, speeding up their eventual collapse. And they order them to take up even more calcium. Normally this is part of their regular signalling, but now it only makes things worse. A deadly chain reaction is unleashed: dying neurons destabilize their neighbors, spreading electrical failure and death.
Here we describe the basics of what happens in the brain when oxygen runs out, as per “Excitotoxicity” / “Spreading Depolarization” theory. They are two closely related theories on how neuron death spreads in severe brain injury. We mostly represent Spreading Depolarization theory. The details are not yet fully understood, and much of what is known comes from animal experiments. The role of the neurotransmitter glutamate is especially contested.
#Charité – Universitätsmedizin Berlin. Braintsunamis – Spreading depolarization and spreading ischemia. Retrieved May 2026
https://www.charite-academy.de/spreading-depolarization-and-spreading-ischemia/
Quote: “Spreading depolarization is the sudden, near-complete but potentially reversible breakdown of the physiological ion concentration gradients across neuronal cell membranes. It occurs under pathological conditions such as intoxication with chemicals (e.g. potassium), pharmacological inhibition of the sodium-potassium pump (Na/K-ATPase) or the respiratory chain, or during hypoxia, hypoglycemia, brain trauma or stroke. A complete breakdown of the neuronal ion gradients does not exist in the living brain because neuronal membranes will lyse and the neurons will die beforehand.
Spreading depolarization occurs when neuronal cation outflux by the ATP-dependent Na/K-ATPase pumps locally fails to compensate for cation influx of sodium and calcium. Cells experience an abrupt sodium and calcium overload and a loss of potassium. Water follows sodium and calcium ions entering the intracellular space because these outnumber the potassium ions leaving the cells. The near-complete ionic breakdown and water movement into the cells inevitably lead to cytotoxic edema with swelling of the cellular soma and distortion of the dendritic spines (see Fig. 1: Mechanism of spreading depolarization).
Signaling overload of the system in relation to the normal membrane Na/K-ATPase pump activity can cause a temporary, relatively harmless spreading depolarization. In this case, additional pump activity is recruited to re-establish the normal steady state before any tissue damage occurs. This recruitment will only take about one minute, but even then, tissue ATP will fall transiently by about 50%.
In the event of a breakdown of the Na/K-ATPase function, however, the additional recruitment of pumps cannot re-establish the normal steady state. This situation is critical: the ionic breakdown will persist and will interfere in many ways with the structural metabolism of the neurons. If the cells remain in this non-physiological state for too long, they will eventually die. In animals, neurons can die within this state, or they can show a transient electrical recovery after prolonged metabolic compromise and then die later on. How long neurons tolerate this pathological condition presumably depends on the type of neuron, the developmental state and the initial damage that led to the ionic breakdown.
Figure 1. A Under physiological conditions, low intracellular sodium concentration and high intracellular levels of potassium maintain a membrane potential of -70mV. While there is a constant flux of ions across the cell membrane through ion-specific open non-gated channels, the Na/K-ATPase helps maintain the cells resting potential by hydrolysing one molecule of ATP to move 3 sodium ions out of the cell with each cycle, and 2 potassium ions into the cell with each cycle. [...] B The core process of spreading depolarization is the failure of the Na/K-ATPase to provide sufficient outward currents to balance the persistent inward currents. This results in loss of electrochemical activity, almost passive ion distribution across the cellular membranes (breakdown of ion concentration gradients), intracellular hyperosmolality with cellular swelling and distortion of dendritic spines (cytotoxic edema), and extracellular hyposmolality with shrinkage of the extracellular space from 20% to 5%. Neuronal membrane potential during spreading depolarization approaches zero.“
#Andrew, R.D., Hartings, J.A., Ayata, C. et al. The Critical Role of Spreading Depolarizations in Early Brain Injury: Consensus and Contention. Neurocrit Care (2022).
https://link.springer.com/article/10.1007/s12028-021-01431-w
Quote: “At the immediate onset of brain ischemia, spreading depolarization (SD) is the principal mechanism of electrochemical membrane failure and neuronal swelling in gray matter of the higher brain [1,2,3,4,5,6]. In this review, the “higher” brain includes all structures above the hypothalamus and brainstem. Within 1–2 min of severe ischemia, depletion of the available ATP pool leads to Na+/K+ pump failure with eruption of a front of cellular depolarization that propagates at 1–9 mm/minute throughout the ischemic tissue as well as into the surrounding penumbral and normal tissue [7,8,9,10,11]. This SD wave drives a sudden and active jump in neuronal membrane potential to near 0 mV over seconds (Fig. 1), in contrast to most other tissues of the body that slowly depolarize over many minutes in an energy crisis. However, SD does not arise only in ischemic tissue but can also be provoked by various noxious electrical, chemical, thermal, or mechanical disturbances of gray matter. Thus, SD is associated with a range of diseases and conditions, including migraine-associated aura, concussion [12], traumatic brain injury (TBI), subarachnoid hemorrhage, intracerebral hemorrhage, ischemic stroke, circulatory arrest (Fig. 2), brain death prior to circulatory collapse, and sudden unexplained death in epilepsy [3, 13,14,15,16,17,18]. When SD invades tissue that has not already been rendered electrically silent by the triggering pathology, SD induces a loss of spontaneous and evoked activity termed “spreading depression” [19].”
#Dreier, J.P., Major, S., Foreman, B., Winkler, M.K.L., Kang, E.-J., Milakara, D., Lemale, C.L., DiNapoli, V., Hinzman, J.M., Woitzik, J., Andaluz, N., Carlson, A. and Hartings, J.A. Terminal spreading depolarization and electrical silence in death of human cerebral cortex. Ann Neurol. (2018)
https://onlinelibrary.wiley.com/doi/epdf/10.1002/ana.25147
Quote: “In animals, complete global ischemia causes com-plete electrical inactivity (ie, isoelectricity) of affected gray matter within about 20 to 40 seconds. 7 This cere-bral silencing is regarded as an austerity program to curbneuronal energy usage by the shutdown of nonessentialcell functions well before the neuronal adenosine triphos-phate (ATP) pool is depleted and prospects of tissue recovery vanish. 4,8 Accordingly, the electrical inactivity corresponds to a hyperpolarization of neurons, 9 which may be mediated by several mechanisms, as reviewed recently.10 A hallmark of electrical silencing after onset of severe ischemia is its simultaneous development in affected tissue, which has been termed “nonspreadingdepression.”11 Despite this austerity program, sodium and calcium always leak into cells and potassium leaks out. These movements are driven by the release of Gibbsfree energy. Eventually, ATP is depleted and the Na,K-ATPase fails to restore the leaking ions. When a thresh-old level of failure, usually reached 1 to 5 minutes afternoon spreading depression, has rendered the ischemic tissue isoelectric, neurons then undergo abrupt, nonlinear run-down in the ion gradients across the cellular membranes.This depolarization develops en masse from either one or multiple foci and spreads in the tissue as a self-propagating wave. 7,9,12–14 Initially termed “anoxic” or“asphyxial” depolarization,15 this spreading depolarization(SD) initiates a plethora of toxic changes, including intracellular calcium and sodium loading, steep rise in extracellular glutamate, and cytotoxic edema, as reviewedrecently.16–18 Importantly, cellular injury does notdevelop during the initial period of nonspreading depres-sion, but only begins with a delay after SD ignition.”
#Andrew RD, Farkas E, Hartings JA, Brennan KC, Herreras O, Müller M, Kirov SA, Ayata C, Ollen-Bittle N, Reiffurth C, Revah O, Robertson RM, Dawson-Scully KD, Ullah G, Dreier JP. Questioning Glutamate Excitotoxicity in Acute Brain Damage: The Importance of Spreading Depolarization. Neurocrit Care. 2022
https://pmc.ncbi.nlm.nih.gov/articles/PMC9259542/
Quote: “SD is the principal mechanism of electrochemical membrane disruption and neuronal swelling [2–5] in gray matter of the higher brain. Severe ischemia depletes the adenosine triphosphate (ATP) pool, leading to Na+/K+ pump failure, which generates a front of cellular depolarization that propagates at 1–9 mm/min through the ischemic gray matter and even into healthy tissue [6–8]. The SD wave is a sudden loss of membrane potential to near-zero millivolts that occurs over seconds. SD can be evoked by various noxious electrical, chemical, thermal, or mechanical disturbances of gray matter that stress the Na+/K+ pump. Thus, SD is associated with a range of diseases and conditions, including migraine-associated aura, concussion, traumatic brain injury (TBI), subarachnoid hemorrhage, intracerebral hemorrhage, ischemic stroke, circulatory arrest, and brain death prior to circulatory collapse [1, 9–14]. SD can also invade gray matter that has not been metabolically compromised, inducing a loss of neuronal activity termed “spreading depression” [15].
In the ischemic core, neurons will die under a maintained depolarization that typically lasts 20–30 min or more [16–19]. However, if the ischemic core is reperfused within ~ 15 min, all neurons will survive, even though persistently depolarized for about 15 min [18, 20]. In contrast, perfusion completely ceases after cardiac arrest, and so neurons start to die after about 5 min [21].”
#Soylu KO, Yemisci M, Karatas H. The link between spreading depolarization and innate immunity in the central nervous system. J Headache Pain. 2025
https://pmc.ncbi.nlm.nih.gov/articles/PMC11792447/
Quote: “SD significantly disrupts the homeostasis of ions and neurotransmitters, leading to substantial transmembrane ionic shifts characterized by sodium (Na+) and calcium (Ca²⁺) influx, accompanied by water movement and K⁺ and glutamate efflux from affected brain cells [51].”
#Belov Kirdajova D, Kriska J, Tureckova J and Anderova M. Ischemia-Triggered Glutamate Excitotoxicity From the Perspective of Glial Cells. Front. Cell. Neurosci. (2020)
https://www.frontiersin.org/journals/cellular-neuroscience/articles/10.3389/fncel.2020.00051/full
Quote: “Figure 1. Ischemic cascade. The relay of extracellular and intracellular processes leading to pathogenic states and eventually to cell death.
[...] A sustained activation of Ca2+-permeable channels due to an impaired glutamate uptake by astrocytes (Mori et al., 2004) leads to a pathological increase in intracellular Ca2+ ([Ca2+]i) and overexcites the cells which in turn release harmful substances, such as reactive oxygen species (ROS; Sattler et al., 1999) or ATPases, endonucleases, proteases, and phospholipases that belong to a group of Ca2+-dependent degradative enzymes. Once the cellular membrane is disrupted by phospholipases, more detrimental chemicals enter the cell, eventually causing the release of apoptotic signals from mitochondria and triggering the caspase-dependent cascade, which leads to the death of cells (Rebai and Amri, 2018; Figure 2).
Figure 2. Excitotoxic events caused by aberrant Ca2+ levels. High concentrations of intracellular Ca2+ lead to the activation of Ca2+-dependent enzymes, such as proteases and nitric oxide synthase (NOS). This results in the dysfunction of mitochondria, oxidative stress, and oxidation of essential macromolecules, all contributing to apoptosis or necrosis.”
#Dreier J, Reiffurth C.The Stroke-Migraine Depolarization Continuum. Neuron. 2015
https://www.cell.com/neuron/fulltext/S0896-6273(15)00333-5
Quote: “At a given tissue spot, the near-complete breakdown in ion gradients during SD happens rapidly, within ∼6–8 s, and lasts locally for at least 30 s. Ion changes of this magnitude never occur under other conditions in living neurons. As an example for the ion concentration changes during SD, in dendrites, the intracellular calcium may surge up to 25 μM, a level which is toxic when the recovery from SD is hindered as in metabolically compromised tissue (Aiba and Shuttleworth, 2012; Dietz et al., 2008). The ion changes lead to intracellular hyperosmolality (Kraig and Nicholson, 1978). The resulting water influx causes cytotoxic edema and shrinkage of the extracellular volume fraction from 20% to ∼5% (Mazel et al., 2002; Vorísek and Syková, 1997; Windmüller et al., 2005). This is observed as swelling of neuronal somata and focal dendritic enlargement and constriction (“beading”) (Murphy et al., 2008; Risher et al., 2009, 2010; Takano et al., 2007) (Box 1). Moreover, neuronal mitochondria depolarize (Bahar et al., 2000), and neurotransmitters such as acetylcholine, γ-aminobutyric acid (GABA), and glutamate are released in large amounts (Fabricius et al., 1993; Zhou et al., 2013). Endogenous GABA may have a janus-faced role as GABAA receptor activation limits the propagation rate (Aiba et al., 2012), but may, on the other hand, facilitate cell swelling through chloride entry (Allen et al., 2004). This contrasts with glutamate, whose primary effect is facilitation.”
#Frank R, Marinesco S, Bari F, Menyhárt Á and Farkas E. Glutamate load fosters spreading depolarization under osmotic stress in brain slices. Front. Cell. Neurosci. (2026)
https://www.frontiersin.org/journals/cellular-neuroscience/articles/10.3389/fncel.2025.1722194/full
Quote: “Introduction: Cerebral edema is a hallmark of lesion progression after acute ischemic stroke (AIS) and a major contributor to the evolution of spreading depolarizations (SDs). SDs trigger extracellular glutamate accumulation and excitotoxic injury, yet the mechanisms linking edema formation, glutamate dysregulation, and SD dynamics remain incompletely understood. Here, we investigated how inhibiting glial swelling and volume-regulated glutamate release, or blocking neuronal ionotropic glutamate receptors alters SD features under hypo-osmotic stress in vitro.Methods: Acute 350-µm-thick brain slices were prepared from male Wistar rats (n = 24). Edema was induced using hypoosmotic medium (130→60 mM NaCl), and SD was triggered by hypoxia. SD evolution and extracellular glutamate levels were monitored using local field potential recordings, intrinsic optical signal imaging, and enzyme-based glutamate biosensors. Astrocyte swelling was reduced by blocking AQP4+NKCC1 (TGN-020 + bumetanide) and VRAC channels (DCPIB), while neuronal NMDA and AMPA/kainate receptors were antagonized with MK-801 + CNQX.Results: Inhibition of AQP4, NKCC1, or VRAC channels restricted the cortical area invaded by SD, shortened SD duration, and reduced extracellular glutamate accumulation. In contrast, blockade of NMDA or AMPA/kainate receptors markedly decreased SD propagation and glutamate buildup. Both astrocytic and neuronal interventions disrupted typical SD initiation patterns, producing atypical, multifocal SD events. Discussion: These findings demonstrate that astrocyte volume regulation and neuronal ionotropic glutamate receptors jointly shape SD characteristics under osmotic stress, identifying astrocytic water/ion homeostasis and glutamatergic signaling as potential therapeutic targets to limit excitotoxic injury in acute cerebrovascular disease.”
#Andrew RD, Farkas E, Hartings JA, Brennan KC, Herreras O, Müller M, Kirov SA, Ayata C, Ollen-Bittle N, Reiffurth C, Revah O, Robertson RM, Dawson-Scully KD, Ullah G, Dreier JP. Questioning Glutamate Excitotoxicity in Acute Brain Damage: The Importance of Spreading Depolarization. Neurocrit Care. 2022
https://pmc.ncbi.nlm.nih.gov/articles/PMC9259542/
Quote: “Background
Within 2 min of severe ischemia, spreading depolarization (SD) propagates like a wave through compromised gray matter of the higher brain. More SDs arise over hours in adjacent tissue, expanding the neuronal damage. This period represents a therapeutic window to inhibit SD and so reduce impending tissue injury. Yet most neuroscientists assume that the course of early brain injury can be explained by glutamate excitotoxicity, the concept that immediate glutamate release promotes early and downstream brain injury. There are many problems with glutamate release being the unseen culprit, the most practical being that the concept has yielded zero therapeutics over the past 30 years. But the basic science is also flawed, arising from dubious foundational observations beginning in the 1950s
Methods
Literature pertaining to excitotoxicity and to SD over the past 60 years is critiqued.
Results
Excitotoxicity theory centers on the immediate and excessive release of glutamate with resulting neuronal hyperexcitation. This instigates poststroke cascades with subsequent secondary neuronal injury. By contrast, SD theory argues that although SD evokes some brief glutamate release, acute neuronal damage and the subsequent cascade of injury to neurons are elicited by the metabolic stress of SD, not by excessive glutamate release. The challenge we present here is to find new clinical targets based on more informed basic science. This is motivated by the continuing failure by neuroscientists and by industry to develop drugs that can reduce brain injury following ischemic stroke, traumatic brain injury, or sudden cardiac arrest. One important step is to recognize that SD plays a central role in promoting early neuronal damage. We argue that uncovering the molecular biology of SD initiation and propagation is essential because ischemic neurons are usually not acutely injured unless SD propagates through them. The role of glutamate excitotoxicity theory and how it has shaped SD research is then addressed, followed by a critique of its fading relevance to the study of brain injury.
Conclusions
Spreading depolarizations better account for the acute neuronal injury arising from brain ischemia than does the early and excessive release of glutamate.”
#Li YW, Liu Y, Luo SZ, Huang XJ, Shen Y, Wang WS, Lang ZC. The significance of calcium ions in cerebral ischemia-reperfusion injury: mechanisms and intervention strategies. Front Mol Biosci. 2025
https://pmc.ncbi.nlm.nih.gov/articles/PMC12104078/
Quote: “Calcium ions are central to understanding the complex mechanisms involved in CIRI (DI et al., 2024; Sharma et al., 2024a; Yaghoobi et al., 2024). As vital intracellular second messengers, they are critical in regulating the normal physiological functions of neurons (Bollimuntha et al., 2011; Ono et al., 2023; Jha et al., 2024). Including maintaining cell membrane potential and facilitating various biochemical reactions within cells. However, during CIRI, the balance of intracellular calcium ions is disrupted, leading to an excessive influx of calcium into the cells (Yue et al., 2017; Dai et al., 2024a; Yang et al., 2025). This calcium overload triggers a cascade of reactions that can damage and ultimately kill nerve cells (Payal et al., 2023; Sharma et al., 2024b; Singh et al., 2025). The consequences extend beyond direct cellular dysfunction; the activation of various enzymes, such as phospholipases, proteases, and nucleases, results in the destruction of cell membranes and organelles, further worsening brain tissue damage. Additionally, calcium overload is intricately linked to other injury mechanisms, including oxidative stress and inflammatory responses, creating a vicious cycle that exacerbates CIRI (Wang et al., 2017; Li et al., 2021a)”
#Farkas E, Rose CR. A dangerous liaison: Spreading depolarization and tissue acidification in cerebral ischemia. J Cereb Blood Flow Metab. 2025
https://pmc.ncbi.nlm.nih.gov/articles/PMC12000947/
Quote: “As mentioned above, marked changes in ion concentrations characterize SD. Extracellular K+ accumulates to 30–60 mM, with a concomitant decrease of neuronal K+ content from about 135 to around 100 mM. Furthermore, there are prominent ionic translocations of Na+ resulting in a decrease in [Na+]e from ∼150 to 60 mM and an increase in neuronal [Na+] from 10 to ∼40 mM. 42 Likewise, [Ca2+]e drops from 1.3 mM to 80 μM, while [Ca2+]i in neurons increases from about 60 nM to as high as 25 μM. SD thus represents the near-complete breakdown of transmembrane ion gradients synchronized in a critical volume of brain tissue (about 1 mm3), and propagates slowly as a wavefront over the gray matter in a self-igniting fashion. 40”
– A slow tsunami of death is spreading through your brain at the speed of a few millimeters per minute.
Here we describe the so-called “Spreading Depression/Depolarization” which is often observed after e.g. heart attacks/strokes, brain injuries etc.
#Andrew RD, Farkas E, Hartings JA, Brennan KC, Herreras O, Müller M, Kirov SA, Ayata C, Ollen-Bittle N, Reiffurth C, Revah O, Robertson RM, Dawson-Scully KD, Ullah G, Dreier JP. Questioning Glutamate Excitotoxicity in Acute Brain Damage: The Importance of Spreading Depolarization. Neurocrit Care. 2022
https://pmc.ncbi.nlm.nih.gov/articles/PMC9259542/
Quote: “SD is the principal mechanism of electrochemical membrane disruption and neuronal swelling [2–5] in gray matter of the higher brain. Severe ischemia depletes the adenosine triphosphate (ATP) pool, leading to Na+/K+ pump failure, which generates a front of cellular depolarization that propagates at 1–9 mm/min through the ischemic gray matter and even into healthy tissue [6–8]. The SD wave is a sudden loss of membrane potential to near-zero millivolts that occurs over seconds. SD can be evoked by various noxious electrical, chemical, thermal, or mechanical disturbances of gray matter that stress the Na+/K+ pump. Thus, SD is associated with a range of diseases and conditions, including migraine-associated aura, concussion, traumatic brain injury (TBI), subarachnoid hemorrhage, intracerebral hemorrhage, ischemic stroke, circulatory arrest, and brain death prior to circulatory collapse [1, 9–14]. SD can also invade gray matter that has not been metabolically compromised, inducing a loss of neuronal activity termed “spreading depression” [15].”
#Milakara D, Grozea C et al. Simulation of Spreading Depolarization Trajectories in Cerebral Cortex: Correlation of Velocity and Susceptibility in Patients with Aneurysmal Subarachnoid Hemorrhage. NeuroImage: Clinical (2017)
https://www.sciencedirect.com/science/article/pii/S2213158217302206
Quote: “In many cerebral grey matter structures including the neocortex, spreading depolarization (SD) is the principal mechanism of the near-complete breakdown of the transcellular ion gradients with abrupt water influx into neurons. Accordingly, SDs are abundantly recorded in patients with traumatic brain injury, spontaneous intracerebral hemorrhage, aneurysmal subarachnoid hemorrhage (aSAH) and malignant hemispheric stroke using subdural electrode strips. SD is observed as a large slow potential change, spreading in the cortex at velocities between 2 and 9 mm/min.”
#Ayata C, Lauritzen M. Spreading Depression, Spreading Depolarizations, and the Cerebral Vasculature. Physiol Rev. 2015
https://pmc.ncbi.nlm.nih.gov/articles/PMC4491545/
Quote: “As the name implies, the depolarization spreads at a rate of only a few millimeters in a minute, often centrifugally from the point of origin by way of grey matter contiguity, regardless of functional divisions or vascular territories (Figure 1D), although large cerebral arteries can sometimes act as barriers (137).”
– Are you experiencing anything in this phase? Maybe. There are reports of near death experiences and your brain is certainly flooded with chemicals that create a final surge of desperate activity.
Around the time of death from lack of oxygen (hypoxia), some human and animal studies show brief surges of activity just before or during the “electrical shutdown”.
#Mashour, GA., Lee U, Pal D, Li D. Consciousness and the Dying Brain. Anesthesiology (2024)
https://pmc.ncbi.nlm.nih.gov/articles/PMC11096058/
Quote: “The near-death experience has been reported since antiquity and is often characterized by the perception of light, interactions with other entities, and life recall. Near-death experiences can occur in a variety of situations, but they have been studied systematically after in-hospital cardiac arrest, with an incidence of 10 to 20%. Long attributed to metaphysical or supernatural causes, there have been recent advances in understanding the neurophysiologic basis of this unique category of conscious experience. This article reviews the epidemiology and neurobiology of near-death experiences, with a focus on clinical and laboratory evidence for a surge of neurophysiologic gamma oscillations and cortical connectivity after cardiac and respiratory arrest.”
#G. Xu, T. Mihaylova, D. Li, F. Tian, P.M. Farrehi, J.M. Parent, G.A. Mashour, M.M. Wang, & J. Borjigin, Surge of neurophysiological coupling and connectivity of gamma oscillations in the dying human brain, Proc. Natl. Acad. Sci. U.S.A. (2023).
https://www.pnas.org/doi/10.1073/pnas.2216268120
Quote: “Is it possible for the human brain to be activated by the dying process? We addressed this issue by analyzing the electroencephalograms (EEG) of four dying patients before and after the clinical withdrawal of their ventilatory support and found that the resultant global hypoxia markedly stimulated gamma activities in two of the patients. The surge of gamma connectivity was both local, within the temporo–parieto–occipital (TPO) junctions, and global between the TPO zones and the contralateral prefrontal areas. While the mechanisms and physiological significance of these findings remain to be fully explored, these data demonstrate that the dying brain can still be active. They also suggest the need to reevaluate role of the brain during cardiac arrest.”
#Chawla LS, Akst S, Junker C, Jacobs B, Seneff MG. Surges of electroencephalogram activity at the time of death: a case series. J Palliat Med. 2009
http://journals.sagepub.com/doi/abs/10.1089/jpm.2009.0159
Quote: “Level of consciousness at the end of life in critically ill patients is poorly characterized. We report a case series of seven patients who were neurologically intact before the decision to withdraw care due to extensive systemic critical illness. As part of our end-of-life care protocol, bispectral index (BIS) monitor (Aspect Medical Systems, Newton, MA) or SEDline™ (Hospira, Lake Forest, IL) monitoring devices are placed on each patient to ensure adequate comfort. Both monitoring systems use an integer-based system (BIS or PSI, respectively) to reflect the level of consciousness/effect of anesthesia. In each case, loss of blood pressure, as monitored by indwelling arterial line, was followed by a decline is BIS/PSI activity followed by a transient spike in BIS/PSI activity that approached levels normally associated with consciousness. This spike in electroencephalogram (EEG) activity had short duration and the activity then declined to a level of activity associated with burst suppression. In one case of a patient who had a SEDLine™ device, we were able to capture and analyze the raw EEG signal, and confirm that the EEG waveform was not artifact, and in fact a high frequency waveform was present during the spike activity. We speculate that this level of BIS/SEDline™ activity is related to the cellullar loss of membrane polarization due to hypoxemia. We further speculate that since this increase in electrical activity occurred when there was no discernable blood pressure, patients who suffer “near death” experiences may be recalling the aggregate memory of the synaptic activity associated with this terminal but potentially reversible hypoxemia.”
– But it is hard to tell, because in this moment your memories, dreams and identity are erased from the universe, as the structure that made you, you, is starting to turn into a gooey liquid mush.
#Sekhon, M.S., Ainslie, P.N. & Griesdale, D.E. Clinical pathophysiology of hypoxic ischemic brain injury after cardiac arrest: a “two-hit” model. Crit Care (2017)
https://link.springer.com/article/10.1186/s13054-017-1670-9
Quote: “Primary injury
During CA [cardiac arrest], cessation of CDO2 [cerebral oxygen delivery] occurs with resultant neuron ischemia and cell death within minutes [9] (Fig. 1). The cerebrum consumes 20% to 25% of cardiac output to maintain function [3]. The brain is devoid of nutrient stores, and consequently neuroglycopenia and metabolic crisis occur within minutes after CA [10], leading to cell death.
[...] As CDO2 decreases, adenosine triphosphate production halts, causing cessation of energy-dependent ion channel function [11]. Subsequent intracellular Na+ accumulation results in cytotoxic edema. Depletion of adenosine triphosphate leads to anaerobic metabolism, cerebral lactate accumulation, and intracellular acidosis [12]. Additionally, cellular ischemia causes intracellular Ca2+ influx through N-methyl-d-aspartate channels, which activates lytic enzymes [13] and mitochondrial dysfunction, thereby depleting adenosine triphosphate further [14]. Finally, excitatory neurotransmitter release activates lipases and proteases, which leads to apoptosis [15].
Clinically, loss of neurologic function is manifested by a decreased level of consciousness after global cerebral ischemia. Historically, Rossen et al. demonstrated that cessation of cerebral blood flow (CBF) by neck cuff insufflation to 600 mmHg in humans precipitated acute decreased level of consciousness within 10 seconds [16]. Decreased level of consciousness after CA occurs within 20 seconds after onset of ventricular fibrillation [17]. Loss of neurologic function has been demonstrated by isoelectric electroencephalography in observational studies [16]. Pana et al. identified human studies demonstrating isoelectric electroencephalography rhythms within 15 seconds and 30 seconds of asystole and ventricular fibrillation, respectively [16]. These findings are corroborated by animal studies establishing a similar timeline of 10 to 30 seconds from the onset of cerebral ischemia to isoelectric electroencephalography [18].”
#Levy AD, Harcke HT, Mallak CT. Postmortem imaging: MDCT features of postmortem change and decomposition. Am J Forensic Med Pathol. 2010
Quote: “In contrast, decomposition through autolysis, putrefaction, and insect and animal predation produce dramatic alterations in the appearance of the body on MDCT. Autolysis alters the attenuation of organs. The most dramatic autolytic changes on MDCT are seen in the brain where cerebral sulci and ventricles are effaced and gray-white matter differentiation is lost almost immediately after death.”
#Andrew RD, Farkas E, Hartings JA, Brennan KC, Herreras O, Müller M, Kirov SA, Ayata C, Ollen-Bittle N, Reiffurth C, Revah O, Robertson RM, Dawson-Scully KD, Ullah G, Dreier JP. Questioning Glutamate Excitotoxicity in Acute Brain Damage: The Importance of Spreading Depolarization. Neurocrit Care. 2022
https://pmc.ncbi.nlm.nih.gov/articles/PMC9259542/
Quote: “In the ischemic core, neurons will die under a maintained depolarization that typically lasts 20–30 min or more [16–19]. However, if the ischemic core is reperfused within ~ 15 min, all neurons will survive, even though persistently depolarized for about 15 min [18, 20]. In contrast, perfusion completely ceases after cardiac arrest, and so neurons start to die after about 5 min [21]. In milder in vivo models, there is no terminal SD (those with no recovery), but typically a cluster of recurrent moderately prolonged SDs occurs superimposed on a relatively shallow negative ultraslow potential. Yet cell death also develops. Clustered SD events pose particularly high metabolic challenge for recovery.”
– In less than 20 minutes your brain is irreversibly lost.
The “point of no return” – i.e., irreparable, “global” brain damage when deprived of oxygen – varies between people. No absolute “time cutoff” guarantees a good or bad outcome. Some people manage to survive (through e.g. resuscitation) after quite a long time (15-20 min) without oxygen, while other people’s brains are completely “gone” much earlier (less than 10 min).
It also strongly depends on environmental factors such as temperature: higher temperature means higher metabolism and thus faster brain death because brain cells are running out of energy more quickly. For some surgical procedures, the body is cooled to 18°C so that the brain survives up to 30-60 min without blood flow.
In general there is also a lack of data on the timeline for the scenario we are describing here (no CPR, no hospital) because by definition, those cases are not monitored clinically. There is therefore a bit of educated guessing involved here.
As a guideline for our “20 minutes” statement here, we used the following information:
When people are CPRed within 3-5 minutes, the survival rate is about 50% and quickly decreases with each additional minute that passes.
CPR up to 10 min after arrest can still increase the survival chances.
Beyond 12 min of cardiac arrest without resuscitation, survival becomes rare.
20 min of unresolved cardiac arrest is a common benchmark for stopping CPR.
An expert on clinical neurology and pathology provided us with an estimate of 20 min for irreversible brain death in the scenario we describe here (ambient temperature, no resuscitation).
#Cheema MA, Ullah W, Abdullah HMA, Haq S, Ahmad A, Balaratna A. Duration of in-hospital cardiopulmonary resuscitation and its effect on survival. Indian Heart J. 2019
https://pmc.ncbi.nlm.nih.gov/articles/PMC6890953/
Quote: “The American Heart Association (AHA) estimates that the survival rate for cardiac arrest is estimated to be around 50% in cases, where the CPR is administered within 3–5 min. However, this survival decreases by 7–10% with each minute that defibrillation is delayed.1”
#American Heart Association. Bystander CPR up to 10 minutes after cardiac arrest may protect brain function. 2024
Quote: “The sooner a lay rescuer (bystander) starts cardiopulmonary resuscitation (CPR) on a person having a cardiac arrest at home or in public, up to 10 minutes after the arrest, the better the chances of survival and brain protection, according to an analysis of nearly 200,000 out-of-hospital cardiac arrest cases in the U.S. from 2013 to 2022.”
#Adnet F, Triba MN, Borron SW, Lapostolle F, Hubert H, Gueugniaud PY, Escutnaire J, Guenin A, Hoogvorst A, Marbeuf-Gueye C, Reuter PG, Javaud N, Vicaut E, Chevret S. Cardiopulmonary resuscitation duration and survival in out-of-hospital cardiac arrest patients. Resuscitation. 2017
https://www.resuscitationjournal.com/article/S0300-9572(16)30579-2/abstract
Quote: “Methods
We analyzed 27,301 non-traumatic, witnessed OHCA patients in France included in the national registry from June 1, 2011 through December 1, 2015. We analyzed cardiac arrest intervals, designated as no-flow (NF; from collapse to start of CPR) and low-flow (LF; from start of CPR to cessation of resuscitation) in relation to 30-day survival without sequelae. We determined the influence of recognized prognostic factors (age, gender, initial rhythm, location of cardiac arrest) on this relation.
Results
For the entire cohort, the area delimited by a value of NF greater than 12min (95% confidence interval: 11–13min) and LF greater than 33min (95% confidence interval: 29–45min), yielded a probability of 30-day survival of less than 1%.”
#Youness H, Al Halabi T, Hussein H, Awab A, Jones K, Keddissi J. Review and Outcome of Prolonged Cardiopulmonary Resuscitation. Crit Care Res Pract. 2016
https://pmc.ncbi.nlm.nih.gov/articles/PMC4738728/
Quote: “In one large study, the overall median duration of resuscitation for in-hospital cardiac arrest was 17 minutes with an interquartile range of 10–26 min [3]. For out-of-hospital arrest, the National Association of Emergency Medical Services Physicians suggest that resuscitative efforts could be terminated in patients who do not respond to at least 20 minutes of advanced life support care [4].”
From Prof. Ulrich Dirnagl (Charité – Universitätsmedizin Berlin) we also received the following insight: "Cardiac arrest of 10 minutes can be survived after successful resuscitation, if a person is lucky even without major deficits. It very much depends on environmental factors. In hypothermic cardiac surgery, cardiac arrest is often induced for 30 to 60 min (at 18 oC). Without cooling, I'd say 20 minutes is a good guess for irreversibility."
#Andrew RD, Farkas E, Hartings JA, Brennan KC, Herreras O, Müller M, Kirov SA, Ayata C, Ollen-Bittle N, Reiffurth C, Revah O, Robertson RM, Dawson-Scully KD, Ullah G, Dreier JP. Questioning Glutamate Excitotoxicity in Acute Brain Damage: The Importance of Spreading Depolarization. Neurocrit Care. 2022
https://pmc.ncbi.nlm.nih.gov/articles/PMC9259542/
Quote: “In the ischemic core, neurons will die under a maintained depolarization that typically lasts 20–30 min or more [16–19]. However, if the ischemic core is reperfused within ~ 15 min, all neurons will survive, even though persistently depolarized for about 15 min [18, 20]. In contrast, perfusion completely ceases after cardiac arrest, and so neurons start to die after about 5 min [21]. In milder in vivo models, there is no terminal SD (those with no recovery), but typically a cluster of recurrent moderately prolonged SDs occurs superimposed on a relatively shallow negative ultraslow potential. Yet cell death also develops. Clustered SD events pose particularly high metabolic challenge for recovery.”
– Many societies and legal systems treat this as your death.
Here we refer to legal death as a consequence of brain death. Various definitions and medical criteria exist for this, and they can vary by country. The criteria and definitions have also changed over time as medicine progressed, and are subject of scientific and legal debate to this day.
USA:
#Cleveland Clinic. Brain Death. Retrieved May 2026
https://my.clevelandclinic.org/health/diseases/brain-death
Quote: ““Brain death” is the medical and legal term for death that happens when your brain stops working. In brain death, injury or illness does severe, permanent damage to your entire brain and brainstem. Your brainstem manages your breathing and heart rate. Your brain manages senses like sight, sound and touch, and abilities like motor movement.
Because people’s brains drive these essential functions, someone is legally dead when they’re diagnosed with brain death. Healthcare providers follow established medical criteria (guidelines) to determine if someone is brain dead. For example, they rule out all other possible causes before they do specific tests that diagnose brain death.
[...] What is the main cause of brain death?
Many things may cause severe, permanent brain damage that leads to brain death. For example, your brain needs blood and oxygen to function, so any serious injury or illness that keeps blood and oxygen from your brain may cause brain death. Likewise, any injury or illness that damages blood vessels in your brain and causes bleeding may lead to it. Potential causes include:
Traumatic brain injury.
Intracerebral hemorrhage (brain bleed).
Subarachnoid hemorrhage.
Ischemic stroke.
Heart attack.
Hypoxic ischemic brain injury (HIBI), when your brain doesn’t get oxygen.
Intracranial infections like meningitis or encephalitis.
[...] What are the medical criteria for brain death?
The term “medical criteria” refers to the steps healthcare providers must take in diagnosing brain death. In the U.S., three medical societies collaborate on criteria. Before providers can do tests to diagnose brain death, they:
Identify and treat any underlying condition that’s causing severe brain damage.
Rule out potential issues and conditions that could be why someone has severe brain damage.
Rule out conditions or issues that could cause symptoms that mimic brain death.
What tests are done to determine brain death?
Healthcare providers with special training in brain death do several tests. They may do tests more than once to confirm their initial diagnosis. If your provider suspects you have brain death, they’ll tell your family about the tests and what the tests might show. Tests include a physical examination, imaging tests like a brain MRI, an extensive neurological examination and an apnea test.
Neurological examination
In brain death, you don’t react to noise, lights or touch as you would before your brain injury. You may move, but your movement is involuntary, meaning you didn’t move on purpose. Providers doing a neurological examination to diagnose brain death will:
Check your gag or choking reflex by touching the back of your throat.
Check your eye reflexes by touching an eye with a cotton swab to see if you flinch, blink, close your eye or move your head.
Check your pupils’ response to light.
Apnea test
If you have a catastrophic brain injury, you can’t breathe on your own and rely on mechanical ventilation (ventilators). In an apnea test, providers briefly stop ventilator support to see if you take a breath on your own.”
UK:
#National Health Service – Brain death. Retrieved May 2026
https://www.nhs.uk/conditions/brain-death/
Quote: “Brain death (also known as brain stem death) is when a person on an artificial life support machine no longer has any brain functions. This means they will not regain consciousness or be able to breathe without support.
A person who is brain dead is legally confirmed as dead. They have no chance of recovery because their body is unable to survive without artificial life support.
Brain death is legal death
If someone is brain dead, the damage is irreversible and, according to UK law, the person has died. It can be confusing to be told someone has brain death, because their life support machine will keep their heart beating and their chest will still rise and fall with every breath from the ventilator. But they will not ever regain consciousness or start breathing on their own again. They have already died.
The brain stem
The brain stem is the lower part of the brain that's connected to the spinal cord (part of the central nervous system in the spinal column). The brain stem is responsible for regulating most of the body's automatic functions that are essential for life.
These include:
breathing
heartbeat
blood pressure
swallowing
The brain stem also relays information to and from the brain to the rest of the body, so it plays an important role in the brain's core functions, such as consciousness, awareness and movement. After brain death, it is not possible for someone to remain conscious.
Causes of brain death
Brain death can happen when the blood or oxygen supply to the brain is stopped.
This can be caused by:
cardiac arrest – when the heart stops beating and the brain is starved of oxygen
a heart attack – when the blood supply to the heart is suddenly blocked
a stroke – when the blood supply to the brain is blocked or interrupted
a blood clot – a blockage in a blood vessel that disturbs or blocks the flow of blood around your body
Brain death can also be caused by:
a severe head injury
a brain haemorrhage
infections, such as encephalitis
a brain tumour”
– At this point you can still save a few lives if you are an organ donor – but the rest of your body is on a tight timer.
Whether organ donation is possible depends on many things – among them the “survival” times of organs after cessation of blood flow, guided by acceptable “warm ischemia times” (WITs): the period when organs remain at normal (or near-normal) body temperature without oxygenated blood flow, i.e. before cooling or preservation. Acceptable WIT vary by country and transplant system, and doctors are often encouraged to assess donor organ suitability on a case by case basis, so these limits are not absolute rules.
This is also an active area of research, with ongoing efforts focused on extending acceptable WITs without compromising transplant outcomes.
When organs are properly preserved (e.g. cooled or maintained ex vivo), they can remain viable for far longer than we allude to in this video. Our timeline refers specifically to unmitigated or “natural” deterioration without preservation efforts.
#Australian and New Zealand Intensive Care Society. Statement on death and organ donation. 2021
https://anzics.org/wp-content/uploads/2022/04/ANZICS-Statement-on-Death-and-Organ-Donation.pdf
Quote: “Organs have different susceptibility to warm ischaemia with the liver and heart being particularly vulnerable. A guide to current acceptable ischaemic times in Australia and New Zealand is as follows, although individual donor and recipient factors may influence this on a case-by-case basis.
Australia:
liver, pancreas: <30 minutes from withdrawal of cardiorespiratory support to cold perfusion
heart: <30 minutes from when systolic blood pressure falls below 90 mmHg following withdrawal of cardiorespiratory support to cold perfusion
kidneys: <60 minutes from when systolic blood pressure falls below 50 mmHg post withdrawal of cardiorespiratory support to cold perfusion [...]
New Zealand:
liver: ≤30 minutes from withdrawal of cardiorespiratory support to cold perfusion
kidneys, Lungs: ≤90 minutes from withdrawal of cardiorespiratory support to death”
#Gerosa G, Luciani GB, Pradegan N, Tarzia V, Lena T, Zanatta P, Pittarello D, Onorati F, Galeone A, Gottin L, Boffini M, Zanierato M, Marro M, Martin Suarez S, Botta L, Lilla Della Monica P, Feccia M, Olivieri GM, Terzi A, Oliveti A, Feltrin G, Cardillo M, Russo CF, Pacini D, Rinaldi M. Against Odds of Prolonged Warm Ischemia: Early Experience With DCD Heart Transplantation After 20-Minute No-Touch Period. Circulation. 2024
https://www.ahajournals.org/doi/10.1161/CIRCULATIONAHA.124.071239
Quote: “The literature focuses on HT after <30 minutes functional warm ischemia time (primarily because of <10 minutes no-touch period time),4 but our early experience shows that 20-minute no-touch period does not preclude the possibility of early successful HT. In our small cohort, we observed normal heart recovery in terms of left ventricle function, with 30-day mortality rate similar to current DCD experience.4”
#British Transplantation Society. Guidelines relating to solid organ transplants from non-heart beating donors. 2004
https://bts.org.uk/wp-content/uploads/2016/09/NonHeart.pdf
Quote: “Warm ischaemic time less than or equal to 20 minutes for the liver and less than or equal to 40 minutes for the kidneys.”
#Paterno F, Guarrera JV, Wima K, Diwan T, Cuffy MC, Anwar N, Woodle ES, Shah S. Clinical Implications of Donor Warm and Cold Ischemia Time in Donor After Circulatory Death Liver Transplantation. Liver Transpl. 2019
Quote: “During the study period, 2107 patients underwent liver transplant with DCD allografts. In most patients, DWIT and DAT were <30 minutes. DWIT was <30 minutes in 1804 donors, between 30 and 40 minutes in 248, and >40 minutes in 37. There was no difference in graft survival, duration of posttransplant hospital length of stay, and readmission rate between DCD liver transplants from donors with DWIT <30 minutes and DWIT between 30 and 40 minutes.”
– The blackout spreads to your heavy industry: Organs that perform continuous, demanding work, like your liver, kidneys and your stopped heart go into survival mode.
When the heart stops, organs such as the liver and kidneys can survive for a while (30-60 min) even in the absence of brain activity. It is why organ transplants are possible. The crucial time span in which they are still considered suitable for donation is called “(Warm) Ischemia Time”.
#Australian and New Zealand Intensive Care Society. Statement on death and organ donation. 2021
https://anzics.org/wp-content/uploads/2022/04/ANZICS-Statement-on-Death-and-Organ-Donation.pdf
Quote: “Organs have different susceptibility to warm ischaemia with the liver and heart being particularly vulnerable. A guide to current acceptable ischaemic times in Australia and New Zealand is as follows, although individual donor and recipient factors may influence this on a case-by-case basis.
Australia:
liver, pancreas: <30 minutes from withdrawal of cardiorespiratory support to cold perfusion
heart: <30 minutes from when systolic blood pressure falls below 90 mmHg following withdrawal of cardiorespiratory support to cold perfusion
kidneys: <60 minutes from when systolic blood pressure falls below 50 mmHg post withdrawal of cardiorespiratory support to cold perfusion [...]
New Zealand:
liver: ≤30 minutes from withdrawal of cardiorespiratory support to cold perfusion
kidneys, Lungs: ≤90 minutes from withdrawal of cardiorespiratory support to death”
#British Transplantation Society. Guidelines relating to solid organ transplants from non-heart beating donors. 2004
https://bts.org.uk/wp-content/uploads/2016/09/NonHeart.pdf
Quote: “Warm ischaemic time less than or equal to 20 minutes for the liver and less than or equal to 40 minutes for the kidneys.”
#Paterno F, Guarrera JV, Wima K, Diwan T, Cuffy MC, Anwar N, Woodle ES, Shah S. Clinical Implications of Donor Warm and Cold Ischemia Time in Donor After Circulatory Death Liver Transplantation. Liver Transpl. 2019
Quote: “During the study period, 2107 patients underwent liver transplant with DCD allografts. In most patients, DWIT and DAT were <30 minutes. DWIT was <30 minutes in 1804 donors, between 30 and 40 minutes in 248, and >40 minutes in 37. There was no difference in graft survival, duration of posttransplant hospital length of stay, and readmission rate between DCD liver transplants from donors with DWIT <30 minutes and DWIT between 30 and 40 minutes.”
#Gerosa G, Luciani GB, Pradegan N, Tarzia V, Lena T, Zanatta P, Pittarello D, Onorati F, Galeone A, Gottin L, Boffini M, Zanierato M, Marro M, Martin Suarez S, Botta L, Lilla Della Monica P, Feccia M, Olivieri GM, Terzi A, Oliveti A, Feltrin G, Cardillo M, Russo CF, Pacini D, Rinaldi M. Against Odds of Prolonged Warm Ischemia: Early Experience With DCD Heart Transplantation After 20-Minute No-Touch Period. Circulation. 2024
https://www.ahajournals.org/doi/10.1161/CIRCULATIONAHA.124.071239
Quote: “The literature focuses on HT after <30 minutes functional warm ischemia time (primarily because of <10 minutes no-touch period time),4 but our early experience shows that 20-minute no-touch period does not preclude the possibility of early successful HT. In our small cohort, we observed normal heart recovery in terms of left ventricle function, with 30-day mortality rate similar to current DCD experience.4”
– They have one key advantage over the brain: large reserves of sugar and an emergency generator. The chemistry is complicated but in a nutshell: they can get energy from sugar without oxygen.
The liver stores a lot of sugar in the form of glycogen molecules, and the heart and kidney can also store some glycogen (of those three, the kidney stores the least of it).
Cells in all three organs have access to the “emergency hack” which is a process called “anaerobic glycolysis”. It can provide energy to cells without oxygen, as long as there is fuel (e.g. glucose or glycogen) around. Different types of cells are better or worse at anaerobic glycolysis, depending e.g. on how much glucose/glycogen they have stored inside them.
Much of what is known about anaerobic glycolysis postmortem comes from non-human animal studies, since it is quite hard to study in humans actively suffering from hypoxia (for obvious reasons). But the biology is broadly the same and one can plausibly extrapolate from there.
Liver:
#Soon GST, Torbenson M. The Liver and Glycogen: In Sickness and in Health. Int J Mol Sci. 2023
https://pmc.ncbi.nlm.nih.gov/articles/PMC10094386/
Quote: “The liver is a major store of glycogen. Glycogen is a branched polymer of glucose that is synthesized through the actions of glycogenin, glycogen synthase, and glycogen branching enzyme [7]. Glycogenin initiates the formation of a primary glucose chain and subsequently interacts with glycogen synthase to lengthen the glycogen-initiating particle. α-1,6-linkages are then added to the glycogen molecule by a glycogen-branching enzyme to create the final, spherical glycogen particle.
[...] The liver contains two types of glycogen: small β particles and larger α particles; the latter is a composite aggregate of β-particles [9]. α-particles release glucose more slowly than β-particles in the presence of degradative enzymes [10], thereby helping to maintain blood glucose levels during overnight fasting in diurnal mammals. Most glycogen is cytosolic, with up to 10% of glycogen in hepatocytes present within lysosomes [7].
In a normal state, all hepatocytes contain glycogen. The amount of glycogen is largely homogeneously distributed through out the liver lobule, although there can be zonal variations depending on the fasting or post-prandial state, corresponding to zonal variations in metabolic enzymatic activity [11].”
#Baze MM, Schlauch K, Hayes JP. Gene expression of the liver in response to chronic hypoxia. Physiol Genomics. 2010
https://pmc.ncbi.nlm.nih.gov/articles/PMC2869108/
Quote: “For example, acute hypoxia stimulates cells to switch from oxidative phosphorylation to anaerobic glycolysis, while perhaps decreasing fatty acid utilization. Increased gluconeogenesis performed by the liver can supply these hypoxic tissues with the glucose that they require (16) while increasing lipid storage of circulating fatty acids (13, 76). [...] Finally, the liver is one of the few tissues that expresses all three HIF isoforms (HIF-1α, HIF-2α, and HIF-3α), which suggests that it is important in responding to hypoxic conditions (76). Because the liver is a key mediator of metabolic process and because it plays an important role in acclimatization to hypoxic, we focused our study on the liver (52).”
#Chan TS, Cassim S, Raymond VA, Gottschalk S, Merlen G, Zwingmann C, Lapierre P, Darby P, Mazer CD, Bilodeau M. Upregulation of Krebs cycle and anaerobic glycolysis activity early after onset of liver ischemia. PLoS One. 2018
https://pmc.ncbi.nlm.nih.gov/articles/PMC6002017/
Quote: “The liver is a highly vascularized organ receiving a dual input of oxygenated blood from the hepatic artery and portal vein. The impact of decreased blood flow on glucose metabolism and how hepatocytes could adapt to this restrictive environment are still unclear. Using the left portal vein ligation (LPVL) rat model, we found that cellular injury was delayed after the onset of liver ischemia. We hypothesized that a metabolic adaptation by hepatocytes to maintain energy homeostasis could account for this lag phase. Liver glucose metabolism was characterized by 13C- and 1H-NMR spectroscopy and analysis of high-energy metabolites. ALT levels and caspase 3 activity in LPVL animals remained normal during the first 12 h following surgery (P<0.05). Ischemia rapidly led to decreased intrahepatic tissue oxygen tension and blood flow (P<0.05) and increased expression of Hypoxia-inducible factor 1-alpha. Intrahepatic glucose uptake, ATP/ADP ratio and energy charge level remained stable for up to 12 h after ligation. Entry of glucose in the Krebs cycle was impaired with lowered incorporation of 13C from [U-13C]glucose into glutamate and succinate from 0.25 to 12 h after LPVL. However, total hepatic succinate and glutamate increased 6 and 12 h after ischemia (P<0.05). Glycolysis was initially reduced (P<0.05) but reached maximum 13C-lactate (P<0.001) and 13C-alanine (P<0.01) enrichments 12 h after LPVL. In conclusion, early liver homeostasis stems from an inherent ability of ischemic hepatocytes to metabolically adapt through increased Krebs cycle and glycolysis activity to preserve bioenergetics and cell viability. This metabolic plasticity of hepatocytes could be harnessed to develop novel metabolic strategies to prevent ischemic liver damage.”
Heart:
#Xiang KF, Wan JJ, Wang PY, Liu X. Role of glycogen in cardiac metabolic stress. Metabolism. 2025
https://www.sciencedirect.com/science/article/abs/pii/S0026049524002877
Quote: “Cardiac glycogen serves as a pivotal reserve for myocardial energy, which is classically described as an energy source and contributes to glucose homeostasis during hypoxia or ischemia.
[...] In mammals, skeletal muscle and the liver serve as the principal glycogen repositories. Other organs also produce this polysaccharide, but their functions have been ignored due to their lower content. Research advances have illuminated the critical role of glycogen in pathophysiological activities across a spectrum of vital tissues, such as adipose [3], brain [4], tumor [5], and heart [6].”
#Li H, Xiao F, Zhou C, Zhu T, Wang S. Metabolic Adaptations and Therapies in Cardiac Hypoxia: Mechanisms and Clinical Implications/ Potential Strategies. JACC Basic Transl Sci. 2025
https://www.sciencedirect.com/science/article/pii/S2452302X24004583
Quote: “In the early phase of hypoxia, metabolic changes occur independently of HIF activation. Cells rapidly switch from oxidative phosphorylation to anaerobic glycolysis, producing ATP to sustain energy demands despite the lack of oxygen. During this stage, enzymes such as AMPK (AMP-activated protein kinase) are activated to promote glucose uptake and inhibit ATP-consuming processes. This quick response allows the cell to adapt to sudden oxygen deprivation before transcriptional changes through HIF-1α become active (Central Illustration).”
Kidneys:
#Gronda E, Jessup M, Iacoviello M, Palazzuoli A, Napoli C. Glucose Metabolism in the Kidney: Neurohormonal Activation and Heart Failure Development. J Am Heart Assoc. 2020
https://www.ahajournals.org/doi/10.1161/JAHA.120.018889
Quote: “The kidney together with the liver is 1 of 2 body organs provided with gluconeogenesis capability and roughly contributes to 20% glycogen production in normal physiology. In the kidney, gluconeogenesis takes place in the cortical cells while the medullary cells metabolize glucose.”
#Schaub JA, Venkatachalam MA, Weinberg JM. Proximal Tubular Oxidative Metabolism in Acute Kidney Injury and the Transition to CKD. Kidney360. 2020
https://pmc.ncbi.nlm.nih.gov/articles/PMC8740982/
Quote: “In summary, during the initial oxygen deprivation insult, very small amounts of ATP are required to maintain cell viability and enable recovery of mitochondrial oxidative metabolism via effects to limit fatty acid uncoupling, increase NAD, and likely preserve respiratory complex organization via regulation of mitochondrial volume and cristae structure. These levels of ATP cannot be provided by glycolysis in proximal tubules, but can be produced by anaerobic mitochondrial metabolism.”
– Though way less efficient, it buys them up to an hour of precious time.
The “one hour” is based on minimal “survival” times for organs after the cessation of blood flow; which in turn are based on guidelines for acceptable “Warm ischemia times” (= cessation of blood flow at or near body temperature) for organ transplantation. What is deemed “acceptable” depends on the country/region, and doctors are often encouraged to make case-by-case calls regarding the suitability of a donor organ – i.e., these are not hard and fast rules, more akin to recommendations. Suitable times for transplanting an organ are also an active area of research, so they might change in the future as medical technology progresses.
The “one hour” also assumes the organ remains in the (naturally-decaying) body, as is the case for our story scenario. But when stored appropriately outside the body, organs can remain viable much longer (typically for several hours, up to 24 h).
#Australian and New Zealand Intensive Care Society. Statement on death and organ donation. 2021
https://anzics.org/wp-content/uploads/2022/04/ANZICS-Statement-on-Death-and-Organ-Donation.pdf
Quote: “Organs have different susceptibility to warm ischaemia with the liver and heart being particularly vulnerable. A guide to current acceptable ischaemic times in Australia and New Zealand is as follows, although individual donor and recipient factors may influence this on a case-by-case basis.
Australia:
liver, pancreas: <30 minutes from withdrawal of cardiorespiratory support to cold perfusion
heart: <30 minutes from when systolic blood pressure falls below 90 mmHg following withdrawal of cardiorespiratory support to cold perfusion
kidneys: <60 minutes from when systolic blood pressure falls below 50 mmHg post withdrawal of cardiorespiratory support to cold perfusion [...]
New Zealand:
liver: ≤30 minutes from withdrawal of cardiorespiratory support to cold perfusion
kidneys, Lungs: ≤90 minutes from withdrawal of cardiorespiratory support to death”
#British Transplantation Society. Guidelines relating to solid organ transplants from non-heart beating donors. 2004
https://bts.org.uk/wp-content/uploads/2016/09/NonHeart.pdf
Quote: “Warm ischaemic time less than or equal to 20 minutes for the liver and less than or equal to 40 minutes for the kidneys.”
#Paterno F, Guarrera JV, Wima K, Diwan T, Cuffy MC, Anwar N, Woodle ES, Shah S. Clinical Implications of Donor Warm and Cold Ischemia Time in Donor After Circulatory Death Liver Transplantation. Liver Transpl. 2019
Quote: “During the study period, 2107 patients underwent liver transplant with DCD allografts. In most patients, DWIT and DAT were <30 minutes. DWIT was <30 minutes in 1804 donors, between 30 and 40 minutes in 248, and >40 minutes in 37. There was no difference in graft survival, duration of posttransplant hospital length of stay, and readmission rate between DCD liver transplants from donors with DWIT <30 minutes and DWIT between 30 and 40 minutes.”
#Gerosa G, Luciani GB, Pradegan N, Tarzia V, Lena T, Zanatta P, Pittarello D, Onorati F, Galeone A, Gottin L, Boffini M, Zanierato M, Marro M, Martin Suarez S, Botta L, Lilla Della Monica P, Feccia M, Olivieri GM, Terzi A, Oliveti A, Feltrin G, Cardillo M, Russo CF, Pacini D, Rinaldi M. Against Odds of Prolonged Warm Ischemia: Early Experience With DCD Heart Transplantation After 20-Minute No-Touch Period. Circulation. 2024
https://www.ahajournals.org/doi/10.1161/CIRCULATIONAHA.124.071239
Quote: “The literature focuses on HT after <30 minutes functional warm ischemia time (primarily because of <10 minutes no-touch period time),4 but our early experience shows that 20-minute no-touch period does not preclude the possibility of early successful HT. In our small cohort, we observed normal heart recovery in terms of left ventricle function, with 30-day mortality rate similar to current DCD experience.4”
– As your organs’ cells switch from regular breathing to the emergency generator, some of their genes ramp up their activity, activating machinery to respond to stress and repair damage to survive as long as they can – but for many of your cells the stress becomes too great. They use the emergency system to destroy themselves in a quiet, orderly way.
Controlled cell death (“apoptosis”) is triggered postmortem in many cells across the body through cell stress due to various consequences of oxygen deprivation (oxidative stress/reactive oxygen species, ATP depletion, DNA damage etc.). It is quite hard to quantify how much apoptosis is happening as opposed to "uncontrolled" cell death, because cells die from many causes postmortem (necrosis, autolysis, later also putrefaction, etc.). But we do know that apoptosis genes show high activity, i.e. many of them are upregulated shortly after death.
Much of what is known about apoptosis comes from (non-human) animal studies, but the basic biological processes are extremely similar if not identical in humans.
Apoptosis in humans:
#Javan GT, Singh K, Finley SJ, Green RL and Sen CK (2024) Complexity of human death: its physiological, transcriptomic, and microbiological implications. Front. Microbiol.
https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2023.1345633/full
Quote: “Reports have associated the initiation of apoptosis in human cells at the phase of death as cells struggle to persist. Genetic studies of key regulators of apoptosis using liver tissues from autopsied samples, showed substantial down-regulation of the expression of anti-apoptotic functional gene groups and an up-regulation of pro-apoptosis genes for up to 4 days (Javan et al., 2015). Specifically, RNA expression levels of BNIP3L (anti-apoptotic), CASP1 (anti-apoptotic), CRADD (anti-apoptotic), DFFA (pro-apoptotic), and DIABLO (pro-apoptotic) were reduced. AIFM1 (pro-apoptotic), CASP3 (pro-apoptotic), CASP7 (pro-apoptotic), FADD (anti-apoptotic), and XIAP (anti-apoptotic) gene expressions increased. We hypothesize that these divergent conclusions are potentially due to mechanisms to achieve homeostatic equilibrium between the pro- and anti-apoptotic signals that are activated or decreasing in activity in decaying tissues to maintain cell survival. The expression of the anti-apoptotic gene XIAP, the most potent natural inhibitor of apoptosis, was greater than 28-fold after organismal death. In a related postmortem gene expression analysis of Italian cadaver prostate tissue, there was a marked up-regulation of mRNA transcripts that were still detectable up to 5 days after death. This study also demonstrated increased expression of XIAP and other pro-survival genes such as BAG1 and BCL2 (Tolbert et al., 2018).”
Apoptosis in slaughtered animals:
#Zhao Y, Xiang C, Roy BC, Bruce HL, Blecker C, Zhang Y, Liu C, Zhang D, Chen L, Huang C. Apoptosis and its role in postmortem meat tenderness: A comprehensive review. Meat Sci. 2025
https://www.sciencedirect.com/science/article/abs/pii/S0309174024002298
Quote: “After animals are slaughtered and exsanguinated, there is a significant accumulation of reactive oxygen species (ROS), and a dramatic depletion of adenosine triphosphate (ATP) in muscle, leading to inevitable cell death. Caspases are activated in postmortem muscle cells, which disrupt the cell structure and improve meat tenderness through protein hydrolysis. In this review, we systematically summarized the three primary types of cell death studied in postmortem muscle: apoptosis, autophagy and necrosis. Furthermore, we emphasized the molecular mechanisms of apoptosis and its corresponding apoptotic pathways (mitochondrial apoptosis, death receptors, and endoplasmic reticulum stress) that affect meat tenderness during muscle conversion to meat. Additionally, factors affecting apoptosis were comprehensively discussed, such as ROS, heat shock proteins, calcium (Ca2+)/calpains, and Bcl-2 family proteins. Finally, this comprehensive review of existing research reveals that apoptosis is mainly mediated by the mitochondrial pathway. This ultimately leads to myofibrillar proteins degradation through caspase activation, improving meat tenderness. This review summarizes the research progress on postmortem muscle apoptosis and its molecular mechanisms in meat tenderization.”
#Zou B, Jia F et al. Changes of postmortem apoptotic factors, genes and proteins and their potential associations with beef tenderization. Food Science of Animal Products. 2023
https://www.sciopen.com/article/10.26599/FSAP.2023.9240040
Quote: “Apoptosis in postmortem muscle is a potential factor affecting meat quality. This study aimed to investigate the changes in apoptotic genes and proteins, reactive oxygen species (ROS), caspase-3 activity and their underlying relationship with meat tenderization. As postmortem time extended, there was a significant increase in myofibril fragmentation index (MFI) and destruction of muscle fibers. Oxidative stress deepened alongside the onset of apoptosis. Mitochondrial membrane potential (MMP) decreased, and caspase-3 activity increased during the first 24 h postmortem. Forty apoptotic genes displayed significant differences, involving DNA damage, autophagy, the death receptor pathway, the mitochondrial pathway, the Bcl-2 family, and the caspases family. The expression of most apoptotic genes was abundant in the early postmortem stage, enhancing the potential for early apoptosis.”
#Martínez PN, Menéndez ST, Villaronga MLÁ, Ubelaker DH, García-Pedrero JM, C Zapico S. "The big sleep: Elucidating the sequence of events in the first hours of death to determine the postmortem interval". Sci Justice. 2019
https://www.sciencedirect.com/science/article/abs/pii/S1355030618303575?via%3Dihub
Quote: “Recent developments on postmortem interval estimation (PMI) take an advantage of the autolysis process, pointing out to the analysis of the expression of apoptosis and autophagy genes towards this purpose. Oxidative stress plays a role in this signaling as a regulatory mechanism and/or as a consequence of cell death. Additionally, melatonin has been implicated on apoptosis and autophagy signaling, making melatonin a suitable target for PMI determination. The aim of this study was to investigate the early PMI through the analysis of the expression of autophagy genes as well as oxidative stress and melatonin receptor. Our results demonstrated a rapidly increased on the expression of autophagy genes according to the expected sequence of events, then a marked decrease in this expression, matched with the switch to the apoptosis signaling. These results revealed potential candidates to analyze the PMI in the first hours of death, helping to estimate the time-since-death.”
Apoptosis does not alert the immune system to danger, i.e. it does not cause inflammation. Just some immune cells (phagocytes) are recruited to clean up the dead cells.
#Campisi L, Cummings RJ, Blander JM. Death-defining immune responses after apoptosis. Am J Transplant. 2014
https://pmc.ncbi.nlm.nih.gov/articles/PMC4115279/
Quote: “The primary purpose for apoptosis is to dispose of unwanted cells in a controlled manner (8). In doing so, dying cells undergo a well-organized and coordinated internal dismantling in an effort to minimize damage to neighboring cells and prevent tissue stress (2). One way this can be achieved is through the release of immunosuppressive cytokines including IL-10 and TGF-β from both apoptotic cells and phagocytic cells responding to apoptosis (2). Phagocytic cells sense and clear apoptotic cell corpses via a sequence of “find me” and “eat me” signals expressed by dying cells (10). Examples of “find me” signals and the corresponding receptors on phagocytic cells directing chemotaxis include the G protein coupled receptor G2A, as well as sphingosine-1-phosphate (S1P) and the S1P-receptor 1 (10). “Eat me” signals on the apoptotic cell surface, such as phosphatidylserine (PtdSer), can then “directly” or “indirectly” trigger phagocytosis. For “direct” triggering, the T cell immunoglobulin and mucin domain (TIM) family of phagocytic receptors are required whereas “indirect” triggering is achieved via αvβ3/5 integrins that bind the MΦ secreted product known as milk fat globule-EGF factor 8 (MFG-E8) in complex with PtdSer to enhance corpse clearance (10). These “find me” and “eat me” signals as well as the corresponding receptors have recently been reviewed by Hochreiter-Hufford and Ravichandran (10).
Not only do the release of the aforementioned cytokines and detection of “find me”/“eat me” signals condition the surrounding microenvironment, they also direct differentiation of regulatory T cells (Tregs), which supplement the suppressive nature of the apoptotic milieu (2). Moreover, the membrane of a dying cell is preserved during apoptosis concealing many potentially immunogenic DAMPs which if released could alert surrounding cells, including phagocytic cells, by triggering both surface and cytosolic PRR.”
– For the cells still trying to hold on, the emergency energy comes at a huge cost. Without oxygen, sugar is broken down incompletely and turns into lactic acid that degenerates their insides.
After death, cells lose oxygen and shift from aerobic to anaerobic glycolysis, converting glucose to lactate. This causes lactic acid (or lactate, in the body’s neutral pH) to accumulate in the body during the early postmortem period.
#Donaldson AE, Lamont IL. Biochemistry changes that occur after death: potential markers for determining post-mortem interval. PLoS One. 2013
https://pmc.ncbi.nlm.nih.gov/articles/PMC3836773/
Quote: “Antemortem blood pH is regulated to stay within the narrow range of 7.35 to 7.45. If the blood pH is alkaline (greater than 7.45) or acidic (less than 7) this can lead to death [3] so blood pH is one of the most regulated systems in the body. Blood pH is regulated by acid-base buffers such as carbonic acid and biocarbonate ion, which exert their influence principally through the respiratory system and the kidneys in order to control the acid-base balance [3]. In death, the body buffering system is not maintained and blood pH changes can occur [4].
An early study reported that after death cardiac blood taken directly from 11 individual human remains showed a pH change from 7.0 to 5.5 by 20 hours post-mortem [5]. In the same study, blood collected from rat corpses showed a pH decrease from 7.35 at antemortem to 5.5 by 96 hours post-mortem.
A lower blood pH must reflect the accumulation of acidic metabolites. Lactic acid is produced by lactate dehydrogenase from pyruvate via anaerobic glycolysis in skeletal muscle, liver and red blood cells when insufficient oxygen is available for pyruvate to enter the citric acid cycle. This process occurs naturally in muscle tissue during exercise and in normal metabolism inside red blood cells. The normal serum lactate concentration is 0.5-2.2 mmol.L-1. Circulating lactate is normally oxidised to pyruvate through the actions of lactate dehydrogenase (LDH) after being taken up by monocarboxylate transport proteins (MCTs) that are differentially expressed in actively respiring cells and tissues [6]. In the only recent study of lactate concentration in blood post-mortem, lactate in human heart blood increased 20-fold by one hour after death and 50-70 fold by 24 hours [2].
[...] The most immediate biochemical change that occurred post-mortem is a fall in the concentration of oxygen due to absence of circulation, resulting in a switch to anaerobic metabolism with the absence of the citric acid cycle. Anaerobic glycolysis resulted in the accumulation of lactic acid and an increase in the concentration of NADH.”
#Javan GT, Singh K, Finley SJ, Green RL and Sen CK (2024) Complexity of human death: its physiological, transcriptomic, and microbiological implications. Front. Microbiol.
http://frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2023.1345633/full
Quote: “Death results in massive biochemical changes in the body acutely caused by inadequacies in circulating oxygen. Such limitation results in a switch of metabolism from aerobic citric acid cycle to anaerobic (Sawyer et al., 1988). These biochemical changes lead to chemical indicators useful in accurately determining postmortem interval. For example, postmortem fall in blood pH is a result of accumulation of metabolites such as lactate (C3H5O3–) and formate (HCO2–) (Donaldson and Lamont, 2013). Furthermore, anaerobic glycolysis in postmortem tissue results in an increase in the concentration of NADH. Sawyer et al. (1988) demonstrated that cardiac blood taken from human remains after death becomes acidic (pH 7.0 to 5.5) by 20 h postmortem. In rat corpses cardiac blood pH dropped from 7.35 (antemortem) to 5.5 after 96 hrs postmortem (Sawyer et al., 1988).”
#Sacco MA, Aquila I. Post Mortem Molecular Biomarkers of Asphyxia: A Literature Review. International Journal of Molecular Sciences. 2024
https://www.mdpi.com/1422-0067/25/21/11607
Quote: “Lactate and pyruvate levels serve as crucial biochemical markers in the post mortem analysis of asphyxia. It is known that during hypoxia, the body shifts from aerobic to anaerobic metabolism, causing a significant rise in lactate levels [4].”
#Talley K, Alexov E. On the pH-optimum of activity and stability of proteins. Proteins. 2010
https://pmc.ncbi.nlm.nih.gov/articles/PMC2911520/
Quote: “Virtually every biological process is pH dependent reflecting the importance of the local pH on all processes in the cell. Thus, many biologically relevant effects are greatly influenced by the pH of the water phase including subcellular translocation 1, functional pH-dependence 2 and structural conformations associated with the function 3,4. The role of the concentration of hydrogen ions on protein stability is demonstrated by acidic/basic unfolding 5–8 and protein pH-dependent stability 9–14. Changes in pH are shown to trigger formation of amyloid fibers and aggregation 15–19. Protein-protein 20–22, protein-ligand 21,23,24, protein-membrane 25–28 and peptide-membrane 29 associations are greatly affected by the pH as well. pH is a significant factor for DNA-nanoparticles 30, DNA-metal ions 31,32 and DNA binding 33 interactions. It also plays an important role in pH-dependent drug optimization 34,35 and pH-dependent drug molecules aggregation 36. These examples demonstrate the crucial role of the pH of the water phase on the biological processes involving macromolecules and their assemblages.”
– Eventually either their energy reserves run out or too much acid accumulates, and their internal machinery breaks. Some are tiny sacks of digestive enzymes that dissolve anything organic.
This process is called “autolysis”. It is known to occur in humans postmortem, but much of the mechanistic details are drawn from animal studies.
#The Autopsy Book – Autolysis/Postmortem Histology. Retrieved April 2026.
https://theautopsybook.com/autolysis/
Quote: “The degree of postmortem autolysis varies among different tissues and organs, tending to be more pronounced in tissues with higher antemortem energy requirements (e.g., hepatocytes, proximal renal tubular epithelium) and less pronounced in tissues with lower antemortem energy requirements (e.g., lung, psoas muscle).
Organs such as the pancreas or mucosal surfaces of the gastrointestinal tract that contain or are exposed to proteolytic enzymes will demonstrate enhanced autolysis.
Keep in mind the “expected level” of autolysis that exists in the organ or tissue being examined. Once such an expectation is set, deviations from the background will likely reflect true pathology.
When juxtaposed, autolysis and necrosis often look different when viewed in the same field. Additionally, autolysis is a uniform process and so variations in degenerative change can suggest another process (such as necrosis, etc.)
Image: This liver demonstrates both antemortem necrosis (top arrow) and post-mortem autolysis (bottom arrow), each with distinct histologic appearance allowing them to be distinguished. (Image Credit: Alex Williamson).”
#Wenzlow N, Neal D, Stern AW, Prakoso D, Liu JJ, Delcambre GH, Beachboard S, Long MT. Feasibility of using tissue autolysis to estimate the postmortem interval in horses. J Vet Diagn Invest. 2021
https://journals.sagepub.com/doi/10.1177/10406387211021865
Quote: “Autolytic postmortem changes have been described in postmortem traumatized skeletal muscle in dogs17 and humans.7 Autolytic changes are not currently used by medical examiners to declare time since death in humans (personal communications). Importantly, to our knowledge, very limited work describes quantitatively the progression of the intensity and distribution of autolytic changes in any species.
[...] In general, most of the changes that we observed in the cerebrum were subtle and were not present in large percentages of the fields examined. Brain autolysis in humans showed neuronal Nissl substance dissolution, and karyorrhexis progressively increased from 5 to 22 h postmortem.12,14,15 Nissl substance dissolution in horses was only significant at 8°C, was seen as early as 1 h, and increased linearly until 72 h. Neuronal cytoplasmic vacuolation, basophilic cytoplasmic staining, and nuclear and cytoplasmic swelling were also considered to be autolytic changes in humans. In horses, neuronal nuclear swelling was only significant at 22°C; cytoplasmic swelling was only significant at 8°C, and neuronal cytoplasmic vacuolation was not statistically significant at either temperature. Autolytic changes in the human brain were first discernable as swelling of the neuronal nucleus and cytoplasm with increasing chromatolysis and liquefaction of the cytoplasm that may or may not involve the nucleus.14 These initial changes appeared at different times after death,11 with observations occurring as early as 30 min or as late at 3 h postmortem. Such chronology of events was not observed in equine brains; all autolytic changes in the brain were subtle, and no single most significant criterion stood out as a major marker of autolysis.
[...] After death, the blood supply to tissue compartments is compromised, causing acute hypoxic cell injuries that manifest as acute cellular swelling, hydropic and vacuolar degeneration, reduction in adenosine triphosphate (ATP), membrane damage, increased intracytoplasmic calcium, and formation of reactive oxygen species, all leading to cell death and initiation of autolysis (self-digestion).8,9 After death, this process of cell death is postmortem autolysis, the earliest step of decomposition, which is a process of denaturation of intracellular proteins and nucleic acid, protein coagulation, and enzymatic digestion of nuclei and cytoplasm (Table 1). Enzymes are released postmortem from the swollen lysosomes of dying cells by diffusion through the lysosomal membrane.9,11 More specifically, the enzymes driving autolysis are mostly phosphorus-rich enzymes including alkaline and acid phosphatases, ATP, 5′-nucleotidases, and glucose-6-phosphatase.11,18”
#Parisi F, Degl’Innocenti S, Aytaş Ç, Pirone A, Cantile C. Morphological and Immunohistochemical Changes in Progressive Postmortem Autolysis of the Murine Brain. Animals. 2024
https://www.mdpi.com/2076-2615/14/24/3676
Quote: “Postmortem autolysis is a common occurrence after death, marking the beginning of decomposition. The cessation of metabolic processes and the deprivation of oxygen trigger a series of events that result in cell death and self-digestion (autolysis) [1,2]. This process is primarily caused by the release of cathepsins and other hydrolases due to lysosome and peroxisome membrane permeabilization [3]. As oxygen levels decrease postmortem, anaerobic conditions develop, with anaerobic glycolysis providing energy for basic cellular functions. Waste products like carbon dioxide and lactate are released, causing a drop in cellular pH until the membrane loses its normal permeability, leading to cytoplasmic membrane disruption [4]. The term oncotic necrosis (or oncosis) is also proposed to describe the postmortem cell death pathway induced by the depletion of cellular adenosine triphosphate (ATP) [5]. Putrefaction then occurs as microorganisms, including bacteria, fungi, and protozoa from the gastrointestinal tract, degrade tissues, resulting in complete tissue decomposition.
Although autolysis and putrefaction can be distinguished on a molecular level, both processes can occur simultaneously to some degree in a decaying corpse [6]. However, autolytic changes are typically only detectable microscopically, whereas most postmortem changes resulting from putrefaction are visible macroscopically, and the decomposition byproducts may appear as gas, fluid, or salt form.
The histological identification of autolytic changes in various organs at varying postmortem intervals can enable forensic pathologists to more precisely determine the postmortem interval (PMI), thereby offering a clearer timeframe for the occurrence of death. While autolysis generally occurs simultaneously across the body, distinct cell types may exhibit varied responses to this process, influenced by their individual resistance to hypoxic conditions [2,7,8,9,10,11,12]. Organs such as the liver and brain, which are involved in the generation of high levels of ATP and membrane transport, are notably more prone to autolysis compared to other tissues [4]. The heart and kidney are moderately susceptible to the autolytic process in contrast to fibroblasts, which, due to their relatively scant lysosomes and lower levels of hydrolytic enzymes, exhibit significantly slower autolysis [13,14].”
#Weber K, Domènech A, Kegler K, Kreutzer R, Mayoral FJ, Okazaki Y, Ortega P, Polledo L, Razinger T, Richard OK, Sanchez R, Warfving N, Vallejo R and de Miguel R (2024) Onset and progression of postmortem histological changes in the central nervous system of RccHan™: WIST rats. Front. Vet. Sci.
https://www.frontiersin.org/journals/veterinary-science/articles/10.3389/fvets.2024.1378609/full
Quote: “Body decomposition is the result of two distinct processes: autolysis and putrefaction. Autolysis is the self-digestion of cells by the action of their own enzymes. Release and activation of these enzymes are consequences of disrupted cellular homeostasis and loss of cellular membrane integrity. It is mainly caused by the exhaustion of ATP and pH decrease related to the lack of oxygen, the failure of oxidative phosphorylation and the counterbalance activation of anerobic glycolysis. In some organs, autolysis creates the ideal conditions for bacterial proliferation leading to putrefaction (3).”
– As these sacs break open, the cells dissolve in a corrosive mix of acids and rogue enzymes. Their membranes break down, the cells swell up with water and burst, showering their neighbours with the same deadly mix of chemicals that killed them from the inside.
The cell “dissolving” here refers to a mixture of autolysis (= digestive enzymes spilling out of digestive organelles onto itself and neighborsíng cells) and a process called “necrosis”. Necrosis is the uncontrolled death of cells caused by extreme external factors such as e.g. sustained oxygen deprivation. The acid we’re mainly referring to here is lactic acid, a byproduct of metabolism in the absence of oxygen (anaerobic glycolysis). The “rogue enzymes” are digestive enzymes released from dying cells as part of autolysis.
#Khalid N, Azimpouran M. Necrosis Pathology. [Updated 2023 Mar 6]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2026 Jan-. Available from:
https://www.ncbi.nlm.nih.gov/books/NBK557627/
Quote: “Morphologically, necrotic cells characteristically demonstrate by swelling of organelles, such as the endoplasmic reticulum and mitochondria, the rupture of the plasma membrane, and the lysis of the cell.[17] These changes cause cells to be more eosinophilic, glassy, and vacuolated. Loss of cell membrane integrity and compromise of organelle membranes adds to this. ATP depletion or decreased synthesis is the first biochemical change observed in injury. ATP is produced by oxidative phosphorylation in mitochondria in the presence of oxygen. In necrosis associated with hypoxia or chemical injury, there is a lack of supply of oxygen to cells, leading to decreased ATP production. This lack of ATP results in the failure of the energy-dependent sodium pump in the plasma membrane, causing an influx of calcium and water, leading to cell swelling and detachment of ribosomes from the endoplasmic reticulum. Increased cytosolic calcium and oxidative stress lead to mitochondrial damage. Cytosolic calcium can also lead to the activation of several cytosolic enzymes, including phospholipases and proteases, which lead to the breakdown of both membranes(including lysosomal membranes) and proteins.”
#Donaldson AE, Lamont IL. Biochemistry changes that occur after death: potential markers for determining post-mortem interval. PLoS One. 2013
https://pmc.ncbi.nlm.nih.gov/articles/PMC3836773/
Quote: “Antemortem blood pH is regulated to stay within the narrow range of 7.35 to 7.45. If the blood pH is alkaline (greater than 7.45) or acidic (less than 7) this can lead to death [3] so blood pH is one of the most regulated systems in the body. Blood pH is regulated by acid-base buffers such as carbonic acid and biocarbonate ion, which exert their influence principally through the respiratory system and the kidneys in order to control the acid-base balance [3]. In death, the body buffering system is not maintained and blood pH changes can occur [4].
An early study reported that after death cardiac blood taken directly from 11 individual human remains showed a pH change from 7.0 to 5.5 by 20 hours post-mortem [5]. In the same study, blood collected from rat corpses showed a pH decrease from 7.35 at antemortem to 5.5 by 96 hours post-mortem.
[...] A lower blood pH must reflect the accumulation of acidic metabolites. Lactic acid is produced by lactate dehydrogenase from pyruvate via anaerobic glycolysis in skeletal muscle, liver and red blood cells when insufficient oxygen is available for pyruvate to enter the citric acid cycle. This process occurs naturally in muscle tissue during exercise and in normal metabolism inside red blood cells. The normal serum lactate concentration is 0.5-2.2 mmol.L-1. Circulating lactate is normally oxidised to pyruvate through the actions of lactate dehydrogenase (LDH) after being taken up by monocarboxylate transport proteins (MCTs) that are differentially expressed in actively respiring cells and tissues [6]. In the only recent study of lactate concentration in blood post-mortem, lactate in human heart blood increased 20-fold by one hour after death and 50-70 fold by 24 hours [2].
[...]
Figure 1. Blood pH. [A] In post-mortem blood from rat and pig corpses over 96 hours. The average pH of blood samples from five rat and two pig corpses at each time point are shown with standard deviations.
[...] Rat and pig blood in corpses showed a decrease in blood pH from 7.45 antemortem to 6.1 after 24 hours and to pH 5.1 after 96 hours. [...] The rapid decrease in blood pH in vivo (Figure 1 A) is most likely related to the accumulation of metabolites and ions such as bicarbonate, carbon dioxide, hydrogen ions, di-hydrogen phosphate ions, and lactic acid building up in a corpse due to autolysis, which does not occur in vitro.
[...] In the in vivo experiments, (Figure 2 A) lactate concentration rose rapidly from between 0.5 and 2.5 mmol.L-1 immediately post-mortem to between 3 and 7.5 mmol.L-1 by three hours post-mortem.
Figure 2. Concentration of lactate. [A] In post-mortem blood from rat and pig corpses over 96 hours. The average lactate concentration and the standard deviations in blood from seven rats and two pigs at each time point are shown.”
#WR Sawyer, DR Steup, BS Martin, RB Forney; Cardiac Blood pH as a Possible Indicator of Postmortem Interval. J. Forensic Sci. 1 November 1988
#Javan GT, Singh K, Finley SJ, Green RL and Sen CK (2024) Complexity of human death: its physiological, transcriptomic, and microbiological implications. Front. Microbiol. 14:1345633.
http://frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2023.1345633/full
Quote: “Death results in massive biochemical changes in the body acutely caused by inadequacies in circulating oxygen. Such limitation results in a switch of metabolism from aerobic citric acid cycle to anaerobic (Sawyer et al., 1988). These biochemical changes lead to chemical indicators useful in accurately determining postmortem interval. For example, postmortem fall in blood pH is a result of accumulation of metabolites such as lactate (C3H5O3–) and formate (HCO2–) (Donaldson and Lamont, 2013). Furthermore, anaerobic glycolysis in postmortem tissue results in an increase in the concentration of NADH. Sawyer et al. (1988) demonstrated that cardiac blood taken from human remains after death becomes acidic (pH 7.0 to 5.5) by 20 h postmortem. In rat corpses cardiac blood pH dropped from 7.35 (antemortem) to 5.5 after 96 hrs postmortem (Sawyer et al., 1988).”
#Parisi F, Degl’Innocenti S, Aytaş Ç, Pirone A, Cantile C. Morphological and Immunohistochemical Changes in Progressive Postmortem Autolysis of the Murine Brain. Animals. 2024
https://www.mdpi.com/2076-2615/14/24/3676
Quote: “Postmortem autolysis is a common occurrence after death, marking the beginning of decomposition. The cessation of metabolic processes and the deprivation of oxygen trigger a series of events that result in cell death and self-digestion (autolysis) [1,2]. This process is primarily caused by the release of cathepsins and other hydrolases due to lysosome and peroxisome membrane permeabilization [3]. As oxygen levels decrease postmortem, anaerobic conditions develop, with anaerobic glycolysis providing energy for basic cellular functions. Waste products like carbon dioxide and lactate are released, causing a drop in cellular pH until the membrane loses its normal permeability, leading to cytoplasmic membrane disruption [4].”
#Weber K, Domènech A, Kegler K, Kreutzer R, Mayoral FJ, Okazaki Y, Ortega P, Polledo L, Razinger T, Richard OK, Sanchez R, Warfving N, Vallejo R and de Miguel R (2024) Onset and progression of postmortem histological changes in the central nervous system of RccHan™: WIST rats. Front. Vet. Sci.
https://www.frontiersin.org/journals/veterinary-science/articles/10.3389/fvets.2024.1378609/full
Quote: “Body decomposition is the result of two distinct processes: autolysis and putrefaction. Autolysis is the self-digestion of cells by the action of their own enzymes. Release and activation of these enzymes are consequences of disrupted cellular homeostasis and loss of cellular membrane integrity. It is mainly caused by the exhaustion of ATP and pH decrease related to the lack of oxygen, the failure of oxidative phosphorylation and the counterbalance activation of anerobic glycolysis. In some organs, autolysis creates the ideal conditions for bacterial proliferation leading to putrefaction (3).”
#Wenzlow N, Neal D, Stern AW, Prakoso D, Liu JJ, Delcambre GH, Beachboard S, Long MT. Feasibility of using tissue autolysis to estimate the postmortem interval in horses. J Vet Diagn Invest. 2021
https://journals.sagepub.com/doi/10.1177/10406387211021865
Quote: “After death, the blood supply to tissue compartments is compromised, causing acute hypoxic cell injuries that manifest as acute cellular swelling, hydropic and vacuolar degeneration, reduction in adenosine triphosphate (ATP), membrane damage, increased intracytoplasmic calcium, and formation of reactive oxygen species, all leading to cell death and initiation of autolysis (self-digestion).8,9 After death, this process of cell death is postmortem autolysis, the earliest step of decomposition, which is a process of denaturation of intracellular proteins and nucleic acid, protein coagulation, and enzymatic digestion of nuclei and cytoplasm (Table 1). Enzymes are released postmortem from the swollen lysosomes of dying cells by diffusion through the lysosomal membrane.9,11 More specifically, the enzymes driving autolysis are mostly phosphorus-rich enzymes including alkaline and acid phosphatases, ATP, 5′-nucleotidases, and glucose-6-phosphatase.11,18”
– At the same time, the severe energy depletion has reached your muscles. Paradoxically, they can’t relax anymore. The fibers within them need energy to let each other go and now they lock up. Starting in your eyelids, jaw and neck, a wave of stiffening works its way through your body, turning meat to stone.
#Shedge R, Krishan K, Warrier V, et al. Postmortem Changes. [Updated 2023 Jul 24]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2026 Jan-. Available from:
https://www.ncbi.nlm.nih.gov/books/NBK539741/
Quote: “Rigor mortis is the post mortem stiffening/ rigidity of the body. It results from a decrease in levels of adenosinetriphosphate (ATP) beyond critical levels. When a person dies, calcium ions flood muscle fibers due to the loss of integrity of the muscle cells. These ions cause the binding of actin and myosin filaments, causing contraction. Relaxation of muscles is achieved by ATP driven pumping of the calcium ions back into the sarcoplasmic reticulum of the muscle cells. As a result of the lack of ATP, the muscles fail to relax, and the actinomyosin complex created during the contraction stays intact; this causes the muscles to become hard and rigid.[20][21][22] Rigor mortis first appears in the involuntary muscles of the heart, and apparently follows proximal to distal progression. It is observed in eyelids, followed by the neck, lower jaw, chest, upper limbs, abdomen, lower limbs, and then finally in the fingers and toes. Rigor mortis appears in 1 to 2 hours after death, is completely formed 12 hours after death, is sustained for the next 12 hours, and vanishes over the next 12 hours, sometimes referred to as the ‘march of rigor.’”
– Even the tiny muscles around your hair follicles lock up, giving you your final goose bumps.
#Shedge R, Krishan K, Warrier V, et al. Postmortem Changes. [Updated 2023 Jul 24]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2026 Jan-. Available from:
https://www.ncbi.nlm.nih.gov/books/NBK539741/
Quote: “The effect of rigor on individual muscles can be of additional significance. The rigor of erector pilae muscles may cause elevation of hair leading to the pimpled appearance of the skin. This phenomenon is termed ‘cutis anserina’ or ‘goose skin.’”
– Your most important muscle – your heart – is forced to slowly contract one final time.
#Shedge R, Krishan K, Warrier V, et al. Postmortem Changes. [Updated 2023 Jul 24]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2026 Jan-. Available from:
https://www.ncbi.nlm.nih.gov/books/NBK539741/
Quote: “In the heart, rigor causes contraction of ventricles, which may be erroneously interpreted as ventricular hypertrophy.”
– A sad echo of your heartbeat as your blood turns deeply acidic.
#Javan GT, Singh K, Finley SJ, Green RL and Sen CK (2024) Complexity of human death: its physiological, transcriptomic, and microbiological implications. Front. Microbiol. 14:1345633.
http://frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2023.1345633/full
Quote: “Death results in massive biochemical changes in the body acutely caused by inadequacies in circulating oxygen. Such limitation results in a switch of metabolism from aerobic citric acid cycle to anaerobic (Sawyer et al., 1988). These biochemical changes lead to chemical indicators useful in accurately determining postmortem interval. For example, postmortem fall in blood pH is a result of accumulation of metabolites such as lactate (C3H5O3–) and formate (HCO2–) (Donaldson and Lamont, 2013). Furthermore, anaerobic glycolysis in postmortem tissue results in an increase in the concentration of NADH. Sawyer et al. (1988) demonstrated that cardiac blood taken from human remains after death becomes acidic (pH 7.0 to 5.5) by 20 h postmortem. In rat corpses cardiac blood pH dropped from 7.35 (antemortem) to 5.5 after 96 hrs postmortem (Sawyer et al., 1988).”
#Donaldson AE, Lamont IL. Biochemistry changes that occur after death: potential markers for determining post-mortem interval. PLoS One. 2013
https://pmc.ncbi.nlm.nih.gov/articles/PMC3836773/
Quote: “Antemortem blood pH is regulated to stay within the narrow range of 7.35 to 7.45. If the blood pH is alkaline (greater than 7.45) or acidic (less than 7) this can lead to death [3] so blood pH is one of the most regulated systems in the body. Blood pH is regulated by acid-base buffers such as carbonic acid and biocarbonate ion, which exert their influence principally through the respiratory system and the kidneys in order to control the acid-base balance [3]. In death, the body buffering system is not maintained and blood pH changes can occur [4].
An early study reported that after death cardiac blood taken directly from 11 individual human remains showed a pH change from 7.0 to 5.5 by 20 hours post-mortem [5]. In the same study, blood collected from rat corpses showed a pH decrease from 7.35 at antemortem to 5.5 by 96 hours post-mortem.
[...] A lower blood pH must reflect the accumulation of acidic metabolites. Lactic acid is produced by lactate dehydrogenase from pyruvate via anaerobic glycolysis in skeletal muscle, liver and red blood cells when insufficient oxygen is available for pyruvate to enter the citric acid cycle. This process occurs naturally in muscle tissue during exercise and in normal metabolism inside red blood cells. The normal serum lactate concentration is 0.5-2.2 mmol.L-1. Circulating lactate is normally oxidised to pyruvate through the actions of lactate dehydrogenase (LDH) after being taken up by monocarboxylate transport proteins (MCTs) that are differentially expressed in actively respiring cells and tissues [6]. In the only recent study of lactate concentration in blood post-mortem, lactate in human heart blood increased 20-fold by one hour after death and 50-70 fold by 24 hours [2].
[...]
Figure 1. Blood pH. [A] In post-mortem blood from rat and pig corpses over 96 hours. The average pH of blood samples from five rat and two pig corpses at each time point are shown with standard deviations.
[...] Rat and pig blood in corpses showed a decrease in blood pH from 7.45 antemortem to 6.1 after 24 hours and to pH 5.1 after 96 hours. [...] The rapid decrease in blood pH in vivo (Figure 1 A) is most likely related to the accumulation of metabolites and ions such as bicarbonate, carbon dioxide, hydrogen ions, di-hydrogen phosphate ions, and lactic acid building up in a corpse due to autolysis, which does not occur in vitro.
[...] In the in vivo experiments, (Figure 2 A) lactate concentration rose rapidly from between 0.5 and 2.5 mmol.L-1 immediately post-mortem to between 3 and 7.5 mmol.L-1 by three hours post-mortem.
Figure 2. Concentration of lactate. [A] In post-mortem blood from rat and pig corpses over 96 hours. The average lactate concentration and the standard deviations in blood from seven rats and two pigs at each time point are shown.”
#WR Sawyer, DR Steup, BS Martin, RB Forney; Cardiac Blood pH as a Possible Indicator of Postmortem Interval. J. Forensic Sci. 1 November 1988
– Your body, mostly your gut, hosts roughly 30 trillion bacteria.
#Sender R, Fuchs S, Milo R (2016) Revised Estimates for the Number of Human and Bacteria Cells in the Body. PLOS Biology 14(8): e1002533
https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1002533
Quote: “Reported values in the literature on the number of cells in the body differ by orders of magnitude and are very seldom supported by any measurements or calculations. Here, we integrate the most up-to-date information on the number of human and bacterial cells in the body. We estimate the total number of bacteria in the 70 kg "reference man" to be 3.8·1013. For human cells, we identify the dominant role of the hematopoietic lineage to the total count (≈90%) and revise past estimates to 3.0·1013 human cells. Our analysis also updates the widely-cited 10:1 ratio, showing that the number of bacteria in the body is actually of the same order as the number of human cells, and their total mass is about 0.2 kg.”
#Kho ZY and Lal SK (2018) The Human Gut Microbiome – A Potential Controller of Wellness and Disease. Front. Microbiol. 9:1835.
https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2018.01835/full
Quote: “The human microbiome comprises of collective genomes of microbiota inhabiting us, namely protozoa, archaea, eukaryotes, viruses and predominantly bacteria that live symbiotically on and within various sites of the human body. Examples of occupied habitats include our oral cavity, genital organs, respiratory tract, skin and gastrointestinal system (Lloyd-Price et al., 2016). The human microbiota is estimated to be ∼1013–1014 microbial cells, with around 1:1 microbial cells to human cells ratio (Sender et al., 2016). These numbers are derived from the total bacterial cells in colon (3.8 × 1013 bacteria), the organ that harbors the densest number of microbes (Sender et al., 2016).”
– Friendly symbionts that break down fibers, produce vitamins, or keep hostile bacteria in check.
#Valdes A M, Walter J, Segal E, Spector T D. Role of the gut microbiota in nutrition and health BMJ 2018; 361 :k2179
https://www.bmj.com/content/361/bmj.k2179
Quote: “The gut microbiota provides essential capacities for the fermentation of non-digestible substrates like dietary fibres and endogenous intestinal mucus. This fermentation supports the growth of specialist microbes that produce short chain fatty acids (SCFAs) and gases.17 The major SCFAs produced are acetate, propionate, and butyrate.”
#Tarracchini C, Lugli GA, Mancabelli L, van Sinderen D, Turroni F, Ventura M, Milani C. 2024. Exploring the vitamin biosynthesis landscape of the human gut microbiota.
https://journals.asm.org/doi/10.1128/msystems.00929-24
Quote: “The human gut microbiota possesses the capacity to synthesize vitamins, especially B group vitamins, which are recognized as indispensable for various biological processes both among members of these bacterial communities and host cells. Accordingly, vitamin production by intestinal commensals has attracted significant interest.”
#Spragge F, Bakkeren E, Jahn MT, B N Araujo E, Pearson CF, Wang X, Pankhurst L, Cunrath O, Foster KR. Microbiome diversity protects against pathogens by nutrient blocking. Science. 2023 Dec 15;382(6676):eadj3502.
https://pmc.ncbi.nlm.nih.gov/articles/PMC7616675/
Quote: “The human gut is home to diverse bacterial species collectively known as the gut microbiota. A major health benefit provided by the gut microbiota is protection against pathogen colonization and subsequent infection; a phenomenon known as colonization resistance (1). The ability of the microbiota to protect against numerous enteric pathogens is well-documented, with evidence that particular species within the microbiota play a more important role than others (2–9). The ways that colonization resistance can arise include competition for nutrients and space, direct antagonism by toxins and other harmful compounds, and promoting host immunity against pathogens (1, 10, 11).”
– But they are not actually your friends.
Gut microbes can benefit us while we are alive, and we also exert a lot of control over them to prevent them from leaving the gut. They are not intrinsically evolved to “help” us, they live in us because it benefits them. Once we are dead, we cannot control them anymore and they will happily eat us alive from within.
#Jacob Wilde et al. ,Host control of the microbiome: Mechanisms, evolution, and disease.Science 385. eadi3338 (2024).
https://www.science.org/doi/10.1126/science.adi3338
Quote: “The many potential benefits of a microbiome—the microbiota plus associated host factors—can foster the view that humans harbor an intrinsically helpful ecosystem in their gut that is regulated primarily by diet. In reality, members of the microbiota face chronic competition for resources and physical positioning in an environment where large numbers of cells are expelled each day. Immigration of new strains, alongside rapid and shortsighted microbial evolution, poses the continual threat of symbionts that grow rapaciously but harm the host, including pathogens and “cheater” genotypes that invest in their own growth rather than benefiting the host. In response to this pressure, hosts have evolved a wide range of control mechanisms that continually monitor and manipulate their symbionts to limit harm and promote the benefits received. Examples such as the human microbiome, therefore, can be conceptualized as “an ecosystem on a leash,” where symbionts interact in diverse ecological communities that are strongly shaped by host control.”
– All these microbes are strictly confined behind the gut lining, held off by a physical wall and immune cells. But an hour after your heart stopped this border is crumbling.
The gut lining or intestinal epithelial barrier is the “wall” between the gut microbiome and the rest of the body. To prevent gut microbes and pathogens from invading the body, but still let nutrients through, the barrier engages in a ton of different biological processes, all of which take energy. After death and the loss of oxygen and therefore energy (ATP) in the body, these processes fail and the wall becomes “traversable” by microbes.
#Garavaglia, Beatrice & Vallino, Letizia & Amoruso, Angela & Pane, Marco & Ferraresi, Alessandra & Isidoro, Ciro. (2024). The Role of Gut Microbiota, Immune System, and Autophagy in the Pathogenesis of Inflammatory Bowel Disease: Molecular Mechanisms and Therapeutic Approaches. Aspects of Molecular Medicine. 4. 100056.
https://www.sciencedirect.com/science/article/pii/S2949688824000236
Quote: “The intestinal epithelial barrier plays a pivotal role in preserving the delicate balance between defense mechanisms and symbiotic interaction within the gut. Beyond its primary role in processing and absorbing food and nutrients, the intestinal epithelial barrier acts as biochemical and physical barrier against pathogens, toxins, and dietary antigens, establishing a primary defense line from the contents of the gut lumen. Simultaneously, it creates the proper microenvironment, preventing excessive colonization of commensal bacteria in the luminal compartment and facilitating the harmonious interaction between the host and the microbiota (Peterson and Artis, 2014).
[...] Mucin proteins produced by these cells create a gel-like structure that serves as the first line of defense against bacteria and inflammation in the intestine, preventing direct contact between the gut lumen and epithelial cells. This structure provides an adhesion substrate for the microbiota niche and simultaneously impedes the transepithelial invasion of microorganisms into the systemic circulation (Schroeder, 2019).”
#Shedge R, Krishan K, Warrier V, et al. Postmortem Changes. [Updated 2023 Jul 24]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2026 Jan-. Available from:
https://www.ncbi.nlm.nih.gov/books/NBK539741/
Quote: “Putrefaction is the decomposition of the body carried out by the microbial action. After cessation of homeostasis, the natural flora of the body migrates from the gut to the blood vessels and spreads all over the body. External micro-organisms enter the body through the alimentary canal, respiratory tract, and open wounds. In the absence of body defenses/immune mechanisms, the microbes keep growing, as they feed upon the proteins and carbohydrates of the blood and body parts. The principal bacterial agent causing putrefaction is the gram-positive, anaerobic, and rod-shaped Clostridium welchii.[33] It releases lecithinase, which causes hydrolysis of lecithin present in the blood cells, causing their lysis. Putrefaction begins within an hour of death, but the peak activity of the microbes occurs around the 24-hour timeframe.”
– Your body is carbs, fats and proteins. Food. First millions, then billions break out of your intestines, through the apocalyptic highways of your lymphatic system and acid filled blood vessels.
The microbial degradation of the dead body is called “putrefaction”. It is known to occur in humans, but some mechanistic details are extrapolated from animal studies.
#Shedge R, Krishan K, Warrier V, et al. Postmortem Changes. [Updated 2023 Jul 24]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2026 Jan-. Available from:
https://www.ncbi.nlm.nih.gov/books/NBK539741/
Quote: “Putrefaction is the decomposition of the body carried out by the microbial action. After cessation of homeostasis, the natural flora of the body migrates from the gut to the blood vessels and spreads all over the body. External micro-organisms enter the body through the alimentary canal, respiratory tract, and open wounds. In the absence of body defenses/immune mechanisms, the microbes keep growing, as they feed upon the proteins and carbohydrates of the blood and body parts. The principal bacterial agent causing putrefaction is the gram-positive, anaerobic, and rod-shaped Clostridium welchii.[33] It releases lecithinase, which causes hydrolysis of lecithin present in the blood cells, causing their lysis. Putrefaction begins within an hour of death, but the peak activity of the microbes occurs around the 24-hour timeframe.”
#Heimesaat MM, Boelke S, Fischer A, Haag LM, Loddenkemper C, et al. (2012) Comprehensive Postmortem Analyses of Intestinal Microbiota Changes and Bacterial Translocation in Human Flora Associated Mice. PLOS ONE 7(7): e40758.
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0040758
Quote: “The highest rates of culture-positive samples were assessed in mesenteric lymph nodes (MLNs) of SPF mice. Of note, already within 5 min p.m. more than 50% of MLNs were culture-positive due to translocated lactobacilli. Until 30 min p.m. the detection rate increased up to >75% followed by a decrease to approximately 40% at 1 hours p.m., and another subsequent increase thereafter. At 12 hours, 100% of MLNs were culture-positive due to translocation of multiple bacterial species originated from the murine intestine such as E. coli, enterococci, Bacteroides/Prevotella spp., clostridia, and - with the highest detection rate - lactobacilli (Fig. 3A). Interestingly, at 1 h p.m., bacterial translocation rates were lowest in all investigated compartments (Fig. 3) with virtually no bacterial growth in spleen, liver, kidney, and blood (Fig. 3 B–E). Furthermore, a bi-phasic detection pattern could be observed: 15–50% of samples derived from MLNs, spleen, liver, kidney, and blood were culture-positive until 30 min p.m., followed by a decline of positivity rates at 1 h, whereas thereafter the rates of culture-positive organs increased to maximum levels of >80% at 48 and 72 hours p.m. (Fig. 3). Again, the most frequently detected species were lactobacilli until 3 hours p.m. Thereafter the complexity of detected species increased up to 4–5 different bacterial groups (Fig. 3 B–D). Strikingly, already within 5 min p.m., 25% of blood cultures were positive for enterococci, lactobacilli, and/or Bacteroides/Prevotella spp. (Fig. 3E). At 72 hours postmortem all cardiac blood samples were culture-positive for E. coli (100%), enteroccci (75%) and lactobacilli (62.5%).”
– Your microbiome turns into your necrobiome.
The necrobiome is the community of microbes associated with a dead organism. The former internal microbiome is a big part of it, but it is later also joined by external microbes. Together, they form the necrobiome.
#M. E. Benbow, P. S. Barton, M. D. Ulyshen, J. C. Beasley, T. L. DeVault, M. S. Strickland, J. K. Tomberlin, H. R. Jordan, and J. L. Pechal. 2019. Necrobiome framework for bridging decomposition ecology of autotrophically and heterotrophically derived organic matter. Ecological Monographs89(1):e01331.
Quote: “Decomposition contributes to global ecosystem function by contributing to nutrient recycling, energy flow, and limiting biomass accumulation. The decomposer organisms influencing this process form diverse, complex, and highly dynamic communities that often specialize on different plant or animal resources. Despite performing the same net role, there is a need to conceptually synthesize information on the structure and function of decomposer communities across the spectrum of dead plant and animal resources. A lack of synthesis has limited cross-disciplinary learning and research in important areas of ecosystem and community ecology. Here we expound on the “necrobiome” concept and develop a framework describing the decomposer communities and their interactions associated with plant and animal resource types within multiple ecosystems. We outline the biotic structure and ecological functions of the necrobiome, along with how the necrobiome fits into a broader landscape and ecosystem context. The expanded necrobiome model provides a set of perspectives on decomposer communities across resource types, and conceptually unifies plant and animal decomposer communities into the same framework, while acknowledging key differences in processes and mechanisms. This framework is intended to raise awareness among researchers, and advance the construction of explicit, mechanistic hypotheses that further our understanding of decomposer community contributions to biodiversity, the structure and function of ecosystems, global nutrient recycling and energy flow.
[...]
The necrobiome is the community of organisms associated with necromass decomposition and includes their interactions with the necromass, with each other, and with their surrounding habitat and ecosystem. This concept is general across plant, fungi, dung/frass/feces, or animal necromass types, and in both terrestrial and aquatic realms. (a) Various qualities of necromass have strong controlling effects on its associated necrobiome. (b) The decomposing necromass is host to a microbiome while alive, both internal (endonecrotic) and external (epinecrotic), and these communities begin to change after death and during the course of decomposition. The changing microbiomes use the organic matter as habitat and for energy and nutrients. As decay progresses, the organic matter and associated activities of the microbes facilitate the attraction of invertebrate and vertebrate saprophages that directly consume the necromass and the microbial communities. (c) All of these biotic components of the necrobiome interact in ways that give rise to pathways of microbial and elemental dispersal away from the decaying necromass into adjacent soil or water media, as well as to the surrounding ecosystem at both localized and broad spatial scales. (d) The necrobiome and its functions operate within a complex network of interactions that are constrained by its terrestrial or aquatic context, the regional species pool, and gradients of abiotic factors. Critically, all these aspects of the necrobiome are interlinked, and the relative importance of each component of the necrobiome, and their function, will depend on the intrinsic qualities of decaying necromass and the extrinsic controlling environmental factors (e.g., temperature, moisture, latitude).”
– But hold on, there's still resistance within your body! The last remnants of your immune system are desperately fighting back! Built to thrive in the most extreme, oxygen-starved regions of your body, your immune cells survive long after you have stopped breathing.
The timeline of survival differs between immune cell types, bodies and how the bodies were stored. But relatively speaking, lymphocytes (a type of white blood cells) tend to be some of the cell types that survive the longest among the immune cells after death of the body. Why they are so resistant is not entirely understood, but it is likely due to the lack of enzymes within them, which slows visible autolysis when oxygen runs out, and also their relative tolerance of low-oxygen conditions, which they would naturally encounter in places like the bone marrow.
#Dokgöz H, Arican N, Elmas I, Fincanci SK. Comparison of morphological changes in white blood cells after death and in vitro storage of blood for the estimation of postmortem interval. Forensic Sci Int. 2001 Dec 15;124(1):25-31.
https://www.sciencedirect.com/science/article/abs/pii/S037907380100559X?via%3Dihub
Quote: “In this study, in vitro storage and postmortem changes of white blood cells were aimed to be compared within the given postmortem interval, and a follow-up study was carried out. Blood smears which were obtained from 10 non-refrigerated cadavers (experimental group) and from 40 hospital patients (control group) have been evaluated to observe and compare changes during the in vitro storage and postmortem degenerative morphological changes that white blood cells undergo throughout the given postmortem intervals. The samples were examined by using a light microscope, and blood cells were differentiated by staining blood films with May–Grunwald stain, followed by Giemsa stain. Identifiable degenerated eosinophils and monocytes were first examined at 6 h of death and the in vitro storage, and they were unidentifiable beyond 72 h of storage. Identifiable degeneration of neutrophils were first examined at 6 h of death and storage while unidentifiable beyond 96 h of storage. Identifiable degeneration of lymphocytes were first examined at 24 h of death, and they were still identifiable beyond 120 h.”
#Choudhury A, Mahanta A. Estimation of Time Since Death From Morphological Changes Occurring in White Blood Cells After Death. Cureus. 2025
https://pmc.ncbi.nlm.nih.gov/articles/PMC12421351/
Quote: “At a PMI between 24 and 36 hours, neutrophils appeared grossly dysmorphic with nuclear pyknosis and fragmentation and cytoplasmic vacuolation, the cell membrane was intact, eosinophils were grossly dysmorphic with cell membrane breakdown occurring in <50% of observed cells but were still identifiable, monocytes showed nuclear pyknosis and fragmentation in >50% of the observed cells but cytoplasmic vacuolation was seen in <50% of the observed cells, and lymphocytes showed nuclear pyknosis in <50% of the observed cells. At a PMI between 36 and 48 hours, the neutrophils showed disintegration of the cell membrane but were still identifiable, the eosinophils were not identifiable on the smears examined, the monocytes were grossly dysmorphic with nuclear pyknosis, fragmentation, and cytoplasmic vacuolation in >50% of observed cells, the cell membrane was intact, and lymphocytes showed nuclear pyknosis in >50% of the observed cells with nuclear fragmentation in <50% cells. At a PMI between 48 and 72 hours, the neutrophils were no longer identifiable on the smears examined; the eosinophils were no longer identifiable, the monocytes started showing breakdown of the cell membrane but were still identifiable, and lymphocytes showed gross nuclear abnormalities in the form of pyknosis and fragmentation in >50% of cells observed. At a PMI between 72 and 96 hours, the neutrophils and eosinophils were no longer identifiable, the monocytes were no longer identifiable, the lymphocytes were grossly dysmorphic with nuclear pyknosis, fragmentation, and cytoplasmic vacuolation seen in >50% of the observed cells, and the cell membrane was intact. At a PMI between 96 and 120 hours, the neutrophils, eosinophils, and monocytes were no longer identifiable, and lymphocytes showed breakdown of the cell membrane but were still identifiable. Beyond 120 hours, lymphocytes could no longer be identified on smears.”
#Boothby, M., Cho, S.H. (2024). Hypoxia and the Hypoxia-Inducible Factors in Lymphocyte Differentiation and Function. In: Borggrefe, T., Giaimo, B.D. (eds) Transcription factors in blood cell development. Advances in Experimental Medicine and Biology, vol 1459. Springer, Cham.
https://link.springer.com/chapter/10.1007/978-3-031-62731-6_6
Quote: “Molecular oxygen doubles as a biomolecular building block and an element required for energy generation and metabolism in aerobic organisms. A variety of systems in mammalian cells sense the concentration of oxygen to which they are exposed and are tuned to the range present in our blood and tissues. The ability to respond to insufficient O2 in tissues is central to regulation of erythroid lineage cells, but challenges also are posed for immune cells by a need to adjust to very different oxygen concentrations. Hypoxia-inducible factors (HIFs) provide a major means of making such adjustments. For adaptive immunity, lymphoid lineages are initially defined in bone marrow niches; T lineage cells arise in the thymus, and B cells complete maturation in the spleen. Lymphocytes move from these first stops into microenvironments (bloodstream, lymphatics, and tissues) with distinct oxygenation in each. Herein, evidence pertaining to functions of the HIF transcription factors (TFs) in lymphocyte differentiation and function is reviewed. For the CD4+ and CD8+ subsets of T cells, the case is very strong that hypoxia and HIFs regulate important differentiation events and functions after the naïve lymphocytes emerge from the thymus. In the B lineage, the data indicate that HIF1 contributes to a balanced regulation of B-cell fates after antigen (Ag) activation during immunity. A model synthesized from the aggregate literature is that HIF in lymphocytes generally serves to modulate function in a manner dependent on the molecular context framed by other TFs and signals.”
#McNamee, E.N., Korns Johnson, D., Homann, D. et al. Hypoxia and hypoxia-inducible factors as regulators of T cell development, differentiation, and function. Immunol Res 55, 58–70 (2013).
https://link.springer.com/article/10.1007/s12026-012-8349-8
Quote: “Oxygen is a molecule that is central to cellular respiration and viability, yet there are multiple physiologic and pathological contexts in which cells experience conditions of insufficient oxygen availability, a state known as hypoxia. Given the metabolic challenges of a low oxygen environment, hypoxia elicits a range of adaptive responses at the cellular, tissue, and systemic level to promote continued survival and function. Within this context, T lymphocytes are a highly migratory cell type of the adaptive immune system that frequently encounters a wide range of oxygen tensions in both health and disease. It is now clear that oxygen availability regulates T cell differentiation and function, a response orchestrated in large part by the hypoxia-inducible factor transcription factors. Here, we discuss the physiologic scope of hypoxia and hypoxic signaling, the contribution of these pathways in regulating T cell biology, and current gaps in our understanding. Finally, we discuss how emerging therapies that modulate the hypoxic response may offer new modalities to alter T cell function and the outcome of acute and chronic pathologies.”
– Without blood flowing, their communication with each other is lost, their once mighty army is scattered across your giant body. Soldiers call for backup and for help, but their signals don’t travel.
Immune cells need to move through circulation (blood flow) to work properly, and their signals to each other and to other parts of the body travel through blood as well. In death, blood flow stops, and so the cells and signals don't travel much anymore beyond “crawling”, i.e. the motility of individual cells. This is extremely slow (micrometers per min) compared to blood flow (km/h).
#Song B, Guo W, He Y, Yao X, Sun J, Wang S. Targeting immune cell migration as therapy for inflammatory disease: a review. Front Immunol. 2025
https://pmc.ncbi.nlm.nih.gov/articles/PMC12507636/
Quote: “Immune cell migration plays a pivotal role in coordinating inflammatory responses and maintaining immune surveillance. Here, we provide a comprehensive overview of the migratory behaviors of key immune cell subsets, including Th1, Th2, regulatory T cells, macrophages, dendritic cells, and neutrophils and the molecular mechanisms that guide their trafficking from lymphoid organs to inflamed tissues. We highlight the stepwise migration cascade: priming in secondary lymphoid organs, trafficking through blood vessels, adhesion to endothelium, and extravasation into tissues. Each step is critically regulated by chemokines, selectins, integrins, and proteases.”
#Vesperini D, Montalvo G, Qu B, Lautenschläger F. Characterization of immune cell migration using microfabrication. Biophys Rev. 2021
https://pmc.ncbi.nlm.nih.gov/articles/PMC8285443/
Quote: “In vivo, immune cells mostly use the amoeboid mode of motility. The migration speed of immune cells is not constant, but varies between fast (~20 μm/min) and slow (<1 μm/min) migration phases (Chabaud et al. 2015).”
– And so they fight a lonely last stand. Micro-battles, imperceptible even just a millimeter away.
Alive and active/functional immune cells can be isolated from dead bodies up to 14 hours after death. In the study below, they stopped measuring after 14 hours, so it is possible that the immune cells would survive even longer.
#Ahimbisibwe G, Nakibuule M, Martin Ssejoba M, Oyamo D, Mulwana R, Nabulime J, Babirye F, Kizito MA, Lekuya HM, Adakun AS, Nalumansi D, Muryasingura S, Lukande R, Kyazze A, Baluku JB, Biraro IA, Cose S. Feasibility and acceptability of undertaking postmortem studies for tuberculosis medical research in a low income country. Front Immunol. 2023.
https://pmc.ncbi.nlm.nih.gov/articles/PMC10734300/
Quote: “Introduction
If we are to break new ground in difficult-to-treat or difficult-to-vaccinate diseases (such as HIV, malaria, or tuberculosis), we must have a better understanding of the immune system at the site of infection in humans. For tuberculosis (TB), the initial site of infection is the lungs, but obtaining lung tissues from subjects suffering from TB has been limited to bronchoalveolar lavage (BAL) or sputum sampling, or surgical resection of diseased lung tissue.
Methods
We examined the feasibility of undertaking a postmortem study for human tuberculosis research at Mulago National Referral Hospital in Kampala, Uganda.
Results
Postmortem studies give us an opportunity to compare TB-involved and -uninvolved sites, for both diseased and non-diseased individuals. We report good acceptability of the next-of-kin to consent for their relative’s tissue to be used for medical research; that postmortem and tissue processing can be undertaken within 8 hours following death; and that immune cells remain viable and functional up to 14 hours after death.
Discussion
Postmortem procedures remain a valuable and essential tool both to establish cause of death, and to advance our medical and scientific understanding of infectious diseases.”
– Until their exhausted little bodies can’t go on anymore. After 24 hours your last immune cell finally dies.
After roughly 24 hours, immune cells appear grossly degraded in cadavers and are most likely not functional anymore. The exact timeline likely varies from body to body.
#Choudhury A, Mahanta A. Estimation of Time Since Death From Morphological Changes Occurring in White Blood Cells After Death. Cureus. 2025
https://pmc.ncbi.nlm.nih.gov/articles/PMC12421351/
Quote: “At a PMI between 24 and 36 hours, neutrophils appeared grossly dysmorphic with nuclear pyknosis and fragmentation and cytoplasmic vacuolation, the cell membrane was intact, eosinophils were grossly dysmorphic with cell membrane breakdown occurring in <50% of observed cells but were still identifiable, monocytes showed nuclear pyknosis and fragmentation in >50% of the observed cells but cytoplasmic vacuolation was seen in <50% of the observed cells, and lymphocytes showed nuclear pyknosis in <50% of the observed cells. At a PMI between 36 and 48 hours, the neutrophils showed disintegration of the cell membrane but were still identifiable, the eosinophils were not identifiable on the smears examined, the monocytes were grossly dysmorphic with nuclear pyknosis, fragmentation, and cytoplasmic vacuolation in >50% of observed cells, the cell membrane was intact, and lymphocytes showed nuclear pyknosis in >50% of the observed cells with nuclear fragmentation in <50% cells. At a PMI between 48 and 72 hours, the neutrophils were no longer identifiable on the smears examined; the eosinophils were no longer identifiable, the monocytes started showing breakdown of the cell membrane but were still identifiable, and lymphocytes showed gross nuclear abnormalities in the form of pyknosis and fragmentation in >50% of cells observed. At a PMI between 72 and 96 hours, the neutrophils and eosinophils were no longer identifiable, the monocytes were no longer identifiable, the lymphocytes were grossly dysmorphic with nuclear pyknosis, fragmentation, and cytoplasmic vacuolation seen in >50% of the observed cells, and the cell membrane was intact. At a PMI between 96 and 120 hours, the neutrophils, eosinophils, and monocytes were no longer identifiable, and lymphocytes showed breakdown of the cell membrane but were still identifiable. Beyond 120 hours, lymphocytes could no longer be identified on smears.”
– There is also no happy ending for most of your thriving necrobiome. For most of these bacteria, the outside’s oxygen is toxic. By dissolving your body, they are working towards their own end without knowing it.
Most gut microbes are so-called “obligate anaerobes”, meaning they die when exposed to oxygen. In a healthy/alive gut, the oxygen levels are extremely low.
#Lee S, Wischmeyer PE, Mintz CD, Serbanescu MA. Recent Insights into the Evolving Role of the Gut Microbiome in Critical Care. Crit Care Clin. 2025
https://pmc.ncbi.nlm.nih.gov/articles/PMC12497176/
Quote: “In states of health, the human gut microbiome (HGM) is comprised of roughly 100 trillion bacteria that occupy the gastrointestinal (GI) tract. Of these, over 99% are obligate anaerobes and require specific growth conditions provided by the intestinal microenvironment.5 As a result, only a fraction of gut microbes (estimated 20%–30%) can be grown using routinely used in clinical microbiology laboratories.6”
Later during putrefaction (the degradation of the dead body by microbes), external microbes enter through the orifices and also become part of the necrobiome. Many of them tolerate oxygen much better than the former gut microbes.
#M. E. Benbow, P. S. Barton, M. D. Ulyshen, J. C. Beasley, T. L. DeVault, M. S. Strickland, J. K. Tomberlin, H. R. Jordan, and J. L. Pechal. 2019. Necrobiome framework for bridging decomposition ecology of autotrophically and heterotrophically derived organic matter. Ecological Monographs89(1):e01331.
Quote: “
The necrobiome is the community of organisms associated with necromass decomposition and includes their interactions with the necromass, with each other, and with their surrounding habitat and ecosystem. This concept is general across plant, fungi, dung/frass/feces, or animal necromass types, and in both terrestrial and aquatic realms. (a) Various qualities of necromass have strong controlling effects on its associated necrobiome. (b) The decomposing necromass is host to a microbiome while alive, both internal (endonecrotic) and external (epinecrotic), and these communities begin to change after death and during the course of decomposition. The changing microbiomes use the organic matter as habitat and for energy and nutrients. As decay progresses, the organic matter and associated activities of the microbes facilitate the attraction of invertebrate and vertebrate saprophages that directly consume the necromass and the microbial communities. (c) All of these biotic components of the necrobiome interact in ways that give rise to pathways of microbial and elemental dispersal away from the decaying necromass into adjacent soil or water media, as well as to the surrounding ecosystem at both localized and broad spatial scales. (d) The necrobiome and its functions operate within a complex network of interactions that are constrained by its terrestrial or aquatic context, the regional species pool, and gradients of abiotic factors. Critically, all these aspects of the necrobiome are interlinked, and the relative importance of each component of the necrobiome, and their function, will depend on the intrinsic qualities of decaying necromass and the extrinsic controlling environmental factors (e.g., temperature, moisture, latitude).”
– Your red blood cells have shriveled up like sickly purple raisins, but the most sturdy ones survive up to a day or two.
#None, D. H. S. G., None, D. S. M., None, D. I. T., None, D. R. J., None, D. S. N., None, D. N. K. & None, D. G. D. K. (2026). Blood Cellular Changes Adjunct in Estimation of Time Since Death. International Journal of Medical and Pharmaceutical Research, 7(1), 2777-2785.
https://ijmpr.in/article/blood-cellular-changes-adjunct-in-estimation-of-time-since-death-2239/
Quote: “Results: Progressive morphological alterations in RBCs were observed with increasing postmortem interval. RBC integrity remained preserved in all cases up to 12 hours and in the majority of cases up to 24 hours. Partial lysis became evident between 24–36 hours, with complete lysis observed beyond 36 hours. Morphological evaluation demonstrated a sequential transition from normal biconcave cells in the earliest interval to slight dysmorphism within 6–12 hours, followed by gross dysmorphism between 12–24 hours. Advanced degeneration and lysis predominated after 24 hours. Central pallor progressively diminished with increasing TSD, with intact pallor observed in early intervals and complete loss beyond 36 hours. Peripheral RBC appearance also demonstrated a transition from hemoglobinized margins to pale outlines and eventual loss of recognizable cellular structures. These findings indicate a consistent and time-dependent pattern of postmortem RBC degeneration.”
#None, D. H. S. G., None, D. S. M., None, D. I. T., None, D. R. J., None, D. S. N., None, D. N. K. & None, D. G. D. K. (2026). Blood Cellular Changes Adjunct in Estimation of Time Since Death. International Journal of Medical and Pharmaceutical Research, 7(1), 2777-2785.
https://pmc.ncbi.nlm.nih.gov/articles/PMC12375393/
Quote: “Postmortem lividity, also known as livor mortis, typically develops within 30 minutes to two hours after death and becomes fixed within eight to 12 hours [1]. The typical purplish hue arises from the accumulation of deoxygenated hemoglobin in dependent blood vessels [2]. However, the color of lividity can vary significantly depending on physiological and environmental factors. In certain contexts, it may appear bright red or cherry-red.”
– In the outer suburbs, your skin and some connective tissues never needed much energy in the first place.
How quickly the skin and other organs succumb to decay processes such as autolysis, necrosis etc. depends very much on the temperature the body is stored at. But generally, the skin and connective tissues such as cartilage are relatively slow at degrading. The reasons for this are manifold, but among the most important factors are the fact that many of those cells are relatively isolated and contained in harder structures (e.g. cartilage), they have low levels of digestive enzymes, they are used to having less oxygen than other tissues, and they may also have a relatively low “cost of living”, i.e their energy requirements for survival are low compared to other tissues. Much of the long-term survival data comes from non-human mammals, which we extrapolate from here.
Generally, the “death and decay timeline” of all organs and tissues strongly depends on the temperature, humidity and other factors, so there is no single, universally correct timeline.
#The Autopsy Book – Autolysis/Postmortem Histology. Retrieved April 2026.
https://theautopsybook.com/autolysis/
Quote: “Type of tissue: Tissues that have cells with a high content of hydrolytic enzymes (pancreas, liver, kidney, digestive tract) undergo autolysis more rapidly. Other tissues that undergo rapid autolysis are: the mucosa of the gallbladder, the adrenal medulla, the neurons of the nervous tissue and the proximal convoluted tubules of the renal cortex. In those tissues constituted by cells with low enzymatic contents (connective tissue, muscle, bone, etc.), autolysis will occur more slowly.”
#Wenzlow N, Neal D, Stern AW, Prakoso D, Liu JJ, Delcambre GH, Beachboard S, Long MT. Feasibility of using tissue autolysis to estimate the postmortem interval in horses. J Vet Diagn Invest. 2021
https://journals.sagepub.com/doi/10.1177/10406387211021865
Quote: “Different cell types undergo postmortem autolysis at different rates because certain cells are more resistant to hypoxia than others.1–3,5,8 The intestinal mucosa, gall bladder, pancreatic parenchyma, and adrenal medulla autolyze first, then neurons are the next most susceptible, with connective tissue the slowest to undergo degradation.1–3,5,8,10 Given that much of this activity is enzymatically driven, the rate of autolysis as well as its evolution to bacterial putrefaction, is slowed by refrigeration.”
#Cetin S, Ataseven T, Kalkanli I, Eren B. Decoding Time of Death: Histopathological Dynamics of Intervertebral Discs as a Novel Marker for Postmortem Interval Estimation. Diagnostics. 2025; 15(5):605.
https://www.mdpi.com/2075-4418/15/5/605
Quote: “The selection of tissues for PMI evaluation is primarily based on factors such as their anatomical position, relationship with surrounding tissues, and postmortem durability [18]. In this regard, cartilage tissue has certain advantages due to its unique structural properties. Being an isolated compartment that lacks nerves, blood vessels, and lymphatics, cartilage tissue is more resistant to postmortem bacterial spread within its extracellular matrix [6]. Its relatively hard structure makes it less susceptible to postmortem decay, further enhancing its suitability for PMI estimation [17]. These features make cartilage tissue particularly valuable for microscopic analysis of histological changes that occur after death.”
#Bardale, Rajesh V. MD; Tumram, Nilesh K. MD; Dixit, Pradeep G. MD(Path), MD(FM); Deshmukh, Ashutosh Y. MD. Evaluation of Histologic Changes of the Skin in Postmortem Period. The American Journal of Forensic Medicine and Pathology 33(4):p 357-361, December 2012.
Quote: “Determination of the time of death is an important consideration in forensic practice. Many methods have been attempted to accurately and systematically determine the postmortem interval (PMI). Histologic examination of the skin or appendages is one of the methods tried by few researchers. However, no attempt had been made to analyze the histologic changes in the skin and appendages simultaneously and to compare them with PMI. We sequentially studied the histologic changes of the skin and appendages in the early PMI. The results of the present study show that the skin undergoes progressive morphological changes in the postmortem period. The epidermis and the dermis appeared normal for 6 hours after death, and after this period, degenerative changes began. By 6 to 9 hours after death, degeneration began in the dermis, and by the end of 18 hours, the dermis began to disintegrate. The sweat glands appeared normal for approximately 3 to 4 hours. For 18 hours after death, the sebaceous glands and hair follicles appeared normal, and after this period, degeneration began.”
#Mauriello S, Treglia M, Pallocci M, Bonfiglio R, Giacobbi E, Passalacqua P, Cammarano A, D’Ovidio C, Marsella LT, Scimeca M. Antigenicity Preservation Is Related to Tissue Characteristics and the Post-Mortem Interval: Immunohistochemical Study and Literature Review. Healthcare. 2022
https://www.mdpi.com/2227-9032/10/8/1495
Quote: “The main aim of this study was to investigate the post-mortem proteolytic degradation process of selected tissue antigens and correlate it to the post-mortem interval. During the autopsy of 12 cadavers (time interval ranging 1 day–2 years after death) samples of skin, liver, kidney, and spleen were collected. All samples were formalin-fixed and paraffin-embedded. Four µm paraffin sections were used for hematoxylin–eosin staining and immunohistochemical analysis (Ki67, Vimentin, Pan cytokeratin, and CD20). Data reported here show that immunohistochemical reactivity preservation was related to the characteristics of the tissues. In particular, the most resistant tissue was the skin, where the autolysis phenomena were not appreciable before 5 days. On the contrary, the liver and the spleen underwent early autolysis, while the kidney displayed an early autolysis of the tubules and a late one of the glomeruli. As concerns specific antigens, immunoreactivity was lost earliest for nuclear antigens as compared to cytoplasmic ones. In conclusion, our results demonstrate that immunohistochemical detection of specific antigens may be useful in estimating the post-mortem interval, especially when we need to know whether the post-mortem interval is a few days or more than 7–10 days.”
#Pitt McGowan Institute for Regenerative Medicine. Human Postmortem Life. Retrieved May 2026
https://humanpostmortemlife.pitt.edu/studying-skin/
Quote: “Many genes are induced in organs, and McGowan will focus on the skin, the largest organ of the body, for its post-mortem conatus research. Skin can live at a cellular level long after death and is a low energy consuming tissue that can harbor living cells longer than other parts of the body. Recent research demonstrates that skin cells could proliferate for 15 days when stored at room temperature (25˚C) or 49 days when refrigerated (4˚C). Skin also possesses cell plasticity—influencing tissue repair and cell survival. Our previous work has shown that the skin can undergo direct in vivo reprogramming, such as when we induced fetal developmental pathways in the skin to achieve vasculogenic reprogramming.”
#Abouhashem AS, Singh K, Srivastava R, Liu S, Mathew-Steiner SS, Gu X, Kacar S, Hagar A, Sandusky GE, Roy S, Wan J, Sen CK. The Prolonged Terminal Phase of Human Life Induces Survival Response in the Skin Transcriptome. bioRxiv [Preprint]. 2023
https://pmc.ncbi.nlm.nih.gov/articles/PMC10245562/
(Note: this is a preprint, it has not yet undergone peer review by a journal)
Quote: “Human death marks the end of organismal life under conditions such that the components of the human body continue to be alive. Such postmortem cellular survival depends on the nature (Hardy scale of slow-fast death) of human death. Slow and expected death typically results from terminal illnesses and includes a prolonged terminal phase of life. As such organismal death process unfolds, do cells of the human body adapt for postmortem cellular survival? Organs with low energy cost-of-living, such as the skin, are better suited for postmortem cellular survival. In this work, the effect of different durations of terminal phase of human life on postmortem changes in cellular gene expression was investigated using RNA sequencing data of 701 human skin samples from the Genotype-Tissue Expression (GTEx) database.
[...] Contrary to other bodily organs such as the brain and heart, the skin tissue maintains its integrity for several hours after death10. No obvious histological changes were identified in either epidermal or human dermal skin layer in the first 18h post-mortem10.”
#Straseski JA, Gibson AL, Thomas-Virnig CL, Allen-Hoffmann BL. Oxygen deprivation inhibits basal keratinocyte proliferation in a model of human skin and induces regio-specific changes in the distribution of epidermal adherens junction proteins, aquaporin-3, and glycogen. Wound Repair Regen. 2009
https://pmc.ncbi.nlm.nih.gov/articles/PMC2743024/
Quote: “The response of normal human stratified squamous epithelium to oxygen deprivation and the molecular and morphological pattern of recovery from this stress are largely unknown. While skin is considered mildly-to-moderately hypoxic under steady-state conditions,1–5 impairment of regional blood vessels by disease or wounding exacerbates the hypoxic status of this organ. It is well established that chronic levels of hypoxia, caused by obstructed blood flow over long periods of time, hamper proper tissue regeneration and promote infection.6,7 The ability of human skin to resist damage following oxygen depletion and/or reoxygenation is clinically relevant to both acute and chronic wounds.”
#Singh, Mahipal & Degala, Venkata. (2017). Postmortem recovery of proliferative fibroblasts up to three days in livestock ear skin stored at 35°C. International Journal of Biology.
https://www.ccsenet.org/journal/index.php/ijb/article/view/64104
Quote: “Effect of elevated temperature (35°C) on postmortem survival of cells in goat, sheep and bovine tissues was studied. Skin explants (n = 30; 2-3 mm2) were cultured in petri dishes after 2, 24, 48, 72, 96 and 120 hours of postmortem interval in DMEM media supplemented with 10% FBS, 50 units/mL of penicillin, 50 µg/mL of streptomycin and 2.5 µg/mL of fungizone. Outgrowth of cells around the explants was observed up to 72 h in sheep, 48 h in bovine and 24 h in goats. In general, the number of explants exhibiting outgrowth as well as the level of confluence decreased with increasing postmortem time interval. Secondary cultures established from primary cells for 72 h postmortem interval show cytogenetically stable chromosomes with 54XX[17] normal female sheep karyotype, comparable cell morphology, and growth curve to that of fresh tissue derived cells. Till date these cells have been passaged 21 times and show normal growth. These results suggest that normal, proliferative cells can be recovered from skin tissues stored at an elevated temperature of 35°C in livestock from 24-72 h of postmortem interval. Reprogramming of these cells to clone the dead animals or their use for cell therapies remain to be seen in future.”
#Walcott, B., & Singh, M. (2017). Recovery of proliferative cells up to 15- and 49-day postmortem from bovine skin stored at 25°C and 4°C, respectively. Cogent Biology.
https://www.tandfonline.com/doi/full/10.1080/23312025.2017.1333760
Quote: “The objective of this study was to assess the time limits within which proliferative cells can be recovered in bovine skin stored separately at 4 and 25°C after animal death. In the first experiment, skin explants (n = 110; 2–3 mm2) from 11 animals stored at 4°C were cultured weekly up to 7 weeks in Dulbecco’s modified Eagle medium (DMEM) supplemented with 10% fetal bovine serum (FBS), 50 units/mL of penicillin, 50 μg/mL of streptomycin, and 2.5 μg/mL of fungizone. The presence/absence of fibroblast-like cell outgrowth around explants was scored. Out of 640 explants cultured, 567 (87%) adhered to dish surface, of which 333 (58.73%) exhibited outgrowth including 16.67% explants from 49 days postmortem tissues. Similarly, in the second experiment, when the tissues were stored at 25 ± 2°C prior to culturing on alternate days up to 17 days, 204 (48%) explants exhibited outgrowth that included 19.15% from 15 dpm tissues. The number of explants exhibiting outgrowth was inversely proportional to postmortem time interval in both temperatures studied. Secondary cultures established from outgrowth for selected time points showed stable chromosomes, normal GFP gene expression, and comparable growth morphology to fresh tissue-derived cells. The cells lasted in culture for more than 20 passages. These results suggest that live and usable cells can be recovered from bovine skin tissues up to about 2 weeks postmortem, if skin is stored at 25°C, and about three times more (>6 weeks), if stored at 4°C.”
– Your genes were built over billions of years of evolution to keep you alive – and the news of your death has not reached all of them yet. Many cells are still translating your DNA into the building blocks of your past life. Long after your death, gene activity in your blood and organs rises and falls in coordinated patterns – frantically trying to activate stress responses and repair you. Some of those genes will remain active for days.
Gene activity patterns postmortem can be difficult to interpret, as some differential expression signatures (especially those observed long after death) may simply reflect greater RNA stability rather than genuine transcriptional activation. However, during the early postmortem period many cells remain alive and metabolically active, making it highly plausible that these mRNA signatures represent true upregulation rather than merely increased transcript stability. In mice and zebrafish, differential expression of genes has been observed >48 h postmortem – this is what we used to support the “active for days” statement.
Humans:
#Antiga, L.G., Sibbens, L., Abakkouy, Y. et al. Cell survival and DNA damage repair are promoted in the human blood thanatotranscriptome shortly after death. Sci Rep 11, 16585 (2021).
https://www.nature.com/articles/s41598-021-96095-z
Quote: “RNA analysis of post-mortem tissues, or thanatotranscriptomics, has become a topic of interest in forensic science due to the essential information it can provide in forensic investigations. Several studies have previously investigated the effect of death on gene transcription, but it has never been conducted with samples of the same individual. For the first time, a longitudinal mRNA expression analysis study was performed with post-mortem human blood samples from individuals with a known time of death. The results reveal that, after death, two clearly differentiated groups of up- and down-regulated genes can be detected. Pathway analysis suggests active processes that promote cell survival and DNA damage repair, rather than passive degradation, are the source of early post-mortem changes of gene expression in blood. In addition, a generalized linear model with an elastic net restriction predicted post-mortem interval with a root mean square error of 4.75 h. In conclusion, we demonstrate that post-mortem gene expression data can be used as biomarkers to estimate the post-mortem interval though further validation using independent sample sets is required before use in forensic casework.”
#Ferreira, P.G., Muñoz-Aguirre, M., Reverter, F. et al. The effects of death and post-mortem cold ischemia on human tissue transcriptomes. Nat Commun 9, 490 (2018).
https://www.nature.com/articles/s41467-017-02772-x
Quote: “Post-mortem tissues samples are a key resource for investigating patterns of gene expression. However, the processes triggered by death and the post-mortem interval (PMI) can significantly alter physiologically normal RNA levels. We investigate the impact of PMI on gene expression using data from multiple tissues of post-mortem donors obtained from the GTEx project. We find that many genes change expression over relatively short PMIs in a tissue-specific manner, but this potentially confounding effect in a biological analysis can be minimized by taking into account appropriate covariates. By comparing ante- and post-mortem blood samples, we identify the cascade of transcriptional events triggered by death of the organism. These events do not appear to simply reflect stochastic variation resulting from mRNA degradation, but active and ongoing regulation of transcription. Finally, we develop a model to predict the time since death from the analysis of the transcriptome of a few readily accessible tissues.”
#Zhu, Y., Wang, L., Yin, Y. et al. Systematic analysis of gene expression patterns associated with postmortem interval in human tissues. Sci Rep 7, 5435 (2017).
https://www.nature.com/articles/s41598-017-05882-0
Quote: “Postmortem mRNA degradation is considered to be the major concern in gene expression research utilizing human postmortem tissues. A key factor in this process is the postmortem interval (PMI), which is defined as the interval between death and sample collection. However, global patterns of postmortem mRNA degradation at individual gene levels across diverse human tissues remain largely unknown. In this study, we performed a systematic analysis of alteration of gene expression associated with PMI in human tissues. From the Genotype-Tissue Expression (GTEx) database, we evaluated gene expression levels of 2,016 high-quality postmortem samples from 316 donors of European descent, with PMI ranging from 1 to 27 hours. We found that PMI-related mRNA degradation is tissue-specific, gene-specific, and even genotype-dependent, thus drawing a more comprehensive picture of PMI-associated gene expression across diverse human tissues. Additionally, we also identified 266 differentially variable (DV) genes, such as DEFB4B and IFNG, whose expression is significantly dispersed between short PMI (S-PMI) and long PMI (L-PMI) groups. In summary, our analyses provide a comprehensive profile of PMI-associated gene expression, which will help interpret gene expression patterns in the evaluation of postmortem tissues.”
#Dachet, F., Brown, J.B., Valyi-Nagy, T. et al. Selective time-dependent changes in activity and cell-specific gene expression in human postmortem brain. Sci Rep 11, 6078 (2021).
https://www.nature.com/articles/s41598-021-85801-6
Quote: “As a means to understand human neuropsychiatric disorders from human brain samples, we compared the transcription patterns and histological features of postmortem brain to fresh human neocortex isolated immediately following surgical removal. Compared to a number of neuropsychiatric disease-associated postmortem transcriptomes, the fresh human brain transcriptome had an entirely unique transcriptional pattern. To understand this difference, we measured genome-wide transcription as a function of time after fresh tissue removal to mimic the postmortem interval. Within a few hours, a selective reduction in the number of neuronal activity-dependent transcripts occurred with relative preservation of housekeeping genes commonly used as a reference for RNA normalization. Gene clustering indicated a rapid reduction in neuronal gene expression with a reciprocal time-dependent increase in astroglial and microglial gene expression that continued to increase for at least 24 h after tissue resection. Predicted transcriptional changes were confirmed histologically on the same tissue demonstrating that while neurons were degenerating, glial cells underwent an outgrowth of their processes. The rapid loss of neuronal genes and reciprocal expression of glial genes highlights highly dynamic transcriptional and cellular changes that occur during the postmortem interval. Understanding these time-dependent changes in gene expression in post mortem brain samples is critical for the interpretation of research studies on human brain disorders.”
Non-human animals:
#Bonadio, R.S., Nunes, L.B., Moretti, P.N.S. et al. Insights into how environment shapes post-mortem RNA transcription in mouse brain. Sci Rep 11, 13008 (2021).
https://www.nature.com/articles/s41598-021-92268-y
Quote: “Most biological features that occur on the body after death were already deciphered by traditional medicine. However, the molecular mechanisms triggered in the cellular microenvironment are not fully comprehended yet. Previous studies reported gene expression alterations in the post-mortem condition, but little is known about how the environment could influence RNA degradation and transcriptional regulation. In this work, we analysed the transcriptome of mouse brain after death under three concealment simulations (air exposed, buried, and submerged). Our analyses identified 2,103 genes differentially expressed in all tested groups 48 h after death. Moreover, we identified 111 commonly upregulated and 497 commonly downregulated genes in mice from the concealment simulations. The gene functions shared by the individuals from the tested environments were associated with RNA homeostasis, inflammation, developmental processes, cell communication, cell proliferation, and lipid metabolism. Regarding the altered biological processes, we identified that the macroautophagy process was enriched in the upregulated genes and lipid metabolism was enriched in the downregulated genes. On the other hand, we also described a list of biomarkers associated with the submerged and buried groups, indicating that these environments can influence the post-mortem RNA abundance in its particular way.”
#Olney KC, Gibson KA, Cadiz MP, Rahimzadeh N, Swarup V, Fryer JD. Postmortem Interval Leads to Loss of Disease-Specific Signatures in Brain Tissue. eNeuro. 2025
https://www.eneuro.org/content/12/3/ENEURO.0505-24.2025
Quote: “Human brain banks are essential for studying a wide variety of neurological and neurodegenerative diseases, yet the variability in postmortem interval (PMI)—the time from death to tissue preservation—poses significant challenges due to rapid cellular decomposition, protein alterations, and RNA degradation. Furthermore, the postmortem transcriptomic alterations occurring within distinct cell types are poorly understood. In this study, we analyzed the effect of a 3 h postmortem interval on single-nucleus RNA signatures in the brains of wild-type (WT) and PS19 mice, a common model of tauopathy. We observed that basic quality control metrics (such as the number of genes and reads per cell), total nuclei counts, and RNA integrity number (RINe) remained consistent across all samples, regardless of PMI or genotype. However, a 3 h PMI diminished the number of genes differentially expressed between PS19 and WT mice, suggesting an impact of delayed processing on the detection of disease-specific transcriptomic signatures. When directly comparing 3 h PMI versus freshly harvested 0 h mouse brains, we identified genes upregulated in neurons and interneurons involved in DNA repair, immune response, and stress pathways. Furthermore, genes that were altered in non-neuronal cell types at 3 versus 0 h PMI were associated with cell–cell adhesion processes. These findings highlight the effects of PMI on single-nucleus transcriptional changes that may dampen the true changes in cellular states in banked brain tissues.”
#Alex E. Pozhitkov, Rafik Neme, Tomislav Domazet-Lošo, Brian G. Leroux, Shivani Soni, Diethard Tautz, Peter A. Noble; Tracing the dynamics of gene transcripts after organismal death. Open Biol 1 January 2017
Quote: “In life, genetic and epigenetic networks precisely coordinate the expression of genes—but in death, it is not known if gene expression diminishes gradually or abruptly stops or if specific genes and pathways are involved. We studied this by identifying mRNA transcripts that apparently increase in relative abundance after death, assessing their functions, and comparing their abundance profiles through postmortem time in two species, mouse and zebrafish. We found mRNA transcript profiles of 1063 genes became significantly more abundant after death of healthy adult animals in a time series spanning up to 96 h postmortem. Ordination plots revealed non-random patterns in the profiles by time. While most of these transcript levels increased within 0.5 h postmortem, some increased only at 24 and 48 h postmortem. Functional characterization of the most abundant transcripts revealed the following categories: stress, immunity, inflammation, apoptosis, transport, development, epigenetic regulation and cancer. The data suggest a step-wise shutdown occurs in organismal death that is manifested by the apparent increase of certain transcripts with various abundance maxima and durations.”
– And finally, deep within your muscles and bone marrow, stem cells trigger a survival program, slowing down their metabolism and entering a sort of deep sleep – just for the tiniest chance that there will be a time to rebuild your body. It will take weeks for the last of these survivors of a fallen planet to die.
In our scenario, we don't specify how your body/cadaver will be stored after the first few hours have passed. Maybe someone found the body and it was transported to a morgue. There, it will be cooled for storage until further processing. If you are not cremated or buried immediately, it is possible that some stem cells deeply embedded in your body will survive for several weeks.
There is a lack of data on stem cell viability in cadavers stored at room temperature. But in cadavers stored refrigerated, we know that stem cells can survive for over 2 weeks.
Human stem cells viable 17 days post-mortem (cooled cadaver):
#Latil, M., Rocheteau, P., Châtre, L. et al. Skeletal muscle stem cells adopt a dormant cell state post mortem and retain regenerative capacity. Nat Commun 3, 903 (2012).
https://www.nature.com/articles/ncomms1890
Quote: “The accessibility to stem cells from healthy or diseased individuals, and the maintenance of their potency are challenging issues for stem cell biology. Here we report the isolation of viable and functional skeletal myogenic cells from humans up to 17 days, and mice up to 14 days post mortem, much longer beyond previous reports. Muscle stem cells are enriched in post mortem tissue, suggesting a selective survival advantage compared with other cell types. Transplantation of mouse muscle and haematopoietic stem cells regenerates tissues robustly. Cellular quiescence contributes to this cell viability where cells adopt a reversible dormant state characterized by reduced metabolic activity, a prolonged lag phase before the first cell division, elevated levels of reactive oxygen species and a transcriptional status less primed for commitment. Finally, severe hypoxia, or anoxia is critical for maintaining stem cell viability and regenerative capacity. Thus, these cells provide a useful resource for studying stem cell biology.”
Human stem cells viable 7 days postmortem (cooled cadaver):
#Saito T, Sato T, Suzuki K. Isolation and culture of human adipose-derived mesenchymal stromal/stem cells harvested from postmortem adipose tissues. J Forensic Leg Med. 2020
https://www.sciencedirect.com/science/article/pii/S1752928X19301118?via%3Dihub
Quote: “Many cell types maintain their function short-term after death. Stem cells isolated from postmortem tissues have been successfully applied in transplantation studies. However, stem cell viability and stemness are reported to decline with increased time after death. Although postmortem stem cells may be useful for regenerative therapy and forensic diagnostics, their characteristic remain to be better understood. Adipose-derived mesenchymal stromal/stem cells (ASCs) have the capacity to differentiate through several cell lineages and are able to survive in an ischemic environment for a prolonged time. This study aimed to confirm whether human postmortem ASCs can be collected and culture-expanded from cadavers. Axilla subcutaneous adipose tissues were harvested during forensic autopsy and enzymatically digested to obtain a heterogeneous cell mixture, including the ASCs population. The mixture was seeded onto collagen-coated cell culture dishes and spindle-shaped adhesive and proliferative ASCs were confirmed. Senescent cells were also present, visualized as large and flattened cells. When maintained in a cool environment, ASCs were able to survive in the postmortem tissues for up to 7 days after death. We conclude that postmortem ASCs can be readily isolated and culture-expanded from adipose tissues.”
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