Medicine

What is stress?

By Divya Ganesh, Ananya Rastogi, Shreya Mokkapati

An article by Dr Gillian Butler explains that there are three ways in which we can define stress.

First, a stimulus-based definition. This explains that stress is a threatening event or situation, like a job interview or a test. The definition characterises stress as a stimulus which can cause a reaction. This can become a problem because it seems subjective - different people consider different situations as threatening.

Secondly, a response based definition. This focuses on physiological responses to a threatening situation: but some of these physiological responses (like an accelerated heart rate) can also happen as a response to things people wouldn’t consider stressful, for example when you receive unexpected good news.

The definition with the most value is viewing stress as a dynamic process where someone perceives and responds to threatening events. The important part of this definition is where it includes how we each judge threats - taking into account different people’s perceptions of the same event. [1]

Types of stress

Stress is your body’s response to certain situations. It’s subjective, so something that is stressful for you may not be stressful for someone else. There are many different kinds of stress and not all of them are bad. In fact, some stress heightens your senses, helping you to avoid accidents, reach unexpected deadlines, or stay clear-minded in chaotic situations. This is the fight-or-flight response that the body triggers in times of pressure. But stress is meant to be temporary. Your body should return to a natural state after the situation has passed.

However, there are different types of stress, some of which aren’t as temporary as they should be.

Acute stress is the most common type of stress. It’s your body’s immediate reaction to a new challenge, event, or demand, and it triggers your fight-or-flight response: for example when you are on a rollercoaster, or if there is a jumpscare in a horror movie. Therefore, acute stress isn’t too negative on the body - in fact, it gives your body and brain practice in developing the best response to future stressful situations.

When acute stress happens frequently, it’s called episodic acute stress. People who suffer from this are often short-tempered, irritable, and anxious. Negative health effects are also persistent in people with episodic acute stress.

If acute stress isn't resolved and begins to increase or lasts for long periods of time, it becomes chronic stress. This stress is constant and doesn’t go away. It can contribute to several serious diseases including heart disease, cirrhosis, cancer and lung disease. [2]

Definitions

Amygdala= area of brain primarily associated with emotional processes, thought to be part of the limbic system

Limbic system= emotions, memory, survival instinct

Sympathetic nervous system= à division of the autonomic nervous system, involved in stimulating the fight-or-flight response

Autonomic nervous system= regulating involuntary actions (controlling internal organs and glands)

HPA axis= hypothalamic-pituitary-adrenal axis

Adrenal glands= endocrine glands that secrete catecholamines, located above the kidneys

Understanding the stress response

There are 4 steps in the stress response. General overview of the process: 1. Amygdala sends a distress signal to the hypothalamus, which is in charge of the stress response.

The hypothalamus controls two processes - what’s labelled as number 2, the short term response (fight-or-flight) and number 3, the longer term stress response.

In more detail: in the sympathomedullary pathway the hypothalamus stimulates the adrenal medulla (part of the sympathetic nervous system) to secrete adrenaline and noradrenaline. We’ll talk about the effects of these hormones later on.

Then in the HPA axis: hypothalamus releases corticotropin-releasing hormone which stimulates the pituitary gland to release adrenocorticotropic hormone. Next, the adrenal glands release cortisol. [3]

The negative feedback mechanism is a control loop. High cortisol levels are detected by receptors in the hypothalamus and the hippocampus. This turns off the HPA axis stimulation so it inhibits further cortisol production. Body returns back to a balanced state again - so this stress response is designed to be an on/off event - an evolutionary advantage for humans. [4]

Hormones involved

Different hormones play different roles in the stress response, adding to the physiological and physical effects already on the body. The three main hormones, as aforementioned, include adrenaline, cortisol and norepinephrine.

1. Adrenaline works with norepinephrine (also referred to as noradrenaline), as the ‘fight or flight hormone’ released from the adrenal glands, located above the kidneys in the body. This controls the immediate responses from the body, such as a faster heart rate, tenser muscles and more sweating.

• The adrenaline is released due to emotional signals from the amygdala to the sympathomedullary pathway, which sends a signal to the adrenal glands for hormone secretion through the autonomic nervous system (ANS).
• The adrenaline hormones travel through the blood and bind to liver receptor cells.
• This breaks down large glycogen molecules into glucose to be used by the body cells for respiration
• It also binds to lung muscle, heart muscle and muscles below skin causing the faster heart rate, panting and perspiration.
• Most importantly, it binds to pancreatic receptors, inhibiting the production of insulin - a hormone which turns glucose back into glycogen. [5]

1. Norepinephrine, or noradrenaline, is another hormone released from the adrenal glands that increase arousal and responsiveness. It can often make you feel more awake and aware of your surroundings. The main difference between noradrenaline and adrenaline is that adrenaline attaches to both alpha and beta receptors whilst this attaches to alpha receptors, found only in the arteries.

• Norepinephrine does the same thing as adrenaline and is released in the same way.
• However, norepinephrine is able to make the arteries narrower by contraction, causing blood to be pumped at a higher pressure, increasing oxygen availability for muscle cells, ready for high rates of respiration.
• It also helps to shift blood flow away from areas where it might not be as useful e.g. near the skin, to more essential cells e.g. muscle tissue, through its ability to contract the arteries (limiting blood flow).

Although both adrenaline and norepinephrine elevate these symptoms, the ANS has direct connections to the heart, causing direct heart rate and blood pressure increase from the sympathomedullary pathway response. Since these are stimulated by the ANS, the effect travels very fast, giving the most noticeable physical effects straight away. [6]

1. Cortisol is a steroid hormone, meaning it’s produced from the lipid cholesterol and is also released by the adrenal glands. It’s triggered by the HPA axis instead (hypothalamus, pituitary gland, adrenal gland), meaning it has a slightly longer lag time from the first detection of stress than the other two hormones. Most cells have cortisol receptors so cortisol affects many functions. Some include:

• It binds to the amygdala and hippocampus, the brain’s key regions for learning and memory, helping memory formulation. On the other hand, high cortisol levels can also hinder memory recall, which leads to experiences such as ‘mind blanks’ during stressful situations or exams.
• It also stimulates ADH production causing higher water retention and bloating
• Most importantly, it regulates some body functions that aren't crucial at the moment, like reproductive drive, immunity, digestion and growth.

Oestrogen and testosterone are also hormones that affect how we react to stress, as are the neurotransmitters dopamine and serotonin, but the main reaction is mostly due to these three. Although the same hormones are used, there are different types of stress. [7]

Physiological effects of the stress hormones

Endocrine system

• Some people don’t reabsorb the extra blood sugar that their liver pumps out, and they may be more likely to develop type 2 diabetes.
• Overexposure to cortisol can lead to thyroid problems and affect your ability to think clearly.
• In men, chronic stress can also affect sperm and testosterone production, and cause erectile dysfunction and infections in the testes, prostate, or urethra.
• In women, chronic stress can worsen PMS, cause changes in the menstrual cycle, and missed periods. It can also aggravate symptoms of menopause and decrease sexual desire.

Respiratory system

• Short term: You breathe harder and faster, and can even hyperventilate, which can cause panic attacks in some people.
• Long term: Aggravates asthma or emphysema if pt suffers from these also.

Cardiovascular system

-Long term: Consistently elevated heart rate, blood pressure, and stress hormones can increase your odds of heart attack, stroke, and hypertension. These can also affect cholesterol levels and cause inflammation in your circulatory system. [8]

Health conditions related to stress

1. Sometimes tumors on the pituitary or adrenal glands can contribute to a condition known as Cushing syndrome, which is characterized by high levels of cortisol in the blood. Individuals with Cushing syndrome will experience rapid weight gain in the face, abdomen, and chest. Often doctors will notice this because of the individual's slender arms and legs compared to heavy weight in the core of the body. Cushing syndrome also causes a flushed face, high blood pressure, and changes in the skin. Osteoporosis and mood swings are also a factor considered with Cushing disease. [7]

2. Anxiety and depression may also be linked to high cortisol levels. In 2009 Vreeberg and colleagues reported that in roughly 50% of people with depression, cortisol level peaks earlier in the morning than in people without depression, and does not decrease over the course of the day. [9]