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Intro
What is the Excretory System?
The excretory system is the body system responsible for removing waste products from the body. The primary organs involved in this system are the kidneys, bladder, ureters, and urethra.
The Kidneys
The Kidneys
The kidneys control blood pressure by adjusting the fluid volume of the blood
Aldosterone increases Na+ transport, water follows by osmosis
Blood pressure is monitered by the juxtaglomerular apparatus
Low blood pressure causes a release of renin what activates angiotensis which causes the blood vessels to constrict as well signaling for the release of aldosterone to increase fluid reabsoption
The Nephron
What is it? The nephron is a functional unit of a kidney; each kidney contains around 1 million nephrons
Function: To filter blood, remove wastes, and balance water, salts, and other substances in the body
How it works:
Glomerulus: a bundle of capillaries that only allow water, urea, glucose, and salts through to Bowman's capsule, and hold back large molecules like proteins and red blood cells
Bowman's capsule: collects the filtered fluid, called filtrate, which begins the process of urine formation
Proximal Convoluted Tubule: As the filtrate goes through, useful substances like glucose, amino acids, salts, and some water are reabsorbed into the blood
Loop of Henle: As the filtrate enters the descending loop, the membrane is made permeable so water is reabsorbed back into the blood. Then, the filtrate enters the ascending loop, where the membrane is now impermeable to water, so only salts are reabsorbed
Distal Convoluted Tubule: fine-tunes the final urine composition by adjusting and regulating salt levels, pH, and waste balance
Collecting duct: urine passes into the collecting duct, and ADH absorbs more or less water depending on the body's hydration levels
Homeostasis
The excretory system helps maintain a stable internal body environment by controlling the composition, volume, and balance of blood and bodily fluids, as well as filtering out waste from the blood
Water balance: Regulated by ADH, a hormone produced by the hypothalamus, in response to hydration levels in the body: when you are dehydrated, ADH will signal the kidneys to reabsorb more water, and when you are hydrated, it will signal the kidneys to stop absorbing as much water
Salt and ion balance: Regulated by aldosterone (which controls sodium and potassium) and PTH (which controls calcium), which helps muscle/nerve function, hydration levels, and blood pressure
pH balance: The kidneys regulate pH by secreting hydrogen ions and reabsorbing bicarbonate to raise pH (make it more acidic) and vice versa when pH is too low
Removal of waste: The kidneys filter out urea and other nitrogenous wastes to prevent buildup, and buildup could prove fatal if left unmanaged
Blood pressure regulation: When kidneys detect abnormal blood pressure, they release renin, which creates angiotensin I and II, which constrict blood vessels and stimulate the release of aldosterone, which increases blood volume, as well as the release of ADH, which also increases blood pressure and volume
Feedback Loops
Positive: the output of a system keeps increasing until a certain outcome is reached, which amplifies change and goes outside the normal range in one direction until it is over (examples: labour and oxytocin, fruit ripening)
Negative: counteracts a change in a system, maintains the regular/normal range. There are many examples, such as temperature, water balance, and blood sugar levels.
Temperature: for a rise in temperature, it detects and triggers sweating and the widening of blood vessels which cool the body back down. For a lower temperature, the body triggers the contraction of muscles and shivering to warm the body back up.
Water balance: detects dehydration and high salt levels, and releases more ADH so the kidneys reabsorb more water, and once the water levels are back to normal, the production of ADH lowers or stops
Blood sugar: blood sugar will rise after eating, which is detected by the pancreas, which releases insulin to store glucose as glycogen in the liver. The release of insulin decreases as sugar levels go back down. When sugar levels are too low, the pancreas will release glucagon, which converts the stored glycogen back into the active glucose
Example of a Negative Feedback Loop
Example of a Negative Feedback Loop
Shivering to warm up
Sweating to cool down
Example of a Positive Feedback Loop
Example of a Positive Feedback Loop
Contractions cause the release of oxytocin, which makes the contractions stronger and more frequent until the baby is born
Endotherms and Ectotherms
Endotherms: warm-blooded animals that maintain their body temperature internally through metabolism, which remains constant even when their external environment changes; they also require more food (ex. humans, birds, mammals)
Ectotherms: rely on external sources to regulate their body temperature, change with the environment, require less food (ex. reptiles, amphibians, insects, fish)
Endotherm
Endotherm
Ectotherm
Ectotherm
Diseases and Disorders
Diabetes Insipidus: The body doesn’t make or respond to ADH, which means the kidneys don’t reabsorb enough water, so the body loses too much water, which leads to dilute urine, extreme thirst, dehydration risk, and the potential treatment is desmopressin or a transplant
Diabetes Mellitus: The body doesn’t properly make or use insulin, leading to high blood sugar; potential treatments include insulin/medication or a transplant
Bright's disease: Inflammation of the glomeruli, seen by proteins in the urine; potential treatment would be dialysis, antibiotics, steroids, or a transplant
Kidney stones: Hard crystals made up of minerals, salts, and calcium can cause severe pain and infection. Potential treatment would be to drink lots of water, take painkillers, or, in extreme cases, undergo surgery
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