The Kidneys

• Water can leave the human body through the lungs when we exhale, through sweat, and through the kidneys.
• The kidney plays a crucial role in maintaining the concentration of substances in the blood.
• Excess amino acids are dealt with by the liver which produces a chemical called ammonia.
• The liver immediately converts ammonia to urea which can be safely excreted by the kidneys.
• The main job of the kidneys is to filter the blood and remove all of the waste that we don't want, with urea being the main waste product.
• The kidneys also regulate the levels of useful things like ions and water which we need to keep at the right levels.
• We gain ions like sodium and potassium ions from our diet and need them for all sorts of things in the body, but if the levels get too high or too low it can start to damage our cells and cause problems.
• Water regulation is a bit more complex as we lose some water naturally during sweating and lose more from our skin when we sweat and our lungs when we breathe, but most of the water has to be lost from the kidneys in the form of urine.
• The main roles of the kidneys are to remove waste products like urea and regulate other substances like ions and water.
• Each of our two kidneys contain around a million structures called nephrons, which perform the filtration and selective reabsorption of substances.
• Inside the brain, there's a structure called the hypothalamus which detects the concentration of water in the bloodstream, and if it detects that the water levels in the body are too low, it sends a signal to the pituitary gland which sits just in front of the brain behind our eyes.
• The signals from the hypothalamus tell the pituitary gland to release a hormone called adh or antidiuretic hormone into the bloodstream, which as it travels around the body reaches the kidneys and tells the tubules to reabsorb more water into the blood, increasing the amount of water in the bloodstream and reducing the amount of urine produced.
• If the water levels in the body get too high, the hypothalamus will stop sending signals to the pituitary gland and so the pituitary gland won't release as much adh, resulting in less adh reaching the kidneys and them reabsorbing less water into the blood, leading to more water staying in the tubules and the kidneys having to produce more urine to get rid of the extra water.
• The process of water regulation is an example of a negative feedback loop as the body is constantly monitoring our water levels and adjusting them to make them balance.
• The three main roles of the kidneys are to remove waste products like uvea from the blood, regulate the levels of ions in the blood, and regulate the amount of water in the blood.
• Blood constantly cycles through the kidneys, passing in through the renal arteries and out through the renal veins.
• The kidneys produce urine which passes down the ureters and is stored in the bladder until urinated out through the urethra.
• The urine production process is complex and involves understanding the anatomy of the kidneys, specifically the structure of the nephron.
• A kidney can be sliced down the middle in a cross-section, revealing a structure called a nephron.
• The yellow part of a nephron is the tubule which carries the filtered fluid that becomes urine.
• The red parts of a nephron are the blood vessels.
• Filtration is the process that begins in the kidneys, where some of the liquid part of the blood is forced from the glomerulus into the bowman's capsule.
• Only very small substances can be filtered through to the boneless capsule, so only things like water, amino acids, urea, glucose, and ions can pass through.
• The fluid that passes through the tubules in the kidneys reabsorbs all the things it wants back into the blood vessels, such as glucose and amino acids, but only reabsorbs some of the water and ions, and absorbs none of the urea.
• This process of reabsorption is called selective reabsorption and it happens throughout the entire region as a fluid makes its way through the tubule.
• The different parts of the nephron are named as follows: glomerulus, bowman's capsule, proximal convoluted tubule, loop of henle, distal convoluted tubule, and collecting duct.
• Any fluid that passes out of the collecting duct is classified as urine and will pass down the ureter to the bladder and can then be released as waste.
• Kidney failure occurs when the kidneys stop functioning, leading to the build-up of waste substances in the bloodstream and the inability to regulate water and ion levels.
• The main consequences of kidney failure are sickness and potentially death if not treated.
• Mild kidney disease can be treated with medication, but the only treatment for kidney failure is dialysis or kidney transplant.
• Dialysis machines are artificial kidneys that filter a patient's blood for them, even if theirs doesn't work properly.
• In dialysis, the patient's blood passes into the machine through the circuit, then back out into the patient.
• While in the machine, the patient's blood comes into contact with the dialysis fluid, which is a mixture that contains the same concentrations of water and other molecules as healthy blood.
• The dialysis fluid contains a reasonable quantity of glucose ions and amino acids but no urea because healthy blood doesn't have any urea.
• If the patient has too much of anything like too many ions or too much water, they will diffuse across the partially permeable membrane into the dialysis fluid because there will be a concentration gradient, bringing the patient's blood levels back to normal.
• After a while, equilibrium is reached and nothing diffuses anymore, so to prevent this, the dialysis fluid is periodically changed.
• Even though transplants tend to be better and much cheaper than dialysis, there's not enough available organs to give everybody a transplant and so many people still have to rely on dialysis.
• Dialysis is a time-consuming treatment that requires patients to go into hospital three to four days a week and be hooked up to the machine for three to four hours each time.
• A kidney transplant is a risky procedure with the main risk for the patient being organ rejection, when a transplanted organ is attacked by the patient's own immune system which treats it as a foreign object and wants to destroy it.
• Once the blood has been passed through the machine, it is much cleaner and can go back into the patient.