The Kidneys

• The main job of the kidneys is to filter the blood and remove all 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 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 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 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.
• 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 known as a nephron.
• The yellow part of a nephron is the tubule which carries the filtered fluid that becomes urine.
• 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 red parts of a nephron are the blood vessels.
• 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.
• Filtration is the process that starts up in the kidneys, where some of the liquid part of the blood is forced from the glomerulus into the bowman's capsule, the start of the tubule.
• 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, for example, glucose and amino acids are reabsorbed almost entirely, while water and ions are reabsorbed selectively, and urea is not reabsorbed.
• The process of reabsorbing these substances 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.
• The dialysis fluid is constantly replaced with new fluid being pumped in from the bottom and older fluid passing out of the top, creating a concentration gradient that causes the loss of all unwanted substances in the blood.
• As the patient's blood passes through the machine, it loses all the junk it doesn't want like any extra ions or amino acids, and pretty much all of the urea.
• Once the blood has been passed through the machine, it is much cleaner and can go back into the patient.
• 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.
• Dialysis is an unpleasant experience that can cause problems like blood clots or infections.
• Dialysis is a very expensive treatment that patients will need to have continually for the rest of their life.
• A kidney transplant is an alternative to dialysis, a surgical procedure where a healthy kidney from one person is transferred to a patient that needs it.
• Most of the donor kidneys for transplants come from people who have recently died, but living people can also donate to kidney as we're all born with two of them.