biology gcse

• 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.
• If the levels of ions or water get too high or too low it can start to damage our cells and cause problems.
• Sweat is a natural way to regulate ions, but the main way we regulate ions is through our kidneys.
• 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.
• Most of the water has to be lost from the kidneys in the form of urine.
• The kidneys remove waste products like urea and regulate substances like ions and water.
• Each of our two kidneys contain around a million structures called nephrons which perform the filtration and selective reabsorption process.
• Inside the brain, there's a structure called the hypothalamus which detects the concentration of water in the bloodstream and sends a signal to the pituitary gland if the water levels in the body are too low.
• The pituitary gland releases a hormone called adh or antidiuretic hormone into the bloodstream which reaches the kidneys and tells the tubules to reabsorb more water into the blood, increasing the amount of water in the bloodstream and producing less urine.
• If the water levels in the body get too high, the hypothalamus will stop sending signals to the pituitary gland and the pituitary gland will release less adh, causing the kidneys to reabsorb less water into the blood and produce more urine.
• This process of water regulation is an example of a negative feedback loop as the body constantly monitors our water levels and adjusts 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 known as 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 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 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, which can quickly make the person sick and even lead to death.
• 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 can filter a patient's blood for them, even if their kidneys don'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.
• Dialysis is an unpleasant experience that can cause problems like blood clots or infections.
• 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 blood to lose all the junk it doesn't want, such as any extra ions or amino acids, and pretty much all of the urea.
• Doctors help patients by giving them medication to suppress their immune system, but unfortunately, it doesn't always work.
• Even though transplants tend to be better and much cheaper than dialysis, there's not enough available organs to give everybody a transplant, so many people still have to rely on dialysis.
• An alternative to dialysis is a kidney transplant, 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.