Kidneys

• The main job of the kidneys is to remove waste products such as urea (which is made up of extra amino acids that become fats and carbohydrates). The kidneys also filter the blood.
• The kidneys regulate the levels of ions.
• The kidneys regulate water by losing them in the form of urine.
• Water regulation is so important because if we have too much water in our cells they could swell or burst. If we have too little they could lose their water and shrink.
• In the kidneys there are millions of nephrons. Nephrons contain tubules that absorb water, glucose, amino acids and urea, basically anything small (filtration). The kidneys reabsorb all the things we want to keep. This is selective reabsorption. We reabsorb all glucose, some water and no urea.
• The hypothalamus detects levels of water in the bloodstream. If they are too low a signal is sent to the pituitary gland. The pituitary gland releases ADH which tells the tubules to reabsorb more water. This means we will produce less urine.
• If there is too much water in the bloodstream the hypothalamus will stop sending signals to the pituitary gland. It won't release as much ADH. The tubules will reabsorb less water and produce more urine.
• If we were to perform a cross-section on a kidney we would see millions of nephrons, containing tubules and blood vessels.
• The process starts with filtration. Some of the small substances from the blood are put into the bowman's capsule which is the start of the tubules. Only 20% of the plasma in the blood is filtered through the bowmans capsule.
• The fluid passes along the tubules and the kidneys reabsorb all amino acids and glucose and some of the water and ions. No urea. This is selective reabsorption.
• Any fluid that passes out of the collecting duct is urine.
• The main consequences of kidney failure are a build-up of waste substances in the blood stream and an inability to regulate ion and water levels in the bloodstream
• Kidney failure quickly causes someone to become and sick and can kill
• mild kidney disease can be treated with medication
• kidney failure can be treated by dialysis. They are machines that filter a patient's blood for them. Their blood can pass through the machine and be filtered by a partially permeable membrane and then be passed back into them. If the patient has too much of anything it will diffuse into the dialysis fluid. The fluid is constantly replaced so there is always a concentration gradient.
• The problem with dialysis is that it is very time-consuming. Patients must go to the hospital 3-4 days a week for 3-4 hours each time. It is an unpleasant experience and can cause blood clots and infection. It is also very expensive to run.
• Kidney transplants can be transferred from a healthy person to a patient who needs one. They can be given by a recently dead person or a living person can donate one. The main risk is that the organ will be rejected.
• There are not enough organs for everyone to have a kidney transplant.