CONTROLLING INTERNAL CONDITIONS
The internal conditions of the body must be carefully controlled. Keeping internal conditions within a narrow range is called homeostasis. Temperature, blood glucose levels, water and ion content and the levels of waste products must all be controlled. Waste products that have to be removed from the body include carbon dioxide and urea. Carbon dioxide is produced in respiration and is removed via the lungs when we breathe out. Urea is produced by the liver and must be removed in the urine. It is produced by the breakdown of amino acids and is temporarily stored in the bladder. Water and ions enter the body when we eat and drink. If the water or ion content in the body is wrong, too much water may move into or out of cells. This could damage or destroy the cells.
THE HUMAN KIDNEY
The body has two kidneys. Their role is to filter the blood and control the excretion of substances you don't need and keeping the substances that the body does need. A healthy kidney produces urine by first filtering the blood flowing through it. All the sugar is then reabsorbed. Some of the mineral ions and water are reabsorbed, depending on how much the body needs. Urea, excess mineral ions and water are then released in the urine. The urine is temporarily stored in the bladder before being removed from the body through urination.
DIALYSIS - AN ARTIFICIAL KIDNEY
If a person suffers from kidney failure, they can be kept alive by dialysis. A dialysis machine carries out the same job as the kidneys. It filters the blood and gets rid of the substances that they body doesn't need. The blood flows between partially permeable membranes. The dialysis fluid contains the same concentration of useful substances as the blood, so these substances don't diffuse out of the blood because there is no concentration gradient. There is no urea in the dialysis fluid, so the urea is filtered out of the blood along the concentration gradient. Blood cells and large proteins can't move through the partially permeable membrane because they are too large. Dialysis restores the concentration of substances in the blood back to normal, but needs to be carried out at regular intervals. If a kidney becomes available, the patient may have a kidney transplant. If this is successful, the patient won't need any more dialysis treatments.
For most patients, a kidney transplant is a better option than dialysis. The diseased kidney gets replaced with a healthy one from a donor. Kidneys may be obtained from a victim of a fatal accident or sometimes from living donors. The new kidney must be a close tissue match to prevent immediate rejection. There are proteins called antigens on the surface of the cells. The recipient's antibodies may attack the antigens on the donor organ…