B3.3 HOMEOSTASIS

a) Waste products that have to be removed from the body include CARBON DIOXIDE produced by respiration and removed via the lungs when we breathe out and UREA produced in the liver by the breakdown of amino acids and removed by the kidneys in the urine, which is temporarily stored in the bladder. 

b) If the water or ion content of the body is wrong, too much water may move into or out of the cells and damage them. Water and ions enter the body when we eat and drink. 

c) A healthy kidney produces urine by: first filtering the blood, reabsorbing all the sugar, reabsorbing the dissolved ions needed by the body, reabsorbing as much water as the body needs and releasing urea, excess ions and water as urine. 

d) People who suffer from kidney failure may be treated either by using a kidney dialysis machine or by having a healthy kidney transplanted. 

e) Treatment by dialysis restores the concentration of dissolved substances in the blood to normal levels and has to be carried out at regular intervals. 

f) In a dialysis machine a person's blood flow between partially permeable membranes. The dialysis fluid contains the same concentrations of useful substances as the blood. This ensures that glucose and useful mineral ions are not lost. Urea passes out from the blood into the dialysis fluid. 

g) In kidney transplants a diseased kidney is replaced with a healthy one from a donor. However, the donor kidney may be rejected by the immune system unless precautions are taken. 

h) Antigens are proteins on the surface of cells. The recipient's antibodies may attack the antigens on the donor kidney as they do not recognise them as part of the recipient's body. 

i) To prevent rejection of the transplanted kidney: a donor kidney with a 'tissue-type' similar to that of the recipient is used and the recipient is treated with drugs that surpress the immune system. 

a) Sweating helps to COOL the body. More water is lost when it is hot, and more water has to be taken as drink or in food to balance this loss. 

b) Body temperature is monitored and controlled by the thermoregulatory centre in the brain. This centre has receptors sensitive to the temperature of the blood flowing through the brain. 

c) Also temperature receptors in the skin send impluses to the thermoregulatory centre, giving information about skin temperature. 

d) If the core body temperature is too high: blood vessels supplying the skin capillaries dilate so that more blood flows through the capillaries and more heat is lost; sweat glands release more sweat which cools the body as it evaporates. 

e) If the core body temperature is too low: blood vessels supplying the skin capillaires constrict to reduce the flow of blood through capillaries; muscles may 'shiver'-their contraction needs respiration, which releases some energy to warm the body. 

a) The blood glucose concentration of the body is monitored and controlled by the pancreas. The pancreas produces the hormone insulin, which allows the glucose to move from the blood into the cells. 

b) A second hormone, glucagon, is produced in the pancreas when blood glucose levels fall. This causes glycogen to be converted into glucose and be released into the blood. 

c) Type 1 diabetes is a disease in which a person's blood glucose concentration may rise to a high level because the pancreas does not produce enough of the hormone insulin. 

d) Type 1 diabetes may be controlled by careful attention to diet, exercise, and by injecting insulin.