AQA Biology 3 - Homeostasis

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Humans need to remove waste products from their bodies to keep their internal environment relatively constant. People whose kidneys do not function properly may die because toxic substamces accumulate in their blood. Their lives can be saved by usuing dialysis machines or having a healthy kidney transplanted. Water and ion content, body temperature and blood glucose levels must be kept within very narrow ranges.

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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.

*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.

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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.

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A healthy kidney produces urine by:

1- first filtering the blood

2- reabsorbing the sugar

3- reabsorbing the dissolved ions needed by the body

4- reabsorbing as much water as the body needs

5- releasing urea, excess ions and water as urine

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

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

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In a dialysis machine a person's blood flows between partially permeable membranes. The dialysis fluid contains the same concentration of useful substamces as the blood. This ensures that glucose and useful mineral ions are not lost. Urea passes out from the blood inot the dialysis fluid.

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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.

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

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To prevent rejection of the transplanted kidney:

*a donor kidney with a 'tissue-type' similar to that of the recipent is used

*the recipent is treated with drugs that suppress the immune system

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