Homeostasis in Action

Controlling Body Temperature

- body temperature is monitored and controlled by the thermoregulatory centre in your brain, the thermoregulatory centre contains receptors sensitive to the temperature of the blood

- the skin also contains temperature receptors and sends nerve impluses to the thermoregulatory centre

- if the body temperature is too high, blood vessels dilate (vasodilation) and sweat is produced from the sweat glands, both cause a transfer of energy from the skin to the environment

- if the body temperature is too low, then the blood vessels constrict (vasoconstriction) and sweating stops, reducing the transfer of energy to the environment

- skeletal muscles contract (shiver) and the exothermic reactions of respiration needed for muscle contraction raise the temperature

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Removing Waste Products

- water leaves the body via the lungs during exhalation

- water, miner ions and urea are lost through the skin in sweat

- there is no control over water, mineral ion or urea loss by the lungs or skin

- urea, along with excess water and mineral ions, is removed via the kidneys in the urine, the loss of mineral ions and water is carefully balanced by the body

- if the body cells lose or gain too much water by osmosis, they do not function efficiently

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Human Kidney

- the kidneys are important for excretion and homeostasis

- a healthy kidney produces urine by filtering the blood, it then reabsorbs all of the glucose, plus any mineral ions and water needed by your body

- excess mineral ions and water, along with urea are removed in the urine

- the water balance of the blood is maintained by the hormone ADH, which changes the amount of water reabsorbed by the kidney tubules

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Dialysis- Artificial Kidney

- people with kidney failure may be treated by regular sessions on a kidney dialysis machine or by having a kidney transplant

- in a dialysis machine, the concentration of dissolved substances in the blood is restored to normal levels

- the levels of useful substances in the blood are maintained, while urea and excess mineral ions pass from the blood into the dialysis fluid

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Kidney Transplants

- in a kidney  transplant, a healthy kidney from a donor replaces the function of the diseased or damaged kidney

- to try and prevent rejection of the donor kidney, the tissue types of the donor and the recipient are matched as closely as possible,

    immunosuppressant drugs are also used

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