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  • Created by: Katherine
  • Created on: 15-03-13 18:59


Homeostasis is the maintenance of a consistant internal environment.

Homeostasis controls:

  • The Body Temperature
  • Water Content
  • Ion Content
  • Blood Sugar Levels
  • Removel of Carbon Dioxide and Urea
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Temperature Control

The enzymes within the human body work best at 37'C

If the body gets too hot or too cold, the enzymes won’t work properly and important reactions could be disrupted, even leading to death.

Body temperature is monitored and controlled by the thermoregulatory centre in the brain. It contains receptors sensitive to the temperature of the blood flowing through the brain.

Temperature receptors in the skin also send impulses to the thermoregulatory centre, giving information about skin temperature.

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If The Core Body Temperature Is Too High:

  • The blood vessels supplying the skin dilate so more blood flow throught the capillaries close to the surface of the skin. This makes the transfer of heat from the blood to the environment easier.
  • Sweat glands release more sweat which cools the body as it evaporates.
  • Hairs lie flat


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If The Core Body Temperature Is Too Low:

  • Blood vessels supplying the skin capillaries constrict to reduce the flow of blood through the capillaries.
  • No sweat is produced.
  • Hair stands up to trap an insulating layer of air.
  • Muslces may 'shiver' - their contractions need repiration, which releases some enregy that warms the body up.
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Removal Of Waste Products

Carbon Dioxide:

  • Produced by repiration
  • Removed via the lungs when we breathe out


  • Produced by the breakdown of amino acids in the liver and release into the bloodstream.
  • It is poisonus, so the kidneys filter it out from the blood and temporarily store it in the bladder in urine.
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Water and Ion Control

  • Ions (e.g. sodium) and water enter the body when we eat or drink.
  • If the ion or water content of the body is worng, too much water may move in or out of our cells by osmosis, which can damage cells.


  • Excess ions are removed by the kidneys.
  • Some ions are also lost in sweat - why it tastes salty
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Water and Ion Control


  • Water is lost from the body in:
    • sweat
    • urine
    • the air we breathe out
  • Water is balanced between: 
    • liquids consumed
    • amount sweated out
    • amount excreted by the kidneys in the urine.
  • Lost water must be replaced with water from food and drink to restore the balance.
  • Cold -> Sweat less -> more urine (pale & dilute)
  • Warm -> Sweat more -> less urine (dark-coloured & concentrated)
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Sports Drinks

Sports drinks (and soft drinks) contain sugar, water and ions.

The sugar replaces sugar used in energy released during the activity

The water and ions replace those lost during sweating

If the water and ions are not replaced, the ion/water balance of the body is disturbed and the cells do not work as efficiently.

Manufactures Claim Their Products:

  • Rehydrate you faster than plain water
  • Improve your endurance


  • Is the report a scientific study, published in a reputable journal?
  • Was it written by a qualified person, not connected to the seller?
  • Large enough sample size?
  • Other studies obtained similar results?
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Sugar Control

Eating foods containing carbohydrates put glucose into the blood from the gut.

Vigorous exercise and the normal metabolism of cells removes glucose from the body.

Levels of glucose in the blood is controlled as part of homeostasis and must be kept the steady. 

The blood glucose concentration of the body is monitored and controlled by the pancreas, using the hormones insulin and glucagon.

If the blood glucose level is too high insulin is secreated by the pancreas. Insulin makes the liver convert glucose into gycogen.

If the blood glucose level is too low glucagon is secreated by the pancreas. Glucagon makes the liver convert glycogen into glucose and release it into the blood.

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Type 1 Diabetes

Type 1 Diabetes is a disease in which a person's blood glucose concentration may rise to a high level that can kill them because the pancreas doesn't produce enough of the hormone insulin.

The problem can be controlled by:

  • Careful attention to diet. Avoiding foods rich in simple carbohydrates, i.e. sugars
  • Exercise after eating to try and use up extra glucose produced during digestion.
  • Injecting insulin into the blood at mealtimes
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Injecting Insulin

Injecting Insulin makes the liver remove the glucose as soon as it enters the blood from the gut, after digestion. This stops the level of glucose in the blood getting too high.

It is a very effective treatment.

The amount of insulin that needs to be injected depends on the person's diet and how active they are.

Insulin use to be extracted from the pancreas of pigs and coww, but now human insulin is made by genetic engineering. This human insulin doesn't cause adverse reactions in patients, like animal insulin did.

Insulin injections can't control glucose levels as accurately as having a normal working pancreas, so they may still have long-term health problems.

Insulin can't be taken in a pill as the enzymes in the stomach would destroy it before it enters the bloodstream.

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Pancreas Transplant

Diabetics can have a pancreas transplant, resulting in no further insulin injections. However the body can reject the tissue, and costly immune system suppressive drugs have to be taken, which have side-effects.

But modern research into artificial pancreases and stem cell research may mean the elimination of organ rejection.

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