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Removing waste products

Waste products must be removed from the body. If they are not, they will increase in concentration and may interfere with chemical reactions or damage cells.

Waste products that must be removed include carbon dioxide and urea.

carbon dioxide

  • product of aerobic respiration
  • removed through lungs when we breathe


  • produced in the liver when excess amino acids are broken down
  • removed by kidneys from the blood and make urine, which is stored in bladder
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Controlling blood glucose-The pancreas and insulin

the blood glucose concentration is controlled to provide cells with a constant supply of energy

The pancreas monitors and controls the concentration of glucose in the blood.

It produces a hormone called insulin. Insulin causes glucose to move from the blood into cells. It lowers the blood glucose concentration if it has become too high. This can happen after eating a meal that is rich in carbohydrates (for example, sweets, potatoes, bread, rice or pasta).

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Diabetes is a disease where the concentration of glucose in the blood is not controlled properly by the body. In type 1 diabetes, the pancreas does not produce enough insulin. This can lead to high levels of glucose in the blood, which can be fatal.

 Doctors, Frederick Banting and Charles Best, made an extract from the pancreas in 1921, it  had anti-diabetic properties, and they tested it on diabetic dogs. The first tests in humans were carried out in 1922, and was successful. .The extract contained the hormone insulin.

There are two types of treatment for diabetes:

  • Careful monitoring of food intake, with particular care taken over carbohydrates - which are digested into glucose.
  • Injecting insulin into the blood before meals. The extra insulin causes glucose to be taken up by the liver and other tissues. Cells get the glucose they need for respiration, and the blood glucose concentration stays normal.
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controlling body temperature-HOT

Diagram shows a cross section of skin when hot. Hair muscles relax (D) causing hairs to lie flat so that heat can escape. Sweat is secreted (E) from the sweat glands. Blood flow in the capillaries is increased (F) (http://www.bbc.co.uk/schools/gcsebitesize/science/images/hairs_hot.gif)

  • Sweat glands in the skin release more sweat. This evaporates, removing heat energy from the skin.
  • Blood vessels leading to the skin capillaries become wider - they dilate - allowing more blood to flow through the skin, and more heat to be lost.

D- Hair muscles relax. Hairs lie flat so heat can escape, E - Sweat secreted by sweat glands. Cools skin by evaporation, F - Blood flow in capillaries increases

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controlling body temperature-COLD

Diagram shows cross section of skin when cold, with erect hairs (B) caused by tense hair muscles (A), and reduced blood flow to capillaries (C)  (http://www.bbc.co.uk/schools/gcsebitesize/science/images/hairs_cold.gif)

Muscles contract rapidly - we shiver. These contractions need energy from respiration, and some of this is released as heat.

  • Blood vessels leading to the skin capillaries become narrower - they constrict - letting less blood flow through the skin and conserving heat in the body.
  • A - Hair muscles pull hairs on end,B - Erect hairs trap air,C - Blood flow in capillaries decreases.
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