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Glucose is needed in the blood to supply cells with glucose for respiration.

If blood glucose concentrations are too high, cells are damaged due to a loss of water by osmosis. The pancreas continually monitors the level of glucose in the blood.

How insulin works

The following steps show the different changes in the body before, during and after a meal is eaten:

1. Normal blood glucose concentration in the body.
2. Meal high in carbohydrate is eaten.
3. Blood glucose concentration increases (as glucose is absorbed from the ileum).
4. Pancreas makes insulin after detecting blood glucose increase.
5. Insulin acts in the liver to reduce blood glucose concentration by:
   • increasing glucose absorption from the blood by the liver and muscles;
   • converting excess glucose to glycogen which is stored mainly in liver but also muscle;
   • increasing respiration in the liver.
6. Normal blood glucose concentration is restored.

When blood glucose concentrations are low, less insulin is produced and the above processes do not take place or slow down.

This helps to raise the concentration of glucose in the blood.

Negative feedback

This is a mechanism to ensure the concentration of a substance does not deviate too far from normal.

These mechanisms usually involve a hormone and the continual monitoring of the substance being controlled, e.g. the pancreas adjusting the amount of insulin it makes depending on the blood glucose concentration.

It’s known as negative feedback because an increase in hormone decreases the substance being controlled, e.g. an increase in insulin decreases blood glucose concentration.