The concentration of glucose in the blood must be kept at a set point. The concentration of glucose in a person’s blood can increase after they have eaten a meal containing lots of carbohydrates. The concentration of glucose in a person’s blood can decrease after a period of exercise or if they have not eaten for a long while. Glucose diffuses out of the blood into muscle cells and is broken down to release energy for muscle contractions.
If the blood glucose concentration rises too high then cells can lose water. This may interfere with cell activities.
If the blood glucose concentration falls too much then body cells will not receive as much glucose and so will not be able to release so much energy in respiration.
The liver acts as the body’s glucose 'reservoir'. When the blood glucose concentration gets too high liver cells can take in glucose and store it. When the blood glucose concentration gets too low liver cells can release glucose into the blood.
The diagram below shows how the concentration of glucose in the blood is regulated.