The concentration of glucose in the blood is monitored and controlled by the pancreas. If the blood glucose concentration is too high, for example after a meal, the pancreas produces the hormone insulin. Insulin causes glucose to move from the blood into the cells. In liver and muscle cells, excess glucose is converted to glycogen for storage. The blood glucose concentration then falls back to normal.
Higher tier only: if the blood glucose concentration is too low, the pancreas produces the hormone glucagon. Glucagon causes glycogen to be converted back into glucose, which is released into the blood. Insulin and glucagon work together in a negative feedback cycle: a change in blood glucose triggers a response that reverses the change, keeping the level steady.
In Type 1 diabetes the pancreas fails to produce enough insulin. Blood glucose levels rise and stay uncontrollably high. It is normally treated with insulin injections.
In Type 2 diabetes the body cells no longer respond to the insulin that the pancreas produces. It is commonly treated with a carbohydrate controlled diet and an exercise regime. Obesity is a risk factor for Type 2 diabetes.
On a graph, a person without diabetes shows blood glucose rising after a meal and then falling back as insulin acts. A person with untreated Type 1 diabetes shows glucose that rises and stays high. After an insulin injection the level falls.
