How are blood glucose levels controlled in the body?

When there is an excess of glucose in the blood (as there would be after eating a meal), the increase in blood glucose concentration is detected by the beta cells of the islets of Langerhans in the pancreas. They respond by increasing the secretions of the hormone insulin.

Insulin will increase the rate of glucose uptake by activating enzymes that convert glucose to glycogen, so blood glucose levels will lower and return to normal. This process is called glycogenesis.

Low blood glucose levels are detected by alpha cells of the islets of Langerhans of the pancreas. These cells will respond by increasing the secretions of glucagon into the blood.

Glucagon is a hormone that will activate enzymes in the liver, these enzymes will convert glycogen to glucose in a process called glycogenolysis. Glucagon will also stimulate formation of new glucose molecules in a process called gluconeogenesis. As more glucose is synthesised and released into the blood, the blood glucose levels will return to normal.

This system is controlled by negative feedback, once blood glucose concentrations have returned back to the normal level, the receptors involved will detect this and stop secreting excessive amounts of hormone (insulin or glucagon).

This process provides homeostasis; the maintainance of a constant internal environment and independance of fluctuating external conditions. Homeostasis is achieved by negative feedback.