Students should be able to explain how insulin controls blood glucose…

The idea

To explain insulin control, describe a complete negative feedback sequence. After a meal, glucose absorbed into the blood raises blood glucose concentration. The pancreas detects this rise and secretes insulin into the blood. Insulin travels to liver and muscle cells and increases the permeability of their cell membranes to glucose, so glucose moves from the blood into the cells. Inside the cells, glucose is used in respiration and any excess is converted to glycogen for storage. As glucose leaves the blood, blood glucose concentration falls back towards its normal set point. When the concentration becomes too low, the pancreas secretes glucagon, which stimulates the breakdown of glycogen to glucose, raising blood glucose concentration again.

What earns the marks

• A rise in blood glucose concentration is detected by the pancreas.
• The pancreas secretes insulin into the blood.
• Insulin increases the movement of glucose from the blood into liver and muscle cells.
• Insulin increases the permeability of cell membranes to glucose.
• Excess glucose inside cells is converted to glycogen for storage.
• The removal of glucose from the blood lowers blood glucose concentration towards the set point.
• A fall in blood glucose concentration triggers glucagon, which releases glucose from glycogen.

Common mistakes and how to put them right

• Describing only that insulin lowers blood glucose without explaining how cells take up glucose.

  Put it right: Include the effect on cell membranes and the movement of glucose into cells.

• Treating insulin and glucagon as if they are secreted at the same time.

  Put it right: Insulin responds to a rise and glucagon responds to a fall in blood glucose concentration.

• Omitting the role of the liver and muscles.

  Put it right: Name these target cells and their role in storing glucose as glycogen.

Exam tips

• Write the explanation as a sequence: stimulus, detection, hormone secretion, target cell response, effect on blood glucose concentration.
• Use the term negative feedback and make clear that the response reverses the original change.
• Include both the uptake of glucose into cells and the storage of excess glucose as glycogen to show full understanding.