Explain how the hormone insulin controls blood glucose concentration

The idea

Insulin is secreted by the pancreas when blood glucose rises, for example after a meal. It travels in the blood and acts on target cells, especially the liver and muscles. It increases the uptake of glucose from the blood into cells and stimulates the conversion of glucose into glycogen for storage in the liver and muscles. As cells take up glucose and store it as glycogen, blood glucose concentration falls back towards normal. This is a negative feedback loop: the rise in glucose triggers insulin release, and the resulting fall reduces the stimulus. Glucagon has the opposite effect, but the question focuses on insulin. Link the hormone to its source, its target action and the resulting fall in blood glucose.

What earns the marks

• Insulin is secreted by the pancreas in response to a rise in blood glucose concentration.
• Insulin increases the uptake of glucose from the blood into cells such as liver and muscle cells.
• Insulin stimulates conversion of glucose to glycogen for storage in the liver and muscles.
• As glucose is taken up and stored, blood glucose concentration falls, reducing the stimulus (negative feedback).
• Identifies the pancreas as the source of insulin and the liver/muscles as target tissues.

Common mistakes and how to put them right

• Saying insulin raises blood glucose.

  Put it right: Correct it: insulin lowers blood glucose by promoting uptake and storage.

• Naming the liver as the source of insulin.

  Put it right: Correct it: the pancreas secretes insulin.

• Confusing glycogen with glucagon.

  Put it right: Correct it: glucose is stored as glycogen, while glucagon is a hormone with the opposite effect.

Exam tips

• State the source (pancreas), the action (uptake and conversion to glycogen) and the effect (blood glucose falls).
• Keep glycogen (storage carbohydrate) and glucagon (hormone) clearly distinct.
• Frame the answer as negative feedback: the response reduces the original rise in glucose.