Explain how blood glucose concentration is regulated by glucagon

The idea

Glucagon is a hormone released by the pancreas when blood glucose falls too low. Pancreatic cells detect the low concentration and secrete glucagon into the blood. Glucagon travels to the liver, where it binds to liver cells and stimulates the conversion of stored glycogen into glucose. The glucose is released from the liver cells into the blood, so blood glucose concentration rises back towards the normal range. This is an example of negative feedback: the corrective response reverses the original change. Glucagon therefore works in the opposite direction to insulin, which lowers blood glucose when it is too high. A useful method is to trace the pathway in order: low glucose detected → glucagon secreted by pancreas → glucagon carried in blood to liver → glycogen converted to glucose → glucose released into blood → concentration rises.

What earns the marks

• Glucagon is secreted by the pancreas when blood glucose concentration falls below the normal range.
• Glucagon is transported in the blood to the liver, where it acts on liver cells.
• Glucagon stimulates the conversion of glycogen stored in the liver into glucose.
• The glucose produced is released from the liver into the blood, raising blood glucose concentration back towards normal.
• The response is an example of negative feedback, reversing the fall in blood glucose; glucagon has the opposite effect to insulin.

Common mistakes and how to put them right

• Saying glucagon is released when blood glucose is too high.

  Put it right by stating glucagon is released when blood glucose falls too low, whereas insulin is released when it is too high.

• Saying glucagon converts glucose into glycogen.

  Put it right by stating glucagon stimulates the breakdown of glycogen into glucose in the liver.

• Saying glucagon is made in the liver.

  Put it right by stating glucagon is secreted by the pancreas and acts on the liver.

Exam tips

• Name the organ that secretes glucagon (the pancreas) and the organ it acts on (the liver) explicitly in your answer.
• Describe the direction of change: glucagon raises blood glucose, so state that the concentration rises back towards normal.
• Use the term glycogen correctly and link its conversion to glucose release into the blood.