Blood glucose concentration is monitored and controlled by the pancreas.

The idea

The pancreas acts as the body's glucose sensor and control centre. Cells in the pancreas detect changes in the concentration of blood glucose. When the concentration rises after a meal, the pancreas releases the hormone insulin. Insulin travels in the blood and causes cells, mainly liver and muscle cells, to take up glucose, converting it to glycogen for storage. Glucagon targets the liver (not muscle cells), causing glycogen to be converted back into glucose and released into the blood. This negative feedback system keeps blood glucose within a narrow range.

What earns the marks

• The pancreas monitors and controls blood glucose concentration.
• If blood glucose is too high, the pancreas secretes insulin.
• Insulin causes glucose to move from the blood into cells, and liver and muscle cells convert excess glucose into glycogen.
• (HT only) If blood glucose is too low, the pancreas secretes glucagon.
• (HT only) Glucagon causes the liver to convert stored glycogen into glucose, which is released into the blood.

Common mistakes and how to put them right

• Stating that insulin breaks down glucose.

  Put it right by explaining that insulin causes cells to take up glucose and convert it to glycogen.

• (HT only) Thinking glucagon acts on muscle cells.

  Put it right by specifying that glucagon targets the liver to convert glycogen to glucose.

• Describing the pancreas as filtering glucose out of the blood.

  Put it right by stating the pancreas detects glucose levels and secretes hormones.

Exam tips

• Always specify that insulin causes glucose to be converted to glycogen in the liver and muscle cells.
• (HT only) Clearly distinguish between glycogen (the storage carbohydrate) and glucagon (the hormone).