IGCSE Biology / Chemical coordination
Insulin, glucagon and the pancreas
Edexcel International GCSE Biology (4BI1), chapter 7: Chemical coordination, specification point 2.94. Free lesson.
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The pancreas helps keep blood glucose concentration steady by releasing insulin or glucagon. These hormones have opposite effects, and you can use their actions to explain changes on a blood glucose graph.
How the pancreas and liver control blood glucose
This is a negative feedback system: a change in blood glucose triggers a response that brings it back towards normal. The pancreas detects the change, while the liver carries out much of the response. The pancreas detects whether blood glucose is too high or too low. The liver stores glucose or releases it, depending on which hormone the pancreas releases.
What happens when blood glucose is too high
After a meal, glucose from digested food is absorbed into the blood, so blood glucose rises above normal. The pancreas releases insulin into the blood. Insulin causes the liver and muscles to take up glucose and convert it into glycogen for storage. Blood glucose then falls towards normal, and the pancreas stops releasing insulin.
What happens when blood glucose is too low
Between meals or during exercise, blood glucose can fall below normal. The pancreas releases glucagon instead of insulin. Glucagon makes the liver break down stored glycogen into glucose, which enters the blood and raises blood glucose towards normal.
How to explain a blood glucose graph
After a meal, the graph rises steeply because glucose is absorbed from the small intestine into the blood. Insulin causes the later fall by helping glucose to be stored as glycogen. Blood glucose may dip slightly below normal before glucagon brings it back up. The rise after a meal is caused by absorption of glucose from digested food, not by insulin. The fall is caused by insulin promoting storage as glycogen. If the line undershoots normal, glucagon raises blood glucose again.
Keep insulin and glucagon the right way round
The hormone names are similar, but their effects are opposite. Insulin puts glucose in to storage. Glucagon gets glucose back out of glycogen. Releasing glucagon when blood glucose is already high would raise it further and make the problem worse. High blood glucose: insulin, so glucose is stored as glycogen. Low blood glucose: glucagon, so glycogen is broken down into glucose.