7.13 - 7.14 - Blood glucose control
Explain how insulin lowers raised blood glucose by changing glucose uptake and storage. Higher learners also explain how glucagon raises low blood glucose and compare the two feedback responses.
7.13 - Insulin lowers raised blood glucose
Blood plasma transports dissolved glucose around the body. After a meal containing carbohydrate, digestion and absorption can raise the concentration of glucose in the blood. The pancreas responds to this rise by releasing the hormone insulin, which travels in the blood to its target tissues.
Insulin lowers a raised blood glucose concentration through two linked actions:
- Body cells take up more glucose from the blood. Cells can use glucose in respiration, which releases energy for cellular processes.
- Liver and muscle cells convert glucose to glycogen, an insoluble storage carbohydrate. This moves glucose out of the blood and into a stored form.
With less glucose remaining in the blood, its concentration falls back towards the usual level. As the deviation is corrected, insulin release decreases. This is negative feedback because the response opposes the original rise; insulin is the signal that causes the response, not a substance that turns into glycogen.
Raised blood glucose -> pancreas releases insulin -> glucose leaves the blood for cell uptake and glycogen storage -> blood glucose falls towards the usual level.
7.14 - Glucagon and two-way control
Higher tier extension (7.14). Insulin explains the response to a rise. A fall in blood glucose concentration needs the opposite route. The pancreas responds to a lowered concentration by releasing glucagon into the blood.
Glucagon acts mainly on the liver. It causes stored glycogen in liver cells to be converted to glucose, and the liver releases that glucose into the blood. Glucose therefore moves from the liver into the blood, so blood glucose concentration rises towards the usual level. As the concentration recovers, glucagon release decreases.
| Starting deviation | Hormone | Target response | Movement across the blood boundary | Result |
|---|---|---|---|---|
| Blood glucose too high | Insulin | Body cells take up glucose; liver and muscle store glucose as glycogen | Glucose leaves the blood | Blood glucose falls |
| Blood glucose too low (Higher only) | Glucagon | Liver converts glycogen to glucose | Glucose enters the blood from the liver | Blood glucose rises |
Muscle may store glycogen, but in this GCSE feedback route the liver is the source that releases glucose into the blood under glucagon control. The two hormones are not changed into one another: each carries a different signal from the pancreas to target tissue.
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