Blood glucose rises after carbohydrate
Definition
Blood glucose concentration
The amount of glucose dissolved in a given volume of blood.
- Blood glucose concentration is the amount of glucose dissolved in a given volume of blood.
- Carbohydrate digestion produces glucose, which is absorbed through the small intestine into the blood.
- After a meal the absorbed glucose makes blood glucose concentration rise.
- Between meals and during exercise cells remove glucose from the blood for respiration, so the concentration falls.
- Control keeps the concentration within a narrow range so cells receive glucose without large changes to the water balance of the blood.
Insulin lowers high blood glucose
Definition
Insulin
A hormone released by the pancreas when blood glucose concentration is too high that causes body cells to take in glucose and causes liver and muscle cells to convert glucose into glycogen.
- Detection occurs when the pancreas senses that blood glucose concentration is above the normal range.
- Release follows as the pancreas secretes insulin into the blood plasma.
- Transport occurs in the plasma, which carries insulin to target cells and organs including the liver.
- Cell uptake increases because insulin causes body cells to take more glucose from the blood.
- Storage increases because insulin causes liver and muscle cells to convert glucose into glycogen.
- Correction occurs as glucose leaves the blood, returning blood glucose concentration towards the normal range.
- The control pathway can be written as high blood glucose→insulin release→glucose uptake and glycogen formation→blood glucose falls\text{high blood glucose} \rightarrow \text{insulin release} \rightarrow \text{glucose uptake and glycogen formation} \rightarrow \text{blood glucose falls}high blood glucose→insulin release→glucose uptake and glycogen formation→blood glucose falls.
Example
Following a blood glucose peak
- A graph rises from 5.0 mmol dm−35.0\,\mathrm{mmol\,dm^{-3}}5.0mmoldm−3 before a meal to 8.0 mmol dm−38.0\,\mathrm{mmol\,dm^{-3}}8.0mmoldm−3 afterwards, so the pancreas releases more insulin.
- Insulin acts on body cells and the liver, increasing glucose uptake and conversion of glucose to glycogen.
- The graph falls because glucose is removed from the blood, so the concentration returns towards its starting range.
Glycogen stores excess glucose
Definition
Glycogen
An insoluble carbohydrate made from glucose and stored mainly in liver and muscle cells.
- Glycogen is an insoluble carbohydrate made from many glucose units and stored mainly in liver and muscle cells.
- Insolubility allows a large amount of glucose to be stored without the glycogen dissolving and strongly affecting water movement into the cell.
- Liver glycogen provides a store that can later supply glucose to the blood when the concentration becomes too low.
- Muscle glycogen provides glucose for respiration in muscle cells during activity.
Common Mistake
Do not write that insulin breaks glucose down, because insulin lowers blood glucose by increasing uptake and storage while respiration is a separate process.
Insulin release falls after correction
Definition
Negative feedback
A control mechanism in which a change away from the normal level causes responses that reverse the change and restore the normal level.
- Negative feedback means that a change away from the normal level causes responses that reverse the change.
- As blood glucose falls the stimulus for insulin release becomes weaker, so less insulin is released.
- When the normal range is restored the corrective response is reduced rather than continuing to drive the concentration lower.
Exam technique
Writing an insulin explanation
- Start with the stimulus: state that blood glucose concentration is too high and the pancreas releases insulin.
- Give the target response: state that body cells take in more glucose and liver or muscle cells convert glucose into glycogen.
- Finish with the outcome: state that removing glucose from the blood lowers its concentration towards the normal range.
- Keep the carrier accurate: hormones travel dissolved in blood plasma, not inside red blood cells.
Self review
- What change causes the pancreas to release insulin?
- How is insulin transported to its target organs?
- How does insulin change the behaviour of body cells?
- What happens to glucose in liver and muscle cells?
- Why does insulin release fall when blood glucose returns to normal?
