A-Level Biology AQA Notes

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Control of Blood Glucose Concentration

Insulin is a hormone released from β-cells in the pancreas when blood glucose concentration rises in order to lower the concentration back to its optimum via negative feedback.
When insulin binds to an insulin receptor, vesicles of glucose transporters fuse with the plasma membrane to allow more glucose to enter the cell. The cell also uses more glucose in respiration and activated enzymes covert glucose into glycogen (glycogenesis).
Glucagon is a hormone released from α-cells in the pancreas in response to low glucose concentration in order to increase the concentration back to its optimum. It does this by:
- Activating enzymes which break down glycogen into glucose (glycogenesis).
- Producing glucose from other molecules
- Activating enzymes that convert glycerol (from lipids) and amino acids into glucose (gluconeogenesis)
Adrenaline is released by the adrenal glands in times of stress and increases blood glucose concentration in anticipation of increased activity.
Adrenaline binds to adrenaline receptors which activates adenyl cyclase. This converts ATP into cAMP, which acts as a second messenger to activate protein kinase. Protein kinase converts glycogen into glucose.

Diabetes

Diabetes is a condition where the concentration of glucose in the blood cannot be controlled effectively. It can lead to hyperglycaemia after meals and hypoglycaemia after exercising.
Type 1 diabetes is caused by an autoimmune attack on the β-cells of the pancreas, so the body cannot produce insulin. It can be treated by insulin injections.
Type 2 diabetes is caused because the body does not produce enough insulin & the insulin receptors become less responsive. It can be treated by lifestyle changes (losing weight & exercising), drugs to stimulate insulin production and reduce glucose absorption and insulin injections in severe cases.

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