Free Control of Blood Glucose revision notes for OCR A Level Biology – covering specification point 5.1.4 (d).
Control of Blood Glucose
Blood glucose concentration is maintained around an optimal set point by negative feedback.
Alpha and beta cells in the islets of Langerhans monitor blood glucose concentration, which affects the rate at which they secrete glucagon and insulin (respectively).
The diagram below shows the negative feedback flowchart for blood glucose concentration:
Beta (β) Cells
β cells release insulin into the bloodstream in response to high levels of blood glucose.
Blood glucose is measured indirectly with the use of a glucose sensor, glucokinase, which alters the metabolic functioning of β cells.
When blood glucose concentration is high:
- Glucose diffuses into the β cell down its concentration gradient by facilitated diffusion.
- Glucokinase phosphorylates glucose into glucose-6-phosphate (G6P).
- G6P enters glycolysis and is oxidised into ATP.
- Many ATP molecules cause many K+ channels to close.
- K+ builds up inside the cell, reducing the potential difference.
- The β cell depolarises as the inside becomes less negative.
- Voltage-gated Ca2+ channels open.
- Ca2+ diffuses into the β cell down its concentration gradient.
- Ca2+ causes vesicles containing insulin to move towards the cell surface membrane.
- Insulin is released from the β cell by exocytosis.
Insulin travels through the bloodstream and binds to a complementary receptor on the cell surface membrane of target cells.
