Mechanism of Insulin Secretion

OCR A-level BiologyHormonal CommunicationLesson 10 of 11

When the blood glucose concentration is normal, ATP-sensitive potassium channels are open. Potassium ions diffuse out of the beta cells. The inside of the cell is -70mV relative to the outside of the cell.
When blood glucose concentrations rise glucose enters the cell by glucose transporters.
Glucose is used in respiration inside the mitochondria leading to a rise in the amount of ATP.
ATP binds to the ATP-sensitive potassium channels and they close.
Potassium ions are no longer able to diffuse out of the cell. Depolarisation occurs as the potential difference rises to about -30mV
Depolarisation causes voltage-gated calcium in channels to open.
The entry of calcium ions into the cell causes secretory veisicls to fuse with the membrane and release insulin by exocytosis.

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Depolarisation: A change in the potential difference across a membrane that makes the inside less negative, caused by an influx of sodium ions.
Insulin: A hormone secreted by beta cells of the islets of Langerhans in response to high blood glucose concentration that increases the uptake of glucose by cells.
ATP: Adenosine triphosphate, the universal energy currency of cells, which releases energy for cellular reactions when hydrolysed to ADP and inorganic phosphate.