Question 5a (iii)
Outline the role of insulin when the glucose concentration in the
blood increases. [5]
Detection of High Blood Glucose:
- Pancreatic Beta Cells in the islets of Langerhans detect an increase in blood glucose levels.
- Release of Insulin:
- In response, beta cells secrete insulin into the bloodstream to help lower the elevated glucose levels.
- Stimulating Glucose Uptake by Cells:
- Insulin binds to insulin receptors on the surface of target cells (especially in muscle and adipose tissue).
- This binding promotes glucose uptake by increasing the number of glucose transporters (GLUT4) on cell membranes, allowing glucose to enter cells more effectively.
- Glycogenesis in the Liver:
- Insulin stimulates the liver to convert excess glucose into glycogen (a storage form of glucose) through a process called glycogenesis.
- This reduces blood glucose concentration by storing glucose within liver cells.
- Inhibition of Gluconeogenesis:
- Insulin also inhibits gluconeogenesis (the production of new glucose) and glycogenolysis (breakdown of glycogen to glucose) in the liver.
- This prevents additional glucose from being released into the blood, further stabilizing glucose levels.
Summary
- Insulin plays a key role in lowering blood glucose by:
- Inhibiting glucose production, helping to maintain homeostasis when blood glucose rises.
- Promoting glucose uptake by cells,
- Stimulating glycogenesis in the liver,