6.4.3 Insulin

How Insulin Works

1. Detection of Glucose Rise:

• A rise in blood glucose concentration is detected by beta cells in the pancreas.

2. Secretion of Insulin:

• Beta cells secrete insulin, which inhibits the action of alpha cells that release glucagon.

3. Target Cells:

• Insulin travels in the blood and binds to receptors on target cells such as:
• Hepatocytes (liver cells)
• Muscle cells
• Adipose (fat) cells

4. Binding to Receptors:

• The binding of insulin to receptors on the plasma membrane activates the enzyme adenyl cyclase, which converts ATP into cyclic AMP (cAMP).
• This triggers a cascade of intracellular reactions.

Effects of Insulin:

1. Increased Glucose Uptake:

• More glucose transporter proteins are inserted into the cell membrane, increasing the uptake of glucose into the cells via facilitated diffusion.

2. Conversion of Glucose:

• Glucose is converted into glycogen in liver and muscle cells (glycogenesis).
• Glucose is converted into fat in adipose cells.

3. Increased Glucose Use:

• Glucose is used for cellular respiration in muscle and other tissues.

4. Reduced Glucose Release:

• Inhibits processes that increase blood glucose, such as glycogenolysis (breakdown of glycogen) and gluconeogenesis (formation of glucose from non-carbohydrate sources).

Summary of Insulin's Role in Lowering Blood Glucose Levels:

• Promotes glucose uptake by cells.
• Encourages glycogenesis and fat storage.
• Inhibits glycogenolysis and gluconeogenesis.