Insulin (AQA A Level Biology): Revision Note

Blood glucose concentration varies due to factors such as:

• consumption of foods containing carbohydrates

• exercise

• secretion of hormones that affect blood glucose

Hormones that affect blood glucose levels include:

• insulin: reduces blood glucose

• glucagon: increases blood glucose

• adrenaline: increases blood glucose

These hormones form part of a negative feedback loop that maintains blood glucose levels within narrow limits

An increase in blood glucose concentration to a level that is above the normal range is detected by cells in the pancreas

In response to this stimulus β cells in the pancreas secrete the hormone insulin

Insulin causes a reduction in blood glucose as follows:

1. insulin binds to specific receptors on the membranes of target cells, e.g.:

   • liver cells

   • muscle cells

2. more glucose transporter proteins are added to the cell surface membranes of target cells, increasing their permeability to glucose

   • This is achieved when vesicles containing glucose transporters fuse with the cell surface membrane

3. glucose moves into target cells by facilitated diffusion

4. enzymes are activated that convert glucose into glycogen

   • This is glycogenesis