6.8 - Regulating Blood Glucose

Why blood glucose is controlled

Body cells need the amount of glucose (a sugar) in the blood kept steady - too much or too little stops cells working properly and can be dangerous to health.

How glucose enters and leaves the blood

• Glucose in - Enters the blood from the gut whenever carbohydrate-containing food is digested and absorbed in the small intestine.
• Glucose out - Removed by the normal metabolism of cells, which use glucose in respiration; much more is removed during vigorous exercise.

Storing excess glucose

1. Excess glucose is converted to glycogen (a storage carbohydrate) and kept in the liver and the muscles.
2. Once those stores are full, the rest is stored as lipid (fat) in the tissues.

The pancreas monitors blood glucose

• Because glucose is constantly going into and out of the blood, its concentration would swing up and down without a control system.
• The pancreas does the controlling: it constantly monitors the concentration of glucose in the blood and responds to keep it within a narrow, healthy range.

Insulin lowers blood glucose

1. When blood glucose concentration rises too high - for example after a meal containing carbohydrate - the pancreas detects the change.
2. The pancreas responds by secreting the hormone insulin (a protein) into the blood.
3. Insulin travels in the blood to its target organs: the liver and the muscles.

How insulin lowers blood glucose

• Insulin makes glucose move out of the blood and into the liver and muscle cells.
• In these cells, the glucose is used:
  • Some is respired
  • The excess is converted into glycogen and stored
• Because glucose is taken out of the blood and locked away as glycogen, the blood glucose concentration falls back towards normal.
• The key point about insulin is that it lowers blood glucose concentration - it brings a high level down, rather than simply "controlling" it.