The concentration of blood glucose is maintained by a negative feedback process involving two hormones insulin and glucagon.
- Insulin is a small peptide (protein) hormone.
- β (beta) cells of the islets of Langerhans in the pancreas secrete insulin. The secretion is triggered by an increase in the concentration of circulating glucose ("blood sugar").
- Insulin stimulates liver cells to take up glucose from the blood and convert it into glycogen. (It also stimulates skeletal muscle to take up glucose and convert it into glycogen). The stimulation occurs because the insulin molecules bind to receptors on the surface of liver cells which cause facilitated diffusion proteins to open and therefore glucose enters the cells.
All of these actions result in the storage of the soluble nutrients absorbed from the intestine into an insoluble product (glycogen).
- Glucagon is also a protein hormone
- α (alpha) cells of the islets of Langerhans in the pancreas secrete glucagon
- glucagon secretion is triggered by a low concentration of glucose in the blood
- glucagon acts principally on the liver where it stimulates the conversion of glycogen into glucose which is released into the bloodstream.
The physiological significance of this is that glucagon functions to maintain a steady concentration of blood sugar level between meals, and during prolonged exercise.
This process is summarised by the flowchart below
|Figure 1 : Blood glucose regulation