BLOOD SUGAR REGULATION

 

 

The islets of the pancreas regulate glucose concentration

 

In addition to secreting digestive enzymes, the pancreas is an important endocrine gland. Its hormones, insulin and glucagon, are secreted by cells that form little clusters, the islets of Langerhans, throughout the pancreas. About one million islets are present in the human pancreas. They are composed of beta cells, which secrete insulin and alpha cells, which secrete glucagon.

 

 

Insulin lowers the concentration of glucose in the blood

 

Insulin stimulates cells of many tissues, including muscle and fat cells, to take up glucose from the blood. Once glucose enters muscle cells, it is either used immediately as fuel or is stored as glycogen. Insulin also inhibits the liver cells from releasing glucose. Thus, insulin activity results in lowering the glucose level from the blood.

 

 

Glucagon raises the concentration of glucose in the blood

 

 

The actions of glucagons are the opposite to those of insulin. The main effect of glucagons is to raise blood sugar levels. It does this by stimulating liver cells to both convert glycogen into glucose and to make glucose from other metabolites. Glucagon mobilises fatty acids and amino-acids as well as glucose.

 

 

Insulin and glucagon secretions are regulated by glucose concentration

Insulin abd glucagon secretions are directly controlled by the concentration of glucose in the blood. After a meal, when blood concentration rises as a result  of intestinal absorption, beta cells are stimulated to increase insulin production. Then, as cells remove glucose from the blood, decreasing its concentration, insulin secretion decreases accordingly, as follows:

Text Box: Blood glucose concentration too high     stimulates beta cells   insulin secretion increases blood glucose concentration decreases

 

 

 When one has not eaten for several hours, the concentration of glucose in the blood begins to fall. When it falls from its normal fasting level of about 90 mg of glucose per 100 mL of blood to about 70 mg of glucose, the alpha cells of the islets of Langerhans increase their secretion of glucagon. Glucose is mobilised from storage in the liver cells, and blood sugar concentration returns to normal:

 

 stimulates alpha cells glucagon secretion increases blood glucose concentration increases

Text Box: Blood glucose concentration too low  stimulates alpha cells glucagon secretion increases blood glucose concentration increases

 

 

 Insulin and glucagon work antagonistically.

 

Blood sugar regulation concept map