Glucose Metabolism
Energy is required for the normal functioning of the organs of the body. The most important cellular energy source is glucose. Many tissues can also use fat or protein as an energy source but others, such as the brain and red blood cells, can only use glucose.
Glucose is stored in the body as glycogen. The liver is an important storage site for glycogen. Glycogen is mobilized and converted to glucose by gluconeogenesis when the blood glucose concentration is low. Glucose may also be produced from non-carbohydrate precursors, such as pyruvate, amino acids and glycerol, by gluconeogenesis. It is gluconeogenesis that maintains blood glucose concentrations, for example during starvation and intense exercise.
The endocrine pancreas
The pancreas has both endocrine and exocrine functions. The endocrine tissue is grouped together in the islets of Langerhans and consists of four different cell types each with its own function:
- Alpha cells produce glucagon
- Beta cells produce proinsulin. Proinsulin is the inactive form of insulin that is converted to insulin in the circulation.
- Delta cells produce somatostatin
- F or PP cells produce pancreatic polypeptide
Regulation of insulin secretion
Insulin secretion is increased by:
- elevated blood glucose concentrations
- gastrointestinal hormones
- Beta adrenergic stimulation
Insulin secretion is inhibited by:
- catecholamines
- somatostatin
The role of insulin and glucagon in glucose metabolism
Insulin and glucagon work synergistically to keep blood glucose concentrations normal.
Insulin
An elevated blood glucose concentration results in the secretion of insulin: glucose is transported into body cells.
The uptake of glucose by liver, kidney and brain cells is by diffusion and does not require insulin.
Click on the icon for details on the effect of insulin:
Glucagon
The effects of glucagon are opposite to those of insulin.
Click on the icon for details on the effect of glucogon:
