Answer
The hormone insulin is a protein/peptide hormone that is secreted by the beta cells of the Islets of Langerhans of the pancreas. It promotes glucose uptake by tissues.
Work Step by Step
After a meal the blood glucose level rises. This triggers the release of insulin from the beta cells of the pancreas. Insulin acts on cells to increase their capacity to absorb glucose. This is of particular importance in muscles, liver and adipose tissues. This absorbed glucose is stored as an energy source in the form of glycogen or fat.
Four or five hours after a meal, the blood glucose level will be low. This is the trigger for the alpha cells of the Islets of Langerhans (pancreas) to release the hormone glucagon. Glucagon has the opposite effects of insulin. It increases the availability of glucose in three ways:
1. Increased gylcogenolysis -- the breakdown of glycogen to give glucose molecules
2. Decreased glycogenesis--decrease in glycogen synthesis
3. Increased gluconeogenesis-- synthesis of new glucose molecules
Energy stored in fats is also made available, for glucagon also promotes lipolysis.
