Hormones that control the level of insulin in the body are insulin and glucagon. They work to maintain homeostasis via a negative feedback loop. This is where the level of one hormone stimulates or inhibits the production of a second hormone. The hormone insulin stimulates cells found in the muscles and in the liver to remove excess glucose in the blood and to store it as glycogen. When sugar is needed for energy, the hormone glucagon stimulates the liver to break down glycogen into glucose and release it into the bloodstream. The pancreas contains Islets of Langerhans, cells which produce the hormones. Beta cells produce insulin and alpha cells produce glucagon.
Insulin secreted by the beta cells of the pancreatic islets tends to lower the blood glucose. Insulin antagonises in various ways the cellular metabolic processes and the controlling influences of the hormones which tend to raise the blood glucose level. It lowers blood glucose mainly by promoting the transport of glucose from extracellular fluid into cells. Insulin also activates enzymes responsible for a variety of metabolic changes which glucose undergoes inside cells ( e.g., oxidation, deposition) as glycogen and conversion to fat or amino acids. Insulin antagonists also tend to raise the blood glucose level. For example cortisol and pituitary growth hormone reduce the uptake of glucose by tissues.