| | Re: What is insulin?
Insulin is a hormone that has profound effects on metabolism. Insulin causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle, and stopping use of fat as an energy source. When insulin is absent (or low), glucose is not taken up by body cells, and the body begins to use fat as an energy source, for example, by transfer of lipids from adipose tissue to the liver for mobilization as an energy source. As its level is a central metabolic control mechanism, its status is also used as a control signal to other body systems (such as amino acid uptake by body cells). In addition, it has several other anabolic effects throughout the body.
When control of insulin levels fails, diabetes mellitus will result. Consequently insulin is used medically to treat some forms of diabetes mellitus. Patients with Type 1 diabetes mellitus depend on external insulin (most commonly injected subcutaneously) for their survival because the hormone is no longer produced internally. Patients with Type 2 diabetes mellitus are insulin resistant, and because of such resistance, may suffer from a ''relative'' insulin deficiency. Some patients with Type 2 diabetes may eventually require insulin if other medications fail to control blood glucose levels adequately, though this is somewhat uncommon.
Insulin also influences other body functions, such as vascular compliance and cognition. Once insulin enters the human brain, it enhances learning and memory and in particular benefits verbal memory.