Insulin is a hormone which regulates blood glucose concentration. Insulin binds to insulin receptors on the surface of cells in insulin-dependent tissues and this triggers an intracellular signalling cascade which leads to altered gene expression. One effect of this signalling cascade is the increased translocation of glucose transporters from vesicles to the surface of cells, such as GLUT4 in muscle tissue. This promotes the uptake of glucose into cells, providing the cell with glucose for energy production via various metabolic pathways, and reducing glucose concentration in the blood.
Blood glucose levels must be maintained at fairly constant levels, in order to ensure there is a steady supply of glucose to tissues at all times. High glucose levels can cause inflammation and tissue damage, whilst low glucose levels causes cells to adopt a “starved” state where they lack their normal form of energy. Whilst some tissues can yield energy from alternative sources such as ketone bodies from triglyceride stores, the brain, which is heavily dependent on glucose for energy production, is very sensitive to low blood glucose concentration, which if prolonged can lead to confusion, coma and even death.
Type 1 diabetes cause a deficiency of insulin production, as it is an autoimmune disease characterised by the destruction of pancreatic beta cells which produce insulin. Type 2 diabetes is characterised by tissue insensitivity to insulin, although insulin may be produced at normal, or even increased amounts. With time however, patients with type 2 diabetes may develop type 1 diabetes if the pancreatic beta cells “burnout” from excessive insulin production.
For a brief flowchart showing the effects of insulin deficiency, please see below.