What is Insulin?
Insulin is an anabolic peptide hormone secreted by pancreatic beta cells in response to rising glucose and other secretagogues. It is released into the portal circulation, where the liver extracts a substantial first-pass fraction, and it has a short plasma half-life of only a few minutes. Insulin promotes cellular glucose uptake, glycogen and lipid synthesis, and suppression of hepatic glucose output. It is co-secreted with C-peptide in equimolar amounts, but unlike C-peptide, exogenous insulin and significant hepatic clearance complicate the interpretation of measured insulin.