Answer
The main hormone that regulates absorptive state conditions is insulin-- secreted by the beta cells of the pancreas (Islets of Langerhans). Insulin is secreted as soon as blood levels of glucose and of amino acids (aa's) rise. It regulates (increases) the rate of glucose uptake by all cells except, neurons, erythrocytes (RBC) and kidney cells (hepatocytes). In addition, insulin regulates glucose oxidation, glycogenesis, and lipogenesis; it also and suppresses gluconeogenesis. Furthermore, insulin promotes amino acid uptake and protein synthesis, and serves as an adiposity indicator for the brain.
The main hormonal antagonist of insulin is glucagon--high serum levels of aa's stimulate the release of glucagon as well as insulin. Consequently, in conditions of low serum levels of glucose and high dietary protein intake, the amino acid release of glucagon protects against the depletion of plasma glucose and the development of hypoglycemia.
Work Step by Step
Gastrin, secretin, cholecystokinin (CCK), and glucose-independent insulinotropic peptide (GIP) are also hormones that stimulate the secretion of insulin. On the other hand, insulin is also antagonized by the catecholamines, growth hormone, and cortisol-- in addition to glucagon.
