Pancreas is one of the largest digestive glands in the body, with both endocrine and exocrine functions. Islets are the cell populations interspersed among pancreatic acini, the number of which gradually increase from the head of the pancreas to the tail. Islet contains four different cells.
A cells: secreting glucagon;
B cells: smaller than A cells, secreting insulin, proinsulin and C peptide;
D cells: secreting somatostatin and vasoactive intestinal peptide;
F cells: secreting pancreatic polypeptide.
Insulin promotes glycogen synthesis, inhibits glycogen breakdown and gluconeogenesis, promotes the use of sugar and fat synthesis, inhibits lipolysis; promotes protein synthesis, inhibits protein decomposition; promotes the synthesis of DNA, RNA and adenosine triphosphate (ATP).
C-peptide (C-P) has no biological activity, is one of the indicators of pancreatic islet function.
The physiological role of proinsulin is similar to insulin, but has weaker action intensity than insulin.
Glucagon promotes decomposition to ensure the energy supply between two meals, promotes liver gluconeogenesis, increases blood glucose, promotes lipolysis, inhibits the secretion of gastric acid and pepsin, increases the secretion of bile and intestinal; stimulates the secretion of insulin, growth hormone, calcitonin and thyroxine.
Insulin antibodies can counteract insulin in the blood, delay the degradation of insulin and activate alexin.
Pancreatic polypeptide (PP) inhibit of gallbladder contraction, reduces bile output, inhibits pancreatic enzyme release, inhibit the secretion of motilin.