Insulin is a kind of polypeptide. Insulin is a protein hormone secreted by pancreatic islet β cells stimulated by endogenous or exogenous substances, and insulin is synthesized in pancreatic islet β cells.
insulin consists of two peptide chains, A and B. The A chain of human insulin consists of 11 kinds of 21 amino acids, the B chain consists of 15 kinds of 3 amino acids and 16 kinds of 51 amino acids. Among them, sulfhydryl groups in the four cysteines A7(Cys)-B7(Cys) and A2(Cys)-B19(Cys) form two disulfide bonds, which connect the two chains A and B.
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Extended data:
Insulin secretion is mainly affected by the following factors:
1. Plasma glucose concentration is the most important factor affecting insulin secretion. After oral or intravenous injection of glucose, insulin release showed a two-phase reaction. In the early rapid phase, insulin in portal vein plasma reached the highest value within 2 minutes, and then decreased rapidly; In the slow phase, the plasma insulin level gradually increased after 1 minutes, which lasted for more than 1 hour.
2. After eating foods containing more protein and protein, the concentration of amino acids in blood increased, and insulin secretion also increased. Arginine, lysine, leucine and phenylalanine all have strong effects on stimulating insulin secretion.
3. The increase of gastrointestinal hormones after meals can promote insulin secretion. For example, gastrin, pancreatin, gastric inhibitory peptide and intestinal vasoactive peptide all stimulate insulin secretion.
4. Autonomic nerve function promotes insulin secretion when vagus nerve is excited; When sympathetic nerve is excited, it inhibits insulin secretion.
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