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Insulin is a peptide hormone containing two chains cross-linked by disulfide bridges. Insulin (/ ˈ ɪ n. sj ʊ. l ɪ n /, [5] [6] from Latin insula, 'island') is a peptide hormone produced by beta cells of the pancreatic islets encoded in humans by the insulin (INS) gene. It is the main anabolic hormone of the body. [7]
The effects of insulin vary depending on the tissue involved, e.g., insulin is most important in the uptake of glucose by muscle and adipose tissue. [ 2 ] This insulin signal transduction pathway is composed of trigger mechanisms (e.g., autophosphorylation mechanisms) that serve as signals throughout the cell.
Once insulin binds to the receptor, phosphorylation takes place and attaches to the beta-subunit, thus initiating the transduction process. A protein binds to the phosphorylated receptor protein, becoming phosphorylated as well.
The insulin receptor (IR) is a transmembrane receptor that is activated by insulin, IGF-I, IGF-II and belongs to the large class of receptor tyrosine kinase. [5] Metabolically, the insulin receptor plays a key role in the regulation of glucose homeostasis; a functional process that under degenerate conditions may result in a range of clinical manifestations including diabetes and cancer.
Increased insulin secretion leads to hyperinsulinemia, but blood glucose levels remain within their normal range due to the decreased efficacy of insulin signaling. [4] However, the beta cells can become overworked and exhausted from being overstimulated, leading to a 50% reduction in function along with a 40% decrease in beta-cell volume. [ 9 ]
Insulin was first used as a medication in Canada by Charles Best and Frederick Banting in 1922. [85] [86] This is a chronology of key milestones in the history of the medical use of insulin. For more details on the discovery, extraction, purification, clinical use, and synthesis of insulin, see Insulin
Diabetes mellitus type 1 is caused by insufficient or non-existent production of insulin, while type 2 is primarily due to a decreased response to insulin in the tissues of the body (insulin resistance). Both types of diabetes, if untreated, result in too much glucose remaining in the blood (hyperglycemia) and many of the same complications.
There are about 1 million islets distributed throughout the pancreas of a healthy adult human. While islets vary in size, the average diameter is about 0.2 mm. [5]:928 Each islet is separated from the surrounding pancreatic tissue by a thin, fibrous, connective tissue capsule which is continuous with the fibrous connective tissue that is interwoven throughout the rest of the pancreas.