Hormone production Sample Clauses

Hormone production. Insulin is a hormone produced by the β-cells of the Islets of Langerhans in the pancreas. At birth about 3x10-5 islets are present, increasing to 1x10-6 islets during the first years of life. The islets contain various cell types which each produce different hormones. The β-cell produces insulin. Other important hormones are somatostatin, produced in the δ-cell, and glucagon, produced in the α-cell. The latter counteracts the effect of insulin in many ways. The β-cell is situated central in the islet of Langerhans whereas the other cells are located peripherally. ½ The human insulin gene is located on the short arm of chromosome 11. Via DNA/RNA re- synthesis, a precursor molecule known as pre-pro-insulin (98 amino acids, molecular weight [MW] 11.500) is produced in the endoplasmatic reticulum of the pancreatic β-cells. It is cleaved to proinsulin (86 amino acids, MW approximately 9000) directly after the molecule has left the ribosome. The proinsulin is transported to the Golgi apparatus, where packaging into clathrin-coated secretory granules takes place. Maturation of the secretory granule is associated with the loss of the clathrin coating. In addition, the proinsulin is converted into insulin and C-peptide (MW 3000) by proteolytic cleavage at two sites. Normal granules shed insulin and C-peptide in equimolar amounts, along with some proinsulin and so-called split- products (only partially cleaved proinsulin). Insulin (MW 5808) itself consists of an A-chain of 21 amino acids and a B-chain of 30 amino acids, which are connected by two disulfide bonds. The secreted insulin first passes the liver where a proportion of insulin is cleared via a receptor-mediated process after exerting its action59-61 The proportion of insulin cleared during first-pass through the liver has been estimated to be about 50% in dogs60 and approxi- mately 40 to 80% in humans62-65. The plasma half-life time (t ) of insulin is only 5-10 minutes. C-peptide, the 31 amino acid residue, has no known biological function. Since C-peptide is produced in equimolar amounts with insulin it can be used as a marker for insulin secretory capacity, because it is not cleared by the liver but by the kidney and has a longer t½ than insulin66,67.