The insulin pancreas apparatus consists of beta cells, which are located mainly in the center of the so-called islets of Langerhans. These islands occupy about 2% of the total pancreatic volume and are responsible for the endocrine function of the organ. In addition to beta cells, they also contain alpha, delta, and PP cells that also secrete hormones.
Beta cells make up about 80% of all cells in the islets, and can also be in small numbers in other parts of the pancreas. The shape of them is round or oval, sometimes with small processes. The core is large enough. The average diameter of one cell is 100 μm.
The main function of the insulin apparatus is to maintain normal blood glucose levels, which is due to:
- supporting basal insulin levels in the blood;
- rapid release of ready-made insulin from granules or activation of its synthesis with an increase in glucose level.
A hormone insulin is a protein molecule formed from two polypeptide chains connected by disulfide bonds. The biosynthesis of this hormone in the insulin apparatus of the pancreas takes about 1 hour and includes the following steps:
- formation of preproinsulin in the endoplasmic reticulum( ER);
- cleavage of preproinsulin as it passes through the ER membrane with microsomal proteases to proinsulin;
- transport and the accumulation of proinsulin in the Golgi apparatus;
- isolation of proinsulin from the Golgi apparatus into secretory granules;
- cleavage under the action of special proteolytic enzymes of proinsulin on insulin and C-peptide.
The hormone accumulates in the secretory granules, forming complexes with zinc and oligomers of different composition. When the signal( increase in glucose level) is received, rapid secretion of insulin into the blood takes place. Also, this process is influenced by some other hormones: glucagon, cortisol, adrenaline, secretin, etc.
Inhibition of the insulin apparatus of the pancreas
The oppression of the insulin apparatus leads to a gradual decrease in hormone production, increased glucose level and, ultimately, diabetes mellitus.
The main cause of pathological changes in the operation of beta cells of the pancreas in insulin-dependent diabetes of the first type is their death, which is due to an autoimmune process in the body. As a result of a viral disease( rubella, influenza, hepatitis, etc.), the immune system fails, and as a result, it begins to produce antibodies to beta cells, which leads to a gradual decrease in their number.
In type 2 diabetes, which is caused by the immunity of tissues to the hormone, oppression of the insulin apparatus is due to the production of large amounts of insulin. This eventually becomes the cause of the depletion of beta cells and the extinction of their function.