Tuesday, August 7, 2018

β-cells in pancreas

The islets of langerhans consist of insulin-releasing β-cells (65-90%) forming the core of the islet, glucagon-releasing alpha-cells (15-20%), somatostatin-producing delta-cells (3-10%), and pancreatic polypeptide-producing PP-cells (1%) are usually located on the surface.

Increased blood glucose after a meal is countered by the subsequent increased release of the hypoglycemic hormone insulin from the pancreatic β-cells.

The insulin gene is composed of four exons and two introns. the hormone’s precursor (preproinsulin), with 1150 Da, carries a signal peptide that directs the peptide chain to the interior of the endoplasmic reticulum (eR) and contains four peptides: N-terminal signal peptide, B chain, C peptide and A chain.

Insulin is secreted by the endocrine pancreatic β-cells upon an increase in blood glucose to lower the blood glucose level.

Glucose is the principal physiological insulin secretagogue and a potent regulator of β-cells activity. The increased blood glucose, usually occurring after a meal (postprandial), is sensed by the β-cells and glucose is taken up by glucose transporters.

Once inside, glucose is first converted to glucose-6-phosphate by glucokinase and then in the glycolysis to pyruvate, which enters the mitochondria.

Zinc plays an essential role in the regulation of pancreatic β-cells function, affecting important processes including pro-insulin biosynthesis, glucose-stimulated insulin secretion, and cell viability. Mutations in zinc efflux transport protein ZnT8 have been linked with both type 1 and type 2 diabetes.

Type 1 diabetes results from pancreatic β-cells degeneration and is characterized by lack of insulin production, while patients with Type 2 diabetes show a state of insulin resistance and usually relative insulin deficiency.
β-cells in pancreas
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