Human Anatomy and Physiology - N. I. Fedyukovich 2003

Glands of Internal Secretion
The Endocrine Part of the Pancreas

The Pancreas consists of an exocrine and an endocrine portion. The Endocrine Part is represented by clusters of epithelial Cells (Islets of Langerhans) separated from the exocrine tissue by delicate Connective Tissue septa. The vast majority of the islets are concentrated in the tail of the pancreas. Pancreatic islets typically range from 0.1 to 0.3 mm in diameter, and their total mass does not exceed 1/100 of the pancreatic weight.

The pancreatic islets contain two MAIN TYPES OF glandular cells. The Insulin-producing cells are designated as beta (or β) cells, while the Glucagon-secreting cells are known as alpha (or α) cells.

Insulin is a protein hormone with a Molecular Weight of approximately 6,000 Da. It is generated from proinsulin through the action of proteases. The conversion of proinsulin into the active hormone insulin takes place within the beta cells. Insulin secretion is regulated by the sympathetic and parasympathetic nervous systems, as well as by several Polypeptides produced in the gastrointestinal tract.

Glucagon is a polypeptide composed of a single chain with a molecular weight of approximately 3,500 Da. It can also be produced in the intestine in the form of enteroglucagon.

The regulation of glucagon secretion is mediated by hypothalamic glucose receptors that detect drops in Blood glucose levels. This regulatory pathway also incorporates Growth Hormone, Somatostatin, enteroglucagon, and the sympathetic Nervous system.

Islet Hormones exert a profound influence on metabolic processes. Insulin is an anabolic hormone with a broad spectrum of activity. Its primary role is to enhance the synthesis of CARBOHYDRATES, Lipids, and Proteins. It stimulates glucose METABOLISM, increases glucose permeability in myocardial and Skeletal Muscle cells, and thereby facilitates a greater influx of glucose into the cells. Insulin lowers blood glucose levels, promotes hepatic Glycogen synthesis, and regulates Lipid Metabolism.

The primary effect of glucagon is linked to The stimulation of hepatic metabolic pathways, The breakdown of glycogen into glucose, and its release into the bloodstream. Glucagon acts as a synergist to adrenaline. Deviations of blood glucose from normal levels result in either hypoglycemia or hyperglycemia. An insulin deficiency or an alteration in its biological activity leads to a sharp increase in blood glucose, which can trigger Diabetes Mellitus accompanied by typical clinical symptoms. Conversely, elevated blood glucose levels driven by glucagon excess lead to hypoglycemic states.