Human Anatomy Part 1 - K. A. Dyubenko, A. K. Kolomiysev, Yu. B. Chaykovsky 2002

Special Part
Endocrine glands (ductless glands), glandulae endocrinae (glandulae sine ductibus)
Organs combining endocrine and non-endocrine functions - Endocrine part of the pancreas

The Pancreas consists of exocrine and endocrine portions. The Endocrine Part accounts for 0.9–3.6% of the organ's mass and is represented by clusters of endocrine Cells (insulocytes) located within the lobules of the exocrine gland. These clusters, measuring 0.3 mm in diameter with a total weight of about 1 g, are known as the pancreatic islets of Langerhans (Fig. 347), first described by him in 1869.

The human pancreas contains approximately one million pancreatic islets (Jungqueira, 1980), which produce 2 mg of Insulin per day.

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Fig. 347. Duodenum, pancreas, and pancreatic islet (insula pancreatica) (diagram)

Pancreatic islets consist of four main Cell types. The predominant ones are B-cells, which make up 60–80% of all islet cells. They produce the hormone insulin, which enters the bloodstream and participates in regulating Blood glucose levels. Insufficient insulin production by B-cells leads to Diabetes Mellitus, a condition requiring the administration of exogenous insulin. About one-fifth of the pancreatic islet cells are A-cells, which serve as the source of the hormone Glucagon.

The pancreatic islets also contain gamma and delta cells, which produce the hormone gastrin. They account for about 5% of the total number of islet cells (Jungqueira, 1980).

Blood supply to the Endocrine portion of the pancreas. The pancreatic islets are supplied with blood via an arteriolar or capillary type (K. A. Dyubenko, 1968). In the arteriolar type of blood supply, an islet receives one or two dedicated afferent vessels branching from lobular or interlobular arterioles; these penetrate the islet parenchyma and break up into sinusoidal capillaries that form capillary glomeruli. In the capillary variant, the islet is supplied by capillaries originating from the exocrine portion of the pancreas.

Innervation of the endocrine portion of the pancreas. The innervation is derived from nerve fibers extending to the pancreas from the Vagus nerve, as well as the celiac and mesenteric plexuses. Nerve fibers penetrate the gland parenchyma, forming periacinar, periinsular, and perivascular plexuses containing numerous small ganglia. Individual ganglia contact the Cells of the pancreatic islets, forming the so-called neuroinsular complex (K. Kuristi, N. Fujita, 1975). According to some authors (E. Hagen, 1956), parasympathetic fibers terminate directly within the pancreatic islets. In addition to parasympathetic innervation, A- and B-cells receive sympathetic and adrenergic innervation (A. C. Esterhuizen, T. L. B. Spriggs, J. D. Lever, 1968).