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Endocrine Pancreas

Q: What is the histological structure and blood supply of the islets of Langerhans?

Pancreatic islets (insulae pancreaticae, islets of Langerhans) are oval or round compact clusters of endocrine cells — insulocytes — located between the pancreatic acini. They poorly take up standard histological stains and therefore appear light against the background of the exocrine portion. The islets consist of several hundred or thousand insulocytes. Reticular fibers, fenestrated blood capillaries, and nerve fibers are located between the insulocytes. The islets are also described as structures surrounded by connective tissue with a dense network of venous sinusoidal capillaries. Between the cells, there are fenestrated capillaries with a pericapillary space — the site of primary hormone entry.

Insulae pancreaticae

For medical students2 min readUpdated 2026-10-10

The endocrine part of the pancreas is responsible for producing hormones that globally manage energy metabolism and locally control the function of the organ itself and the gastrointestinal tract. This system ensures a delicate balance between nutrient storage and expenditure.

Two groupsHormones are divided into regulators of metabolism and regulators of the gland itself and the GI tract.

InsulinLowers blood glucose levels, exerting a pronounced anabolic effect after a meal.

GlucagonRaises blood glucose levels by mobilizing tissue reserves between meals.

SomatostatinA universal inhibitor that suppresses the function of both the exocrine and endocrine parts.

Classification of Pancreatic Hormones

The hormonal profile of the organ can be divided into two major functional groups. The first group is responsible for systemic carbohydrate and lipid metabolism, adapting the body to food intake. The second group specializes in regulating the secretory activity of the pancreas itself, while also influencing the gastrointestinal tract and hemodynamics.

Regulation of Carbohydrate and Lipid Metabolism

Two classic antagonistic hormones are responsible for maintaining energy balance. Their secretion directly depends on the body's current energy demands.

Insulin. This is a key anabolic hormone that acts actively after a meal. Its main task is to facilitate the transport of nutrient substrates (glucose, amino acids, and fatty acids) from the bloodstream into tissues. Insulin triggers the synthesis of tissue reserves: it stimulates the formation of glycogen, proteins, and fats. A logical result of its action is a pronounced decrease in blood glucose concentration.
Glucagon. It has the opposite, catabolic effect and comes to the forefront between meals (in the fasting state). It stimulates the mobilization of stored carbohydrates and fats from tissues, returning them to the bloodstream. As a result, blood glucose concentration increases, providing organs with necessary energy.

Regulation of Pancreatic and GI Functions

This group of biologically active substances locally controls digestion, enzyme secretion, and vascular tone.

Somatostatin. Acts as a universal inhibitor. It is produced not only in the pancreas but also in the GI mucosa and the hypothalamus. The mechanism of its action consists of the total suppression of the production of other hormones and enzymes:
In the pituitary gland, it inhibits the secretion of growth hormone (GH).
In the pancreas, it suppresses the release of insulin and glucagon.
In the GI tract, it blocks the production of gastrin and secretin (furthermore, secretin normally stimulates the exocrine part of the gland).

Outcome: somatostatin inhibits the work of both parts of the pancreas — endocrine and exocrine.

Vasoactive Intestinal Polypeptide (VIP). Acts as a functional antagonist of somatostatin at the level of the pancreas itself. It actively stimulates the secretion of pancreatic juice and local hormones. In addition, VIP causes blood vessel dilation (vasodilation), leading to a systemic drop in blood pressure.

Pancreatic Polypeptide (PP). Its functional effect consists in the direct stimulation of digestive juice secretion — both pancreatic and gastric.

Mnemonic

Insulin — INvests (stores substances after a meal), Glucagon — Goes to blood (releases energy between meals), Somatostatin — Stop sign (halts all processes).

Frequently asked questions

What cell types make up the islets of Langerhans?

The islets of Langerhans comprise five main types of endocrine cells (insulocytes) with specific secretory activity.

A cells (Alpha cells) — located mainly at the periphery of the islets, contain dense granules, and produce glucagon.
B cells (Beta cells) — occupy the central part of the islets (60–70%), producing insulin.
D cells (Delta cells) — lie at the periphery of the islets, their granules are evenly filled, and they secrete somatostatin.
D1 cells — usually located at the periphery, producing vasoactive intestinal peptide (VIP).
PP cells — located at the periphery of the islets, synthesizing pancreatic polypeptide.

Which cells of the endocrine pancreas secrete insulin?

Insulin is secreted by beta cells (B cells) of the pancreatic islets. They account for the majority of all endocrine cells in the pancreas and are located predominantly in the center of the islets.

B cells — oval or polygonal endocrinocytes with a well-developed synthetic apparatus. Their secretory granules have a central dense irregular part surrounded by a wide light halo. Inside the granules are crystalloids, which represent a complex of insulin molecules with zinc.

What is the histological structure and blood supply of the islets of Langerhans?

Pancreatic islets (insulae pancreaticae, islets of Langerhans) are oval or round compact clusters of endocrine cells — insulocytes — located between the pancreatic acini. They poorly take up standard histological stains and therefore appear light against the background of the exocrine portion.

The islets consist of several hundred or thousand insulocytes. Reticular fibers, fenestrated blood capillaries, and nerve fibers are located between the insulocytes. The islets are also described as structures surrounded by connective tissue with a dense network of venous sinusoidal capillaries. Between the cells, there are fenestrated capillaries with a pericapillary space — the site of primary hormone entry.

Which pancreatic hormones are functional antagonists?

In the regulation of carbohydrate metabolism, these are insulin (lowers glucose) and glucagon (raises glucose). In regulating the function of the gland itself, they are somatostatin (inhibitor) and vasoactive intestinal polypeptide (stimulator).

Where else, besides the pancreas, is somatostatin produced?

Somatostatin is also synthesized in the hypothalamus, where it inhibits GH production in the pituitary gland, and in the mucosa of the gastrointestinal tract.

How does vasoactive intestinal polypeptide (VIP) affect hemodynamics?

VIP causes blood vessel dilation (vasodilation). As a result of this effect, blood pressure decreases.

Go deeper

Mechanisms of glucose, amino acid, and fatty acid transport into tissues under the action of insulin
Processes of glycogen, protein, and fat synthesis (anabolic effects)
Pathways of carbohydrate and lipid mobilization under the influence of glucagon
Role of secretin in stimulating the exocrine portion of the pancreas
Interrelation of somatostatin with growth hormone (GH) production in the pituitary gland