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, and also affects the gastrointestinal tract and hemodynamics.
Regulation of carbohydrate and lipid metabolism
Two classic antagonist hormones are responsible for maintaining energy balance. Their secretion directly depends on the body's current energy needs.
- 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 work 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, the concentration of glucose in the blood rises, providing organs with the necessary energy.
Regulation of pancreatic and GI functions
This group of biologically active substances locally controls digestion, enzyme release, 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 in the total suppression of the production of other hormones and enzymes:
- In the pituitary gland, it inhibits the secretion of growth hormone (somatotropin/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).
Summary: somatostatin inhibits the function 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 release 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 is the direct stimulation of digestive juice secretion—both pancreatic and gastric.
Briefly: answers to topical questions
What cell types make up the islets of Langerhans?
The islets of Langerhans consist of 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%), and produce 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, produce vasoactive intestinal peptide (VIP).
- PP-cells — located at the periphery of the islets, synthesize 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 an irregular dense central core surrounded by a wide clear halo. Inside the granules are crystalloids, which are 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 rounded compact clusters of endocrine cells (insulocytes) located between the acini of the pancreas. They stain poorly with standard histological stains and therefore appear pale 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. There are fenestrated capillaries between the cells with a pericapillary space—the site of primary hormone release.
Insulin — INvests (stores substances after a meal), Glucagon — Goes into the blood (releases energy between meals), Somatostatin — Stop valve (inhibits all processes).
Class and exam questions
Which pancreatic hormones are functional antagonists?
In the regulation of carbohydrate metabolism, these are insulin (lowers glucose) and glucagon (raises glucose). In the regulation of gland functions, 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 gastrointestinal mucosa.
How does vasoactive intestinal polypeptide (VIP) affect hemodynamics?
VIP causes blood vessel dilation (vasodilation). This effect results in a drop in blood pressure.
What else to study on this topic
- 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
- The role of secretin in stimulating the exocrine pancreas
- The relationship between somatostatin and growth hormone (GH) production in the pituitary gland
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