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Endocrine Part of the Pancreas

Pars endocrina pancreatis

For medical students2 min readUpdated 2026-10-10

The pancreas (pancreas) is a complex compound gland with mixed secretion. Its endocrine part is responsible for producing hormones that are released directly into the bloodstream and is represented by specialized morphological structures known as pancreatic islets.

Type of secretionMixed (has both exocrine and endocrine parts)

LocalizationScattered throughout the organ, with the highest concentration in the tail

HormonesInsulin and glucagon for carbohydrate metabolism regulation

Age-related changesMaximum quantity in early life, decreasing with age

General Characteristics and Embryonic Development

The pancreas is physiologically and anatomically divided into two functional components: the exocrine part (pars exocrina pancreatis) and the endocrine part (pars endocrina pancreatis).

The endocrine apparatus of the organ is represented by pancreatic islets (insulae pancreaticae), traditionally referred to in classic literature as the islets of Langerhans. Like all pancreatic tissue, these structures are derivatives of the endoderm. During embryogenesis, they develop directly from the glandular epithelium of the duodenum, gradually forming isolated endocrine clusters.

Morphology and Microscopic Structure

Visually, pancreatic islets stand out against the surrounding exocrine tissue due to their characteristic yellowish tint.

Main morphological characteristics of the islets:

Shape: predominantly oval or round formations.
Size: on average, an islet measures up to 0.3 mm, though individual larger specimens can reach 1 mm in diameter.
Histological structure: the core of the islet is formed by specialized epithelial cells. They are densely surrounded by connective tissue, within which a dense and branched network of sinusoidal venous capillaries is located. This rich blood supply is critical for the immediate transport of synthesized substances.

Topography and Functional Significance

Pancreatic islets are distributed unevenly. Although they are found throughout the entire thickness of the pancreas, their absolute majority and highest density are concentrated in the tail of the organ.

The main function of pancreatic islet cells is to produce key hormones—insulin and glucagon. Thanks to the sinusoidal capillaries, these hormones are secreted directly into the blood, bypassing excretory ducts. In the systemic circulation, they perform the vital task of regulating carbohydrate metabolism in the body.

It is worth noting the pronounced age-related dynamics of the endocrine apparatus: in early childhood, the number of pancreatic islets is relatively high, but as the organism matures and ages, their number gradually decreases.

Mnemonic

To remember the topography of the islets, use the mnemonic: 'Sweet Tail'. Carbohydrate metabolism (sweet) is regulated by islet hormones, the largest accumulation of which is located precisely in the tail of the pancreas.

Frequently asked questions

What cell types make up the pancreatic islets and what hormones do they produce?

Pancreatic islets contain several types of insular cells responsible for producing specific hormones:

A cells — produce glucagon.
B cells — produce insulin and amylin.
D cells — produce somatostatin.
D1 cells — produce vasoactive intestinal peptide (VIP).
PP cells (or F cells) — produce pancreatic polypeptide.

What is the histological structure of the exocrine part of the pancreas?

The exocrine part of the pancreas has a complex tubulo-alveolar structure. The parenchyma of the organ is divided by connective tissue interlobular septa (septa interlobares) that form lobules (lobi pancreatis).

Pancreatic acini (acini pancreatis) — the smallest structural elements consisting of glandular epithelium. They have an inhomogeneous staining: a dark basophilic periphery and a light oxyphilic center.
Excretory ducts — small ducts form within the lobules. Interlobular ducts are lined with single-layered epithelium and have a thick connective tissue sheath.

From which embryonic germ layer does the endocrine pancreas develop?

Pancreatic islets, like the entire organ, are endodermal derivatives and develop from the glandular epithelium of the duodenum.

Where in the pancreas is the highest concentration of the islets of Langerhans located?

The islets are located throughout the entire thickness of the organ, but their highest concentration is found in the tail of the pancreas.

How does the number of pancreatic islets change with age?

In early life, the number of islets is relatively higher. With age, their number in the pancreas gradually decreases.

Go deeper

Histological structure of epithelial cells in pancreatic islets
Mechanism of islet development from the duodenal epithelium
Hemodynamics in the sinusoidal venous capillaries of the islets
Role of insulin and glucagon in carbohydrate metabolism regulation