General characteristics and embryonic development
Physiologically and anatomically, the pancreas is 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 as the islets of Langerhans in classical literature. 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, the pancreatic islets stand out against the surrounding exocrine tissue of the organ by their characteristic yellowish hue.
Main morphological characteristics of the islets:
- Shape: predominantly oval or rounded formations.
- Dimensions: on average, an islet measures up to 0.3 mm, though individual largest specimens may reach 1 mm in diameter.
- Histological structure: the basis of the islet is formed by specialized epithelial cells. They are densely surrounded by connective tissue, within which a dense and branched network of venous sinusoidal capillaries is located. Such abundant blood supply is critical for the immediate transport of synthesized substances.
Topography and functional significance
Pancreatic islets are unevenly distributed. Although they are found throughout the thickness of the pancreas, their absolute majority and highest density are concentrated in the tail of the organ.
The main function of the 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 the excretory ducts. In the systemic circulation, they perform a crucial task: 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 large, but as the organism matures and ages, their number gradually decreases.
Briefly: answers to topical questions
What cell types are part of the pancreatic islets and what hormones are they responsible for producing?
The pancreatic islets include several types of insulocytes 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 tubuloacinar structure. The parenchyma of the organ is divided by connective tissue interlobular septa (septa interlobares), which form lobules (lobi pancreatis).
- Pancreatic acini (acini pancreatis)—the smallest structural elements consisting of glandular epithelium. They have a heterogeneous staining: a dark basophilic periphery and a light oxyphilic center.
- Excretory ducts—small ducts form inside the lobules. Interlobular ducts are lined with single-layered epithelium and have a thick connective tissue sheath.
To remember the topography of the islets, use the mnemonic: "Sweet tail." Carbohydrate metabolism (sweet) is regulated by the islet hormones, the largest cluster of which is located precisely in the tail of the pancreas.
Class and exam questions
From which embryonic germ layer does the endocrine portion of the pancreas develop?
Pancreatic islets, like the organ as a whole, are derivatives of the endoderm and develop from the glandular epithelium of the duodenum.
Where in the pancreas is the largest number of islets of Langerhans localized?
The islets are located throughout the thickness of the organ, but their greatest number is concentrated in the tail of the pancreas.
How does the number of pancreatic islets change with age?
At an early age, the number of islets is relatively greater. With age, their number in the pancreas gradually decreases.
What else to study on this topic
- Histological structure of the epithelial cells of the pancreatic islets
- Mechanism of islet development from the duodenal epithelium
- Hemodynamics in the venous sinusoidal capillaries of the islets
- The role of insulin and glucagon in regulating carbohydrate metabolism
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