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Histology Of Pancreas – Zoology Notes – For W.B.C.S. Examination.
The pancreas is both an exocrine accessory digestive organ and a hormone secreting endocrine gland. The bulk of the pancreatic tissue is formed by the exocrine component, which consists of many serous pancreatic acini cells. These acini synthesize and secrete a variety of enzymes essential to successfully “rest and digest”.Continue Reading Histology Of Pancreas – Zoology Notes – For W.B.C.S. Examination.
But don’t let the nirvana after a great meal fool you. While “resting” sounds really nice, the “digesting” part involves some heavy machinery. This is where the pancreas comes at play. Every day, this organ is maneuvering dangerous digestive enzymes, and one little slip up could cause its own self destruction. Talk about occupational hazard!
The endocrine component is a much smaller, but equally important, portion of the pancreas. It is composed of pancreatic islets, which appear as islands of cells dispersed between the pancreatic acini. These islet cells produce and secrete hormones that regulate glucose, lipid and protein metabolism.
| Exocrine pancreas | Secretory units: pancreatic acini Cells: acinar cells, centroacinar cells Products: peptidases, lipases, amylolytic enzymes, nucleolytic enzymes |
| Endocrine pancreas | Secretory units: islets of Langerhans Cells: A (alpha), B (beta), D (delta), PP (pancreatic polypeptide) cells Products: insulin, glucagon, somatostatin |
| Distinguishing histological features | Presence of islets of Langerhans Beginning of intercalated ducts within acini |
| Clinical information | Diabetes mellitus |
The pancreas is a large, mixed gland composed of five parts: the head, uncinate process, neck, body and tail. The location of the pancreas is mostly retroperitoneal, except for the tail. This organ extends from the C-shaped curve of the duodenum, passes behind the stomach and finishes at the hilum of the spleen. Several pancreatic ducts extend throughout the pancreas, emptying the pancreatic contents inside the duodenum.
The pancreas is covered by a thin capsule made of loose connective tissue. The parenchyma consists of pancreatic acini and sparsely scattered pancreatic islets surrounded by stroma of loose connective tissue. Interlobular connective tissue septa project from the capsule into the pancreatic parenchyma, organising it into lobules. The interlobular septa house the interlobular ducts, blood vessels, nerves, and lamellar (Pacinian) corpuscles, which are special types of sensory receptors.
The exocrine component of the pancreas makes up about 98% of the pancreatic tissue. It is comprised of densely packed serous acinar (tubuloacinar) glands. These glands are called pancreatic acini, which represent the secretory units of the pancreas. They are formed out of simple epithelium. Each pancreatic acinus consists of pyramidal-shaped acinar cells, which have a broad basal portion and a narrow apical surface that surround a small central lumen.
These acinar cells are serous secretory cells that produce digestive enzymes. Their secretory function is attested by the presence of abundant rough endoplasmic reticulum and Golgi apparatus. Seen under a microscope, their basal cytoplasm is largely basophilic, with distinct acidophilic zymogen granules in their apical poles. Zymogen granules are large secretory organelles in which acinar cells store their inactive enzymes, called zymogens or proenzymes. Upon stimulation, the zymogens are activated and the acinar cells release their secretions by way of exocytosis. During exocytosis, the granules merge with the cell membrane and expel their contents into the lumen of the acinus.
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