Exocrine Pancreas
Like the parotid gland, the exocrine pancreas contains acinar or tubuloacinar secretory units. The acinar units consists of a simple epithelium of pyramidal serous cells. The cells have a narrow apical surface and a broad basal surface. They present acidophilic zymogen granules in the apical cytoplasm and basophilic basal cytoplasm. These granules contain a variety of an inactive digestive enzymes.
In TEM, the basophilic cytoplasm of the pancreatic acinar cells appears to have an extensive array of rER and free ribosomes. This contributes to the high level of protein synthetic activity of the acinar cells. The apical cytoplasm appears to contain a well-developed Golgi apparatus, which involve in the concentration and packaging of the secretory products. Throughout the cell, small mitochondria are found concentrated among the rER cisternae. Acinar cells form an isolated lumen by being joined to one another by junctional complexes at their apical poles. They present small microvilli extending from the apical surface and into which the zymogen granules are released by exocytosis.
In TEM, the basophilic cytoplasm of the pancreatic acinar cells appears to have an extensive array of rER and free ribosomes. This contributes to the high level of protein synthetic activity of the acinar cells. The apical cytoplasm appears to contain a well-developed Golgi apparatus, which involve in the concentration and packaging of the secretory products. Throughout the cell, small mitochondria are found concentrated among the rER cisternae. Acinar cells form an isolated lumen by being joined to one another by junctional complexes at their apical poles. They present small microvilli extending from the apical surface and into which the zymogen granules are released by exocytosis.
Duct System of the Exocrine Pancreas
The intercalated duct, the initial duct that leads from the acinus, lies within the acinus. Centroacinar cells are the intercalated duct cells marked the beginning of the duct within the acinus. They are squamous cells, having flattened nuclei and attenuated cytoplasm lacking both ergastoplasm and secretory granules. Thus, they become lightly stained with eosin. The short intercalated ducts drain into intralobular collecting ducts, as there are no striated (secretory) ducts in the pancreas.
The intralobular collecting ducts form a complex, branching network that drains into the larger interlobular ducts. A low columnar epithelium line the interlobular ducts in which enteroendocrine cells and occasional goblet cells may be found. In turn, the interlobular ducts drain directly into the main pancreatic duct. This runs the length of the gland to open at the hepatopancreatic ampulla (of Vater) through which the common bile duct from the liver and gallbladder also enters the duodenum. The accessory pancreatic duct is a second large duct arising in the head of the pancreas.
The pancreas secretes about 1L of fluid per day, which is delivered directly to the duodenum. The fluid is composed of a small volume of protein-rich fluid secreted by the acinar cells and a large volume of fluid rich in sodium and bicarbonate secreted by the intercalated duct cells. The bicarbonate serves to neutralize and buffer the acidic chyme entering the duodenum from the stomach and to establish the optimal pH needed for the activity of the major pancreatic enzymes.
Cholecystokinin (CCK) and secretin hormones, produced by DNES cells in the small intestine, control the pancreatic exocrine secretion. In response to CCK, the acinar cells of the exocrine pancreas secrete the digestive enzymes (proenzymes). In addition, intercalated duct cells release the alkaline fluid in response to the secretin.
The intercalated duct, the initial duct that leads from the acinus, lies within the acinus. Centroacinar cells are the intercalated duct cells marked the beginning of the duct within the acinus. They are squamous cells, having flattened nuclei and attenuated cytoplasm lacking both ergastoplasm and secretory granules. Thus, they become lightly stained with eosin. The short intercalated ducts drain into intralobular collecting ducts, as there are no striated (secretory) ducts in the pancreas.
The intralobular collecting ducts form a complex, branching network that drains into the larger interlobular ducts. A low columnar epithelium line the interlobular ducts in which enteroendocrine cells and occasional goblet cells may be found. In turn, the interlobular ducts drain directly into the main pancreatic duct. This runs the length of the gland to open at the hepatopancreatic ampulla (of Vater) through which the common bile duct from the liver and gallbladder also enters the duodenum. The accessory pancreatic duct is a second large duct arising in the head of the pancreas.
The pancreas secretes about 1L of fluid per day, which is delivered directly to the duodenum. The fluid is composed of a small volume of protein-rich fluid secreted by the acinar cells and a large volume of fluid rich in sodium and bicarbonate secreted by the intercalated duct cells. The bicarbonate serves to neutralize and buffer the acidic chyme entering the duodenum from the stomach and to establish the optimal pH needed for the activity of the major pancreatic enzymes.
Cholecystokinin (CCK) and secretin hormones, produced by DNES cells in the small intestine, control the pancreatic exocrine secretion. In response to CCK, the acinar cells of the exocrine pancreas secrete the digestive enzymes (proenzymes). In addition, intercalated duct cells release the alkaline fluid in response to the secretin.
Histology Text: Major Salivary Glands - Liver - Gallbladder - Endocrine Pancreas
Histology Atlas - Histopathology - Histology Quiz
Histology Atlas - Histopathology - Histology Quiz