pancreas - Pancreas: Gross Anatomy The pancreas and liver...

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Pancreas: Gross Anatomy ? The pancreas and liver are the two large, extramural glands of the digestive system. ? The pancreas is a elongated organ, light tan or pinkish in colour, that lies in close proximity to the duodenum and is composed of a head, body, and tail. ? It is covered with a very thin connective tissue capsule which extends inward as septa, partitioning the gland into lobules. ? The pancreas, the smaller of the two glands, is a compound acinar gland, which weighs 60-100 g and is 10-15 cm long. ? The pancreas is composed of a larger exocrine portion and a smaller endocrine portion. ? The exocrine pancreas makes pancreatic juice, a digestive fluid collected by ducts and emptied into the duodenum where it acts on proteins, carbohydrates, and fats. ? The endocrine pancreas, consisting of the pancreatic islets (islands of Langerhans), makes insulin and glucagon, two hormones that are secreted into the blood stream. Pancreas: Microscopic Anatomy ? Pancreatic exocrine cells are arranged in grape-like clusters called acini (a single one is an acinus). ? The exocrine cells themselves are packed with membrane-bound secretory granules which contain digestive enzymes that are exocytosed into the lumen of the acinus. ? From there these secretions flow into larger and larger, intralobular ducts, which eventually coalesce into the main pancreatic duct which drains directly into the duodenum. ? The lumen of an acinus communicates directly with intralobular ducts, which coalesce into interlobular ducts and then into the major pancreatic duct. ? Epithelial cells of the intralobular ducts actually project "back" into the lumen of the acinus, where they are called centroacinar cells. Pancreas: Exocrine Secretions ? Pancreatic juice is composed of two secretory products critical to proper digestion: digestive enzymes and bicarbonate. ? The enzymes are synthesised and secreted from the exocrine acinar cells, whereas bicarbonate is secreted from the epithelial cells lining small pancreatic ducts. ? The pancreas secretes a magnificent battery of digestive enzymes that collectively have the capacity to reduce virtually all digestible macromolecules into forms that are capable of, or nearly capable of being absorbed. Three major groups of enzymes are critical to efficient digestion: 1. Proteases 2. Pancreatic lipase 3. Amylase ? Bicarbonate and water pancreatic secretion ? Epithelial cells in pancreatic ducts are the source of the bicarbonate and water secreted by the pancreas. ? Bicarbonate is a base and critical to neutralising the acid coming into the small intestine from the stomach. ? The mechanism underlying bicarbonate secretion is essentially the same as for
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acid secretion parietal cells and is dependent on the enzyme carbonic anhydrase. ? In pancreatic duct cells, the bicarbonate is secreted into the lumen of the duct
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pancreas - Pancreas: Gross Anatomy The pancreas and liver...

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