Pancreatic Pathology Online
Anatomy of Normal Pancreas
The pancreas is a mixed exocrine-endocrine gland that extends transversely in the upper abdomen and is cradled between the loop of the duodenum and hilum of the spleen.
It is retroperitoneal, behind the lesser omental sac and the stomach, a location that renders it largely inaccessible to physical examination and other modalities of direct clinical assessment.
The adult pancreas is 10 to 15 cm long and weighs from 60 to 150 gm.
It is divided into three subdivisions :
- The head, which lies in the concavity of the duodenum and extends to the superior mesenteric vessels immediately behind the organ;
- The body, which includes most of the gland; and
- A tapered tail, which ends at the hilum of the spleen.
The secretions of the exocrine pancreas drain via the duct of Wirsung, which begins by the convergence of several small ducts in the tail and extends into the head, collecting secretions from ductal tributaries along the way.
It then turns downward and backward, where it empties into the duodenum at the ampulla of Vater.
Occasionally, in addition to the major duct, an accessory duct of Santorini represents the duct of the embryonic ventral pancreas.
The major pancreatic duct may enter the duodenum directly or, more commonly, drain into the common bile duct immediately proximal to the ampulla of Vater.
The common channel that carries bile and pancreatic secretions is invested with a circular complex of smooth muscle fibers, which condense as they pass through the duodenal wall into the sphincter of Oddi.
Exocrine tissue, comprising 80 to 85% of the pancreas, consists of secretory cells organized in acini that connect with ductules.
These in turn merge into small ducts that empty into medium and large ducts, and finally form the main pancreatic duct.
Acinar cells synthesize a wide range of digestive enzymes, which are secreted into the intestine following both neural and hormonal stimulation.
Stimulation of the vagus nerves increases the flow of pancreatic juice.
Amino acids and a duodenal - jejunal pH of less than 3 trigger the release of the polypeptide hormone cholecystokinin, and antral distension stimulates that of secretin.
Cholecystokinin and secretin bind to surface receptors on acinar and duct cells, respectively, stimulating the secretion of digestive enzymes from acinar cells and of bicarbonate ions and water from the duct cells.
Bicarbonate ions serve to neutralize the highly acidic gastric chyle in the intestine and to achieve an optimum pH for the function of pancreatic digestive enzymes.
The daily secretion of about 1.5 to 2 liters of pancreatic juice attests to the remarkable synthetic and secretory capacity of acinar cells and the transport of ions and water by ductal cells.
The endocrine pancreas consists of cells organized into islets that are distributed throughout the organ.
These endocrine islets comprise only about 2% of the total pancreas.
Islets contain several cell types, each of which synthesizes one or more hormones, including insulin and glucagons, among others.
Following the proper stimulus the hormones are secreted directly into the blood.
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