Exocrine Pancreatic Insufficiency

Exocrine Pancreas

Exocrine Pancreas Normal Structure

• The human pancreas, though anatomically a single organ, histologically and physiologically has 2 distinct parts the exocrine and endocrine parts.
• The endocrine part of the gland is dealt with in Chapter 27 while the exocrine gland is considered here. The whole of the pancreas, exocrine and endocrine, is embryologically derived from the foregut endoderm.

Exocrine Pancreas Anatomy The pancreas lies obliquely in the concavity of the duodenum as an elongated structure about 15 cm in length and 100 gm in weight. It is subdivided into 3 topographic zones:

1. The head lies in the concavity of the duodenum and the uncinate process projects from the head.
2. The body comprises the main part of the gland.
3. The tail is the thin, tapering part of the gland towards the hilum of the spleen.

Exocrine Pancreas Histology The exocrine pancreas constitutes 80 to 85% of the total gland, while the endocrine pancreas comprises the remaining part.

• The exocrine part is divided into rhomboid lobules separated by thin fibrous tissue septa containing blood vessels, lymphatics, nerves and ducts.
• Each lobule is composed of numerous cini. The acini are lined by pyramid-shaped columnar epithelial cells. These secretory epithelial cells have microvilli projecting into the lumen from their surface.
• The apical portions of these cells contain zymogen granules in their cytoplasm, while the basal region is deeply basophilic and free of zymogen granules.
• The zymogen granules are membrane-bound sacs which fuse with the plasma membrane and are then released into the lumina of the acini.
• The secretions are carried from the acini by fine ductal branches into the small ducts in the lobules and eventually into the main pancreatic duct.
• The main pancreatic duct is formed by the fusion of the ventral duct with the dorsal duct; the latter also called the duct of Wirsung, provides the main drainage for pancreatic secretions into the duodenum.
• The pancreatic secretions are delivered into the second part of the duodenum either by a combined opening of the pancreatic and bile ducts in the ampulla of Vater or less often both open separately into the duodenum.
• Occasionally, the proximal part of the dorsal duct persists as the duct of Santorini.

Exocrine Pancreas Functions The main functions of the exocrine pancreas are the alkaline secretion of digestive enzymes prominent among which are trypsin, chymotrypsin, elastase, amylase, lipase and phospholipase.