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The pancreas is a gland with both exocrine and endocrine functions. The exocrine pancreas contains acini, which secrete pancreatic juice into the duodenum through the pancreatic ducts (Figure 15–1). Pancreatic juice contains a number of enzymes, some of which are initially secreted as zymogens in an inactive form. Once activated, these enzymes help digest food and prepare it for absorption in the intestine. Disorders interfering with normal pancreatic enzyme activity (pancreatic insufficiency) cause fat maldigestion and steatorrhea (fatty stools). Pathology of the exocrine pancreas results from inflammation (acute pancreatitis, chronic pancreatitis), neoplasm (ductal adenocarcinoma, neuroendocrine tumors, other pancreatic neoplasms), or duct obstruction by stones or abnormally viscid mucus (cystic fibrosis).
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The endocrine pancreas is composed of the islets of Langerhans. The islets are distributed throughout the pancreas and contain several different hormone-producing cells. The islet cells manufacture hormones such as insulin that are important in nutrient absorption, storage, and metabolism. Dysfunction of the endocrine pancreas may cause diabetes mellitus (see Chapter 18).
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Exocrine and endocrine pancreatic dysfunction may occur together in some patients.
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NORMAL STRUCTURE & FUNCTION OF THE EXOCRINE PANCREAS
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The pancreas is a solid organ that lies transversely in the retroperitoneum deep within the epigastrium. It is firmly fixed by fibrous attachments anterior to the suprarenal aorta and the first and second lumbar vertebrae. Thus, the pain of acute or chronic pancreatitis is situated deep in the epigastric region and frequently radiates to the back.
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The normal pancreas is about 15 cm long and weighs less than 110 g. The organ is covered by a thin capsule of connective tissue that sends septa into it, separating it into lobules. The pancreas can be divided into four parts: the head, including the uncinate process; neck; body; and tail. The head is the thickest part of the gland (2–4 cm) and lies in the “C-loop” or curved space between the first, second, and third portions of the duodenum. The uncinate process is the portion of the head that extends dorsally and to the left, behind the superior mesenteric vessels. The neck connects the head and body and sits immediately ventral to the superior mesenteric vessels. The body is situated transversely in the retroperitoneal space, bordered superiorly by the splenic artery and dorsally by the splenic vein. The tail of the pancreas is less fixed in the retroperitoneum and extends toward, and often immediately adjacent to, the hilum of the spleen.
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Embryologically, the pancreas develops as two separate endodermal buds from the developing foregut. These separate dorsal and ventral elements of the primordial pancreas initially develop opposite each other but, with rotation of the primitive gut, end up fusing together toward the ...