198 The Pancreas

The pancreas is an elongated retroperitoneal gland in the upperabdomenthathasbothanexocrineandanendocrine component. The pancreas is divided into three parts: the head, the body, and the tail. The head lies in the C-shaped region of the duodenum, while the body and tail extend fromtheC-loopoftheduodenumacrossthemidlineofthe body toward the spleen. Pancreatic secretion empties through the pancreatic duct which merges with the commonbileductsintotheduodenumviatheampullaofVater. In this chapter, the embryology, histology, ultrastructure, and development of the functions of the pancreas have been reviewed. In addition, the physiology of the pancreas, congenital diseases of the exocrine pancreas, and the evaluation of pancreatic function will be discussed. A detailed review of acute and chronic pancreatitis will also be provided. Embryology By the fifth week of gestation, the pancreas arises as two outpouchings from the junction of the foregut and midgut. The large dorsal bud enlarges rapidly and contributes to most of the pancreas. The small ventral bud contributes to the uncinate process and the inferior part of the head of the pancreas. The ventral bud, connected to the bile duct, rotates with the duodenum and fuses with the dorsal bud. By the seventh week of gestation, as the two buds join, the ventral duct fuses with the dorsal duct to form the main pancreatic duct (duct of Wirsung). This duct communicates with the common bile duct before entering the duodenumvia the ampulla of Vater. The proximal portion of the dorsal duct forms the accessory duct of Santorini, which opens separately above the main papilla. Developmental deviation from these steps may result in clinically significant anomalies as will be discussed later. The pancreatic acini and the islets of Langerhans start developing during the third month of gestation. Histology and Ultrastructure