Pancreatic disease
Anatomy and Physiology
Embryology • The pancreas arises in the 4th week of fetal life • Dorsal and ventral pancreatic buds • Only the caudal portion of the head and the uncinate process are derived from the ventral pancreas [1] Klein SD, Affronti JP. Pancreas divisum, an evidence-based review: part I, pathophysiology. Gastrointest Endosc. 2004;60(3):419-425. doi:10.1016/s0016-5107(04)01815-2 [2] Illustrations from The Netter Collection, Volume 3, Part 3. Illustrations by Frank H. Netter, MD
Anatomy • Lies within the retroperitoneum in the upper abdomen • Be divided into 4 portions—head, neck, body, and tail • The head of the pancreas is intimately adherent to the medial portion of the duodenum and lies in front of the inferior vena cava and superior mesenteric vessels. The stomach and the first portion of the duodenum lie partly in front of the pancreas. The common bile duct passes through a posterior groove in the head of the pancreas adjacent to the duodenum. [3] Atlas of human anatomy, Frank H. Netter, MD
• The blood supply of the pancreas is derived from branches of the celiac and superior mesenteric. The superior pancreaticoduodenal artery arises from the gastroduodenal artery, and eventually meets the inferior pancreaticoduodenal artery, a branch of the superior mesenteric artery, to form an arcade. The splenic artery provides tributaries that supply the body and tail of the pancreas. The main branches are termed the dorsal pancreatic, pancreatica magna, and caudal pancreatic arteries. The venous supply of the gland parallels the arterial supply. Lymphatic drainage is into the peripancreatic nodes located along the veins. • The innervation of the pancreas is derived from the vagal and splanchnic nerves. The visceral afferent fibers from the pancreas also travel in the vagal and splanchnic nerves, but those that mediate pain are confined to the latter
The main pancreatic duct runs along the gland from the tail to the head, before entering the duodenum, where it joins the common bile duct at the ampulla of Vater. The accessory pancreatic duct enters the duodenum at 2~2.5cm proximal to the ampulla of Vater. The ampulla of Vater is often located behind the inner wall of the middle of the second segment of the duodenum, about 7~10cm from the pylorus. It is the junction of the bile duct, pancreatic duct and digestive tract, and has important functions. [4] From Lehman, Feldman’s GastroAtlas Online. [4]
Physiology——Exocrine Function The external secretion of the pancreas consists of a clear, alkaline (pH 7.0-8.3) solution of 1-2 L/d containing digestive enzymes. The water and electrolyte secretion is formed by the centroacinar and intercalated duct cells principally in response to secretin stimulation. Pancreatic enzymes are synthesized, stored (as zymogen granules), and released by the acinar cells of the gland, principally in response to cholecystokinin and vagal stimulation. Turnover of protein in the pancreas exceeds that of any other organ in the body. Intravenously injected amino acids are incorporated into enzyme protein and may appear in the pancreatic juice within 1 hour. Three mechanisms prevent autodigestion of the pancreas by its proteolytic enzymes: (1) The enzymes are stored in acinar cells as zymogen granules, where they are separated from other cell proteins. (2) The enzymes are secreted in an inactive form. (3) Inhibitors of proteolytic enzymes are present in pancreatic juice and pancreatic tissue
In the non-digested period, pancreatic juice is secreted little or no. After eating, pancreatic juice begins to secrete. Therefore, food is a natural factor that stimulates the secretion of pancreatic juice. When eating, pancreatic juice is controlled by nerves and body fluids, but it is mainly controlled by body fluids. Pancreatic juice is mainly secreted and regulated by the stimulation of secretin, cholecystokinin (CCK) and the vagal nerve. Physiology——Exocrine Function
Physiology——Endocrine Function The function of the endocrine pancreas is to facilitate storage of foodstuffs by release of insulin after a meal and to provide a mechanism for their mobilization by release of glucagon during periods of fasting. Insulin and glucagon, as well as pancreatic polypeptide and somatostatin, are produced by the islets of Langerhans. cell hormone Endocrine tumors % （cell） α insulin Insulinoma 20% β Glucagon Glucagonoma 70% δ Somatostatin Somatostatinoma 5% G Gastrin Gastrinoma（ZES） Low D2 VIP VIPoma/WDHA Low Table Various pancreatic endocrine hormones and tumors
Annular Pancreas Annular pancreas is a rare congenital condition in which a ring of pancreatic tissue from the head of the pancreas surrounds the descending duodenum. The abnormality usually presents in infancy as duodenal obstruction with postprandial vomiting. There is bile in the vomitus if the constriction is distal to the entrance of the common bile duct. X-rays show a dilated stomach and proximal duodenum (double bubble sign) and little or no air in the rest of the small bowel. After correction of fluid and electrolyte imbalance, the obstructed segment should be bypassed by a duodenojejunostomy or other similar procedure. No attempt should be made to resect the obstructing pancreas, because a pancreatic fistula or acute pancreatitis often develops postoperatively. Occasionally, annular pancreas will present in adult life with similar symptoms. [5] Etienne D, John A, Menias CO, Ward R, Tubbs RS, Loukas M. Annular pancreas: a review of its molecular embryology, genetic basis and clinical considerat ions. Ann Anat. 2012 Sep;194(5):422-8. doi: 10.1016/j.aanat.2012.04.006. Epub 2012 May 17