Pancreas or Sweetbread

PANCREAS or SWEETBREAD, in anatomy, the pink tongue shaped, digestive gland which lies across the posterior wall of the abdomen about the level of the first lumbar vertebra behind, and the transpyloric plane in front (see ANATOMY : Superficial and Artistic). Its right end is a little to the right of the mid line of the abdomen and is curved round the superior mesenteric vessels, into the form of a This hook-like right end (the head) is adapted to the concavity of the duodenum. The first inch of the straight limb forms the neck and lies in front of the beginning of the portal vein, below the pyloric opening of the stomach and above the superior mesenteric vessels. The next three or four inches of the pancreas, form the body and this part lies in front of the left kidney and adrenal body, while it helps to form the posterior wall of the "stomach chamber" (see ALIMENTARY CANAL). At its left extremity the body tapers to form the tail, which usually touches the spleen (see DUCTLESS GLANDS) just below the hilum.

The pancreas is altogether behind the peritoneum. There is one main duct (the duct of Wirsung) which runs the whole length of the organ nearer the back than the front. As it reaches the head it turns downward and opens into the second part of the duode num, joining the common bile duct while they are both piercing the walls of the gut. A smaller accessory pancreatic duct com municates with the main duct.

The pancreas has no capsule, but is divided up into lobules held together by their ducts and by loose areolar tissue; the glands of which these lobules are made up are acino-tubular (see GLANDS). Small groups of epithelium-like cells without ducts (Islets of Langerhans) occur among the glandular tissue and are character istic of the pancreas. They are the source of insulin (q.v.) and degenerate in most cases of diabetes mellitus (q.v.).

Embryology.

The pancreas is developed, by three diverticula, from that part of the f oregut which will later form the duodenum. Of these diverticula the left ventral disappears early, but the right ventral, which is really an outgrowth from the lower part of the common bile duct, forms the head of the pancreas. The body and tail are formed from the dorsal diverticulum, and the two parts, at first separate, join one another so that the ducts communi cate, and eventually the ventral one takes almost all the secretion kith 411 rieal Inter. sec. to ttie a `'o rs of 4. t of ex.

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Comparative

the Acrania (Amphioxus) no representative of a pancreas has been found, but in the Cyclosto mata (hags and lampreys) there is a small lobular gland opening into the bile duct which probably represents it. In the Elasmo branchs (sharks and rays) there is a definite compact pancreas of considerable size. In the Teleostomi, which include the true bony fish (Teleostei), the sturgeon and Polyterus, the pancreas is some times a compact gland and sometimes diffuse between the layers of the mesentery ; at other times it is so surrounded by the liver as to be difficult to find. Among the Dipnoi (mud fish), Protop terus has it embedded in the walls of the stomach and intestine. The Amphibia have a definite compact pancreas, which lies in the U-shaped loop between the stomach and duodenum, and is massed round the bile duct. In the Reptilia there are sometimes several ducts, as in the crocodile and the water tortoise (Emys), and this arrangement is also found in birds. In mammals the gland is usually compact, though sometimes (rabbit) it is diffuse. It usually has two ducts, as in man, though in many animals (ox, sheep and goat) only one persists. When there is only one duct it may open with the common bile duct, e.g., sheep and cat, or may be very far away as in the ox and rabbit. (F. G. P.)