Pancreas, a single, non-symmetrical glandular organ, situated in man transversely across the upper part of the abdomen, about on the level of the last dorsal vertebra; it is behind the peritoneum, at the posterior part of the epigastric region, on the spine and great vessels, between the three portions of the duodenum, behind the stomach, and on the right of the spleen. It is of an irregular, elongated form, flattened from before backward, the left extremity very thin and prolonged to and sometimes beneath the spleen; the right extremity rounded, resting against the second portion of the duodenum; the color is grayish white; the length is about 7 in., width 1 1/2, and thickness 1 in., and the weight 3 to 4 oz.; it is rather smaller in woman. The duct is in the interior, going from left to right, receiving in its course the excretory canal which comes from the larger end, or little pancreas as it is sometimes called; it opens into the duodenum, at the lower part of the second curve, by a special orifice, or one common to it and the bile duct; its arteries come principally from the splenic branch of the cceliac axis, and its nerves from the solar plexus.
It closely resembles in structure the salivary glands, like the parotid; it is made up of clusters of secreting follicles forming the ends of the finely branching divisions of the duct; each cluster, with its vessels, nerves, and connecting areolar tissue, forms a lobule, and the several lobules are held together by the ducts, vessels, and areolar tissue; its development begins by a budding forth of cells from the intestinal canal. The secretion of the pancreas, called the pancreatic juice, is a colorless, alkaline fluid, possessing a considerable degree of viscidity; it consists of nearly 10 per cent, of solid matters, of which by far the most abundant and important is an organic substance, termed pancreatine, resembling albumen in being coagulable by heat, by nitric acid, and by alcohol, but differing from it in being also coagulable by sulphate of magnesia in excess. The pancreatic juice has been obtained in the lower animals by introducing a silver canula into the pancreatic duct, and collecting the fluid discharged from its orifice during digestion.
Its most remarkable property is that, when brought in contact with oleaginous matters, it at once reduces them to a state of emulsion, the fatty substance being broken up into finely divided particles, and held suspended in this condition in the animal fluid; this intimate mixture of the oily and albuminoid matters forms a white, opaque, milky liquid, and is known as the chyle; it is also true that the chyle makes its appearance in the intestines only after the pancreatic juice has had access to the alimentary matters. From these experiments there is little doubt that the main office of the pancreatic juice in digestion is to act upon the oleaginous ingredients of the food, and to prepare them for absorption by the emulsifying process. (See Chyle, and Digestion.) The daily quantity of pancreatic juice secreted and discharged into the intestine is estimated at rather more than half a pound in the dog, and between a pound and a half and two pounds in the human subject; the secretion is most abundant at the commencement of and during the digestive process, and the probability is that it is very much diminished, if it does not cease entirely, in the intervals of digestion.
The pancreas is liable to hypertrophy, atrophy, softening, induration, inflammation extending from neighboring organs, simple and malignant tumors, fatty degeneration, and calculous growth. That it performs some essential function is evident from its existence in all vertebrates, whether carnivorous or herbivorous, and from its presenting a constant relation to the duodenum, whatever be the proportions of the alimentary canal or the form of the organ; it is even found in a rudimentary condition in the invertebrates, and as low as the worms Rotatoria); also in the annelids proper, the gasteropod and ce-phalopod mollusks, and in many insects; it exists here as caecal appendages with thick walls, lined with ciliated epithelium, and opening into the beginning of the intestine. The pyloric csecal appendages of most osseous fishes have generally been regarded by anatomists as the analogue of a pancreas; they become more and more numerous and complex, from the simple ones in the turbot to the 60 in the salmon with a secreting surface of more than 32 ft.; in the sturgeon they become united into a glandular organ. In some orders these caeca are absent, as in the sharks and rays, pike, and eel, in which the pancreas has the ordinary glandular form.
Some authors deny the pancreatic nature of these caeca, and maintain that they secrete a fluid only accessory to the true pancreatic secretions. In reptiles the pancreas is always present, often large, and in the higher orders more or less in contact with the spleen. In birds it is larger than in any other class, and it probably performs also the office of salivary glands, which are here wanting; it communicates with the intestinal canal by two or three openings; as a general rule the pancreatic secretion is poured in before the bile, though the ducts are so near together that no physiological conclusions can be drawn as to their separate actions; the greatest separation is probably in the ostrich, in which the bile duct opens close to the pylorus and the pancreatic duct 3 ft. lower down; it is generally whitish red, large, elongated, and usually with two lobes. In mammals it differs from that of man chiefly in color and in its more or less division into lobes; in rodents, and especially in the rat, it is spread out in an arborescent manner; in the rabbit the duct enters the intestine from 9 to 13 in. from the pylorus, affording special facilities for studying its secretion, since in this animal it has been found that the chyle does not make its appearance in the intestine or the lacteals until the food has passed the orifice of the pancreatic duct; in other species, where this duct opens into the intestine higher up, the chyle is also found at a higher level.
The pancreas is often called sweetbread in the calf, but this term more properly belongs to the thymus gland.
Thc Spleen (Spl.) with the splenic artery (Sp. A.). Below this is seen the splenic vein running to help to form the vena portce ( V. P.). Ao., the aorta; D., a pillar of the diaphragm; P. D., the pancreatic duct exposed by dissection in the substance of the pancreas; Zhn., the duodenum; B. D., the biliary duct opening with the pancreatic duct at x; y, the intestinal vessels.