The pancreas (French : pancréas) is a long, narrow, flattened gland of a reddish cream color, larger at one end than at the other, and lying across the posterior wall of the abdomen, behind the stomach, and opposite the first lumbar vertebra. Its larger end, the head, turned to the right, is embraced by the curvature of the duodenum, whilst its left or narrow extremity, the tail, reaches to a somewhat higher level, and is in contact with the spleen. The pancreas is an exocrine and endocrine gland. It is in contact with the lumbar column, therefore particularly exposed with the abdominal traumatisms.
The pancreas varies considerably, in different cases, in its size and weight. It is usually from 15 to 18 cm long, and 2cm in thickness, being thicker at its head and along its upper border than elsewhere. The weight of the gland, according to Kause and Cleudenning, is usually from 2.25 oz. to 3.5 oz. ; but Meckel has noted it as high as 6 oz., and Soemmerring as low as 1.5 oz.
The anterior surface of the pancreas is covered with the posterior wall of the sac of the omentum, and is concealed by the stomach, which glides upon it. The posterior surface is attached by areolar tissue to the vena cava, the aorta, the superior mesenteric artery and vein, the commencement of the vena portae, and the pillars of the diaphragm, all of which parts, besides many lymphatic vessels and glands, are interposed between it and the upper lumbar vertebrae: to the left of the vertebral column it is attached similarly to the left suprarenal capsule and kidney and to the renal vessels. Of the large vessels situated behind the pancreas, the superior mesenteric artery and vein are embraced by the substance of the gland, the lower extremity of the head curving somewhat behind them (This part of the gland is sometimes marked off from the rest, and is then named the lesser pancreas), so as sometimes to enclose these vessels in a complete canal, through which they pass downwards and forwards, and then emerge from beneath the lower border of the pancreas, between it and the termination of the duodenum. The coeliac axis is above the pancreas ; and in a groove along the upper border of the gland are placed the splenic artery and vein, the vein pursuing a straight, and the artery a tortuous course, and both supplying numerous branches to the pancreas, the narrow extremity of which is thus attached to the inner surface of the spleen. The head of the pancreas, embraced by the inner curved border of the duodenum, is attached more particularly to the descending and transverse portion of that intestine, encroaching slightly on both the anterior and posterior surface. The ductus communis choledochus passes down behind the head of the pancreas, and is generally received into a groove or canal in its substance.
The pancreas belongs to the class of compound racemose glands. In its general characters, and also in its intimate structure it closely resembles the salivary glands, to the description of the minute structure of which the reader is referred. It is somewhat looser and softer in its texture than those organs, the lobes and lobules being less compactly arranged.
The alveolar cells differ from those of the submaxillary gland in not containing- mucus, resembling in this respect the cells of the parotid: moreover, the columnar cells of the ducts appear to be devoid of the striated base seen in those of the submaxillary, and the ducts themselves have an irregular, angular shape: but in all essential points of structure, and in the distribution of the vessels and nerves, the two glands, as far as is known, entirely agree.
The principal excretory duct, called the pancreatic duct or canal of Wirsung (by whom it was discovered in the human subject in 1642), runs through the entire length of the gland, from left to right, buried completely in its substance, and placed rather nearer its lower than its upper border. Commencing by the union of the small ducts derived from the groups of lobules composing the tail of the pancreas, and receiving in succession at various angles, and from all sides, the ducts from the body of the gland, the canal of Wirsung increases in size as it advances towards the head of the pancreas, where, amongst other large branches, it is usually joined by one derived from that portion of the gland called the lesser pancreas. Curving slightly downwards, the pancreatic duct then comes into contact with the left side of the ductus communis choledochus, which it accompanies to the back part of the descending portion of the duodenum. Here the two ducts, placed side by side, pass very obliquely through the muscular and areolar coats of the intestine, and terminate, as already described, on its internal mucous surface, by a common orifice, situated at the junction of the descending and horizontal portions of the duodenum, between three and four inches below the pylorus. The pancreatic duct, with its branches, is readily distinguished from the glandular substance, by the very white appearance of its thin fibrous walls. Its widest part, near the duodenum, is from 1 line to 1.5 line in diameter, or nearly the size of an ordinary quill; but it may be easily distended beyond that size. It is lined by a remarkably thin and smooth mucous membrane, which -near the termination of the duct occasionally presents a few scattered recesses.
Sometimes the duct is double up to its point of entrance into the duodenum; and a still further deviation from the ordinary condition is not unfrequently observed, in which there is a supplementary duct, derived from the lesser pancreas or some part of the head of the gland, opening into the duodenum by a distinct orifice, at a distance of an inch or more from the termination of the principal duct. It sometimes occurs that the pancreatic duct and the common bile duct open separately into the duodenum.
Vessels and Nerves
Like the salivary glands, the pancreas receives its blood-vessels at numerous points. Its arteries are derived from the splenic and from the superior and inferior pancreatico-duodenal branches of the hepatic and superior mesenteric. Its blood is returned by the splenic and superior mesenteric veins. Its lymphatics terminate in the lumbar vessels and glands. The nerves of the pancreas are derived from the solar plexus.