1911 Encyclopædia Britannica/Pancreas
PANCREAS (Gr. πᾶν, all; κρέας, flesh), or sweetbread, in
anatomy, the elongated, tongue-shaped, digestive gland, of a
pinkish colour, which lies across the posterior wall of the abdomen
about the level of the first lumbar vertebra behind, and of the
transpyloric plane in front (see Anatomy: Superficial and Artistic).
Its right end is only a little to the right of the mid line
of the abdomen and is curved down, round the superior medenteric
vessels, into the form of a 
. This hook-like right end
is known as the head of the pancreas, and its curvature is adapted
to the concavity of the duodenum (see fig.) The first inch of
the straight limb is narrower from above downward than the
rest and forms the neck. This part lies just in front of the
beginning of the portal vein, just below the pyloric opening of
the stomach and just above the superior mesenteric vessels.
The next three or four inches of the pancreas, to the left of the
neck, 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, and above the basal triangle of that viscus where the
splenic flexure of the colon is situated. On the upper border of
the body, a little to the left of the mid line of the abdomen, is
a convexity or hump, which is known as the tuber omentale
of the pancreas, and touches the elevation (bearing the same
name) on the liver.
The pancreas is altogether behind the peritoneum. In its greater part it is covered in front by the lesser sac (see Coelom and Serous Membranes), but the lower part of the front of the head and the very narrow lower surface of the body are in contact with the greater sac. There is one main duct of the pancreas, which is sometimes known as the duct of Wirsung; it is thin-walled and white, and 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 duodenum, joining the common bile duct while they are both piercing the walls of the gut. A smaller accessory pancreatic duct is found, which communicates with the main duct and usually opens into the duodenum about three-quarters of an inch above the papilla of the latter. It drains the lower part of the head, and either crosses or communicates with the duct of Wirsung to reach its opening (see A. M. Schirmer, Beitrag zur Geschichte und Anat. des Pancreas, Basel, 1893).
The pancreas has no real capsule, but is divided up into lobules, which are merely held together by their ducts and by loose areolar tissue; the glands of which these lobules are made up are of the acino-tubular variety (see Epithelial Tissues). Small groups of epithelium-like cells without ducts (Islets of Langerhans) occur among the glandular tissue and are characteristic of the pancreas. In cases of diabetes they sometimes degenerate. In the centre of each acinus of the main glandular tissue of the pancreas are often found spindle-shaped cells (centro-acinar cells of Langerhans). For details of microscopic structure see Essentials of Histology, by E. A. Schäfer (London, 1907).
Embryology.—The pancreas is developed, by three diverticula, from that part of the foregut which will later form the duodenum. Of these diverticula the left ventral disappears early,[1] 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 communicate, and eventually the ventral one takes almost all the secretion of the gland to the intestine, while that part of the dorsal one which is nearest the duodenum atrophies and forms the duct of Santorini. The main pancreatic duct (of Wirsung) is therefore formed partly by the ventral and partly by the dorsal diverticulum. As the diverticula grow they give off lateral branches, which branch again and again until the terminal buds form the acini of the gland. At first the pancreas grows upward, behind the stomach, between the two layers of the dorsal mesogastrium (see Coelom and Serous Membranes), but when the stomach and duodenum turn over to the right, the gland becomes horizontal and the opening of the right ventral diverticulum becomes more dorsal. Later, by the unequal growth of the duodenal walls, it comes to enter the gut on its left side where the papilla is permanently situated. After the turning over of the pancreas to the right the peritoneum is absorbed from its dorsal aspect. The islets of Langerhans are now regarded as portions of the glandular epithelium which have been isolated by the invasion and growth round them of mesenchyme (see Quain’s Anatomy, vol. i., 1908).
Comparative Anatomy.—In the Acrania (Amphioxus) no representative of a pancreas has been found, but in the Cyclostomata (hags and lampreys) there is a small lobular gland opening into the bile duct which probably represents it. In the Elasmobranchs (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 sometimes 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), Protopterus has it embedded in the walls of the stomach and intestine.
|
| From Ambrose Birmingham, Cunningham’s Text Book of Anatomy. |
| Fig. 1.—The Viscera and Vessels on the Posterior Abdominal Wall. |
| The stomach, liver and most of the intestines have been removed. The peritoneum has been preserved on the right kidney, and the fossa for the Spigelian lobe. In taking out the liver, the vena cava was left behind. The stomach-bed is well shown. (From a body hardened by chromic-acid injections.) |
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 (the pigeon, for instance, has three ducts opening into the duodenum at very different levels). In mammals the gland is usually compact, though sometimes, as in the rabbit, it is diffuse. It usually has two ducts, as in man, though in many animals, such as the 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.)
Diseases of the pancreas.—As the pancreas plays an important part in the physiology of digestion much attention has of late been paid to the question of its secretions. In sclerosis, atrophy, acute and chronic inflammatory changes and new growths in the pancreas an absence or lessening of its secretion may be evident. Haemorrhage into the pancreas is of some medico-legal importance as being a cause of death. The condition is rarely recognized in time for operative interference. Acute haemorrhagic pancreatitis is a combination of inflammation with haemorrhage in which the pancreas is found enlarged and infiltrated with blood. Violent pain, vomiting and collapse, are the chief features as is also the case in pancreatic abscess in which the abscess may be single or multiple. In the latter case operation has been followed by recovery. Haemorrhagic inflammation has been followed by gangrene of the pancreas, which usually terminates fatally. In two remarkable cases, however, reported by Chiari recovery followed on the discharge per rectum of the necrosed pancreas. Chronic pancreatitis is said by Mayo Robson to occur in connexion with the symptoms of catarrhal jaundice, which he suggests is due to the pressure on the common duct by the swollen pancreatic tissue. The organ is enlarged and very hard, and the symptoms are pain, dyspepsia, jaundice, loss of weight and the presence of fat in the stools. This latter sign is common to all forms of pancreatic disease. In connexion with all pancreatic diseases small yellowish patches are found in the pancreatic tissue, mesentery, omentum and abdominal fatty tissue generally, and the tissues appear to be studded with whitish areas often not larger than a pin’s head. The condition, which was first observed by Balser, has been termed “fat-necrosis.” The pancreas like other organs, is subject to the occurrence of new growths, tumours and cysts, syphilis and tuberculosis.
- ↑ N. W. Ingalls has shown (Archiv. f. mik. Anat. und Entwickl. Bd. 70, 1907), that in a human embryo of 4·9 mm. the two ventral buds persist and join one another below the liver bud.