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Pancreas
Illu pancrease.svg
Illu pancreas duodenum.jpg
1: Head of pancreas
2: Uncinate process of pancreas
3: Pancreatic notch
4: Body of pancreas
5: Anterior surface of pancreas
6: Inferior surface of pancreas
7: Superior margin of pancreas
8: Anterior margin of pancreas
9: Inferior margin of pancreas
10: Omental tuber
11: Tail of pancreas
12: Duodenum
Gray's subject #251 1199
Artery inferior pancreaticoduodenal artery, superior pancreaticoduodenal artery, splenic artery
Vein pancreaticoduodenal veins, pancreatic veins
Nerve pancreatic plexus, celiac ganglia, vagus[1]
Precursor pancreatic buds
MeSH Pancreas
Dorlands/Elsevier Pancreas

The pancreas is a gland organ in the digestive and endocrine system of vertebrates. It is both an endocrine gland producing several important hormones, including insulin, glucagon, and somatostatin, as well as an exocrine gland, secreting pancreatic juice containing digestive enzymes that pass to the small intestine. These enzymes help in the further breakdown of the carbohydrates, protein, and fat in the chyme.

Contents

Histology

Under a microscope, stained sections of the pancreas reveal two different types of parenchymal tissue.[2] Lightly staining clusters of cells are called islets of Langerhans, which produce hormones that underlie the endocrine functions of the pancreas. Darker staining cells form acini connected to ducts. Acinar cells belong to the exocrine pancreas and secrete digestive enzymes into the gut via a system of ducts.

Structure Appearance Function
Islets of Langerhans Lightly staining, large, spherical clusters Hormone production and secretion (endocrine pancreas)
Pancreatic acini Darker staining, small, berry-like clusters Digestive enzyme production and secretion (exocrine pancreas)

Function

The pancreas is a dual-function gland, having features of both endocrine and exocrine glands.

Endocrine

The part of the pancreas with endocrine function is made up of approximately a million[3] cell clusters called islets of Langerhans. Four main cell types exist in the islets. They are relatively difficult to distinguish using standard staining techniques, but they can be classified by their secretion: α cells secrete glucagon(increase Glucose in blood), β cells secrete insulin (decrease Glucose in blood), δ cells secrete somatostatin (regulates/stops α and β cells), and PP cells secrete pancreatic polypeptide.[4]

The islets are a compact collection of endocrine cells arranged in clusters and cords and are crisscrossed by a dense network of capillaries. The capillaries of the islets are lined by layers of endocrine cells in direct contact with vessels, and most endocrine cells are in direct contact with blood vessels, by either cytoplasmic processes or by direct apposition. According to the volume The Body, by Alan E. Nourse,[5] the islets are "busily manufacturing their hormone and generally disregarding the pancreatic cells all around them, as though they were located in some completely different part of the body."

Exocrine

In contrast to the endocrine pancreas, which secretes hormones into the blood, the exocrine pancreas produces digestive enzymes and an alkaline fluid (referred to as pancreatic juice), and secretes them into the small intestine through a system of exocrine ducts in response to the small intestine hormones secretin and cholecystokinin. Digestive enzymes include trypsin, chymotrypsin, pancreatic lipase, and pancreatic amylase, and are produced and secreted by acinar cells of the exocrine pancreas. Specific cells that line the pancreatic ducts, called centroacinar cells, secrete a bicarbonate- and salt-rich solution into the small intestine.[6]

Regulation

The pancreas receives regulatory innervation via hormones in the blood and through the autonomic nervous system. These two inputs regulate the secretory activity of the pancreas.

Sympathetic (adrenergic) Parasympathetic (muscarinic)
α2: decreases secretion from beta cells, increases secretion from alpha cells M3[7] increases stimulation of alpha cells and beta cells

Diseases of the pancreas

Because the pancreas is a storage depot for digestive enzymes, injury to the pancreas is potentially very dangerous. A puncture of the pancreas generally requires prompt and experienced medical intervention.

Pancreatic cancer, particularly cancers of the Exocrine Pancreas remain one of the most deadly cancers, and the mortality rate is very high.

History

The pancreas was first identified for western civilization by Herophilus (335–280 BC), a Greek anatomist and surgeon. Only a few hundred years later, Ruphos, another Greek anatomist, gave the pancreas its name. The term "pancreas" is derived from the Greek πᾶν ("all", "whole"), and κρέας ("flesh").[8] – presumably because of its fleshy consistency.

Embryological development

Schematic illustrating the development of the pancreas from a dorsal and a ventral bud. During maturation the ventral bud flips to the other side of the gut tube (arrow) where it typically fuses with the dorsal lobe. An additional ventral lobe which usually regress during development is omitted.

The pancreas forms from the embryonic foregut and is therefore of endodermal origin. Pancreatic development begins the formation of a ventral and dorsal anlage (or buds). Each structure communicates with the foregut through a duct. The ventral pancreatic bud becomes the head and uncinate process, and comes from the hepatic diverticulum.

Differential rotation and fusion of the ventral and dorsal pancreatic buds results in the formation of the definitive pancreas.[9] As the duodenum rotates to the right, it carries with it the ventral pancreatic bud and common bile duct. Upon reaching its final destination, the ventral pancreatic bud fuses with the much larger dorsal pancreatic bud. At this point of fusion, the main ducts of the ventral and dorsal pancreatic buds fuse, forming the duct of Wirsung, the main pancreatic duct.

Differentiation of cells of the pancreas proceeds through two different pathways, corresponding to the dual endocrine and exocrine functions of the pancreas. In progenitor cells of the exocrine pancreas, important molecules that induce differentiation include follistatin, fibroblast growth factors, and activation of the Notch receptor system.[9] Development of the exocrine acini progresses through three successive stages. These include the predifferentiated, protodifferentiated, and differentiated stages, which correspond to undetectable, low, and high levels of digestive enzyme activity, respectively.

Progenitor cells of the endocrine pancreas arise from cells of the protodifferentiated stage of the exocrine pancreas.[9] Under the influence of neurogenin-3 and Isl-1, but in the absence of Notch receptor signaling, these cells differentiate to form two lines of committed endocrine precursor cells. The first line, under the direction of Pax-0, forms α- and γ- cells, which produce the peptides glucagon and pancreatic polypeptide, respectively. The second line, influenced by Pax-6, produces β- and δ-cells, which secrete insulin and somatostatin, respectively.

Insulin and glucagon can be detected in the fetal circulation by the fourth or fifth month of fetal development.[9]

In non-human animals

Pancreatic tissue is present in all vertebrate species, but its precise form and arrangement varies widely. There may be up to three separate pancreases, two of which arise from ventral buds, and the other dorsally. In most species (including humans), these fuse in the adult, but there are several exceptions. Even when a single pancreas is present, two or three pancreatic ducts may persist, each draining separately into the duodenum (or equivalent part of the hindgut). Birds, for example, typically have three such ducts.[10]

In teleosts, and a few other species (such as rabbits), there is no discrete pancreas at all, with pancreatic tissue being distributed diffusely across the mesentery and even within other nearby organs, such as the liver or spleen. In a few teleost species, the endocrine tissue has fused to form a distinct gland within the abdominal cavity, but otherwise it is distributed amongst the exocrine components. The most primitive arrangement, however, appears to be that of lampreys and lungfish, in which pancreatic tissue is found as a number of discrete nodules within the wall of the gut itself, with the exocrine portions being little different from other glandular structures of the intestine.[10]

Additional images

References

  1. ^ Physiology at MCG 6/6ch2/s6ch2_30
  2. ^ Histology at BU 10404loa
  3. ^ Hellman B, Gylfe E, Grapengiesser E, Dansk H, Salehi A (2007). "[Insulin oscillations--clinically important rhythm. Anti-diabetics should increase the pulsative component of the insulin release]" (in Swedish). Lakartidningen 104 (32-33): 2236–9. PMID 17822201. 
  4. ^ BRS physiology 4th edition ,page 255-256, Linda S. Constanzo, Lippincott publishing
  5. ^ The Body, by Alan E. Nourse, in the Time-Life Science Library Series (op. cit., p. 171.)
  6. ^ Maton, Anthea; Jean Hopkins, Charles William McLaughlin, Susan Johnson, Maryanna Quon Warner, David LaHart, Jill D. Wright (1993). Human Biology and Health. Englewood Cliffs, New Jersey, USA: Prentice Hall. ISBN 0-13-981176-1. OCLC 32308337. 
  7. ^ Verspohl EJ, Tacke R, Mutschler E, Lambrecht G (1990). "Muscarinic receptor subtypes in rat pancreatic islets: binding and functional studies". Eur. J. Pharmacol. 178 (3): 303–11. doi:10.1016/0014-2999(90)90109-J+. PMID 2187704. 
  8. ^ Harper, Douglas. "Pancreas". Online Etymology Dictionary. http://www.etymonline.com/index.php?term=pancreas. Retrieved 2007-04-04. 
  9. ^ a b c d Carlson, Bruce M. (2004). Human embryology and developmental biology. St. Louis: Mosby. pp. 372–4. ISBN 0-323-01487-9. 
  10. ^ a b Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. pp. 357-359. ISBN 0-03-910284-X. 

1911 encyclopedia

Up to date as of January 14, 2010

From LoveToKnow 1911

Medical warning!
This article is from the 1911 Encyclopaedia Britannica. Medical science has made many leaps forward since it has been written. This is not a site for medical advice, when you need information on a medical condition, consult a professional instead.

PANCREAS (Gr. ra y, all; rcpas, 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 C". 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 threequarters 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 and 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. Schafer (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,' 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 I N. W. Ingalls has shown (Archiv. f. mik. Anat. and 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.

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.

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 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 Aorta jejunal flexure Gastro duodenal artery and neck N, of pancreas Superior mesenteric artery Duodenum Head of pancreas vein Ureter s ?Y Inferior mesen-,/ teric artery Spermatic vein Ureter Right common iliac vein Right common iliac .

artery Left common iliac vein Ureter Colon Fossa for Spigelian lobe Right phrenic.vessels Vena cava Hepatic vein Hepatic artery Portal vein Pylorus Bile duct Right suprarenal capsule OEsophagus.

Coronary artery Diaphragm Left suprarenal capsule Splenic artery Kidney Upper surface of pancreas Gastric surface of spleen Under surface of pancreas Attachment of transverse mesocolon From Ambrose Birmingham, Cunningham's 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 chromicacid injections.) 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 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.


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Simple English

The pancreas is an organ that releases hormones and enzymes to help digestion.

It releases substances through special cells called the Islets of Langerhans.

The pancreas belongs to two systems of function (the digestive system due to its role in breaking down nutrients and the endocrine system for its role in hormone production).

Hormones

The pancreas releases these hormones:

  • Insulin (which assists in the breaking down of carbohydrate)
  • Glucagon (which increases the glucose or sugar in the blood)
  • Somatostatin (which reduces production of insulin and glucagon)
  • (the pancreas is behind the liver and mostly on the right side of your body)

Digestive enzymes

The pancreas releases many different enzymes to help digestion:

  • Lipase (which breaks down fats)
  • Amylase (which breaks down carbohydrates)
  • Trypsinogen and Chymotrypsin (which break down proteins)
  • Erepsin, which digests peptones into amino acids.

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