Pancreas

This is a good article. Click here for more information.
Source: Wikipedia, the free encyclopedia.
For other uses, see Pancreas (disambiguation).

Pancreas
Splenic lymph nodes, celiac lymph nodes and superior mesenteric lymph nodes
Identifiers
Latinpancreas
GreekΠάνκρεας (Pánkreas)
MeSHD010179
TA98A05.9.01.001
TA23114
FMA7198
Anatomical terminology]

The pancreas is an

fats
in food entering the duodenum from the stomach.

Inflammation of the pancreas is known as

diabetes mellitus. Pancreatic cancer can arise following chronic pancreatitis
or due to other reasons, and carries a very poor prognosis, as it is often only identified after it has spread to other areas of the body.

The word pancreas comes from the Greek πᾶν (pân, "all") & κρέας (kréas, "flesh"). The function of the pancreas in diabetes has been known since at least 1889, with its role in insulin production identified in 1921.

Structure

The pancreas (shown here in pink) sits behind the stomach, with the body near the curvature of the duodenum, and the tail stretching to touch the spleen.

The pancreas is an organ that in humans lies in the abdomen, stretching from behind the stomach to the left upper abdomen near the spleen. In adults, it is about 12–15 centimetres (4.7–5.9 in) long, lobulated, and salmon-coloured in appearance.[7]

Anatomically, the pancreas is divided into a head, neck, body, and tail. The pancreas stretches from the inner curvature of the duodenum, where the head surrounds two blood vessels: the superior mesenteric artery and vein. The longest part of the pancreas, the body, stretches across behind the stomach, and the tail of the pancreas ends adjacent to the spleen.[7]

Two ducts, the

accessory pancreatic duct opens into duodenum with separate openings located above the opening of the main pancreatic duct.[7]

Parts

The head of the pancreas sits within the curvature of the duodenum, and wraps around the superior mesenteric artery and vein. To the right sits the descending part of the duodenum, and between these travel the superior and inferior pancreaticoduodenal arteries. Behind rests the inferior vena cava, and the common bile duct. In front sits the peritoneal membrane and the transverse colon.[7] A small uncinate process emerges from below the head, situated behind the superior mesenteric vein and sometimes artery.[7]

The neck of the pancreas separates the head of the pancreas, located in the curvature of the duodenum, from the body. The neck is about 2 cm (0.79 in) wide, and sits in front of where the

anterior superior pancreaticoduodenal artery travels in front of the neck of the pancreas.[7]

The body is the largest part of the pancreas, and mostly lies behind the stomach, tapering along its length. The peritoneum sits on top of the body of the pancreas, and the

suspensory ligament of the duodenum which falls between these two. In front of the pancreas sits the transverse colon.[8]

The pancreas narrows towards the tail, which sits near to the spleen.

ligament between the spleen and the left kidney. The splenic artery and vein, which also passes behind the body of the pancreas, pass behind the tail of the pancreas.[7]

Blood supply

The pancreas has a rich blood supply, with vessels originating as branches of both the

inferior pancreaticoduodenal arteries run along the back and front surfaces of the head of the pancreas adjacent to the duodenum. These supply the head of the pancreas. These vessels join together (anastamose) in the middle.[7]

The body and neck of the pancreas drain into the

pancreaticoduodenal veins.[7]

The pancreas drains into lymphatic vessels that travel alongside its

splenic lymph nodes, and eventually into lymph nodes that lie in front of the aorta, between the coeliac and superior mesenteric arteries. The lymphatic vessels of the head and neck drain into intermediate lymphatic vessels around the pancreaticoduodenal, mesenteric and hepatic arteries, and from there into the lymph nodes that lie in front of the aorta.[7]

Microanatomy

pancreatic islet when pancreatic tissue is stained and viewed under a microscope. Parts of the digestive ("exocrine") pancreas can be seen around the islet, more darkly. These contain hazy dark purple granules of inactive digestive enzymes (zymogens
).
A pancreatic islet that uses fluorescent antibodies to show the location of different cell types in the pancreatic islet. Antibodies against glucagon, secreted by alpha cells, show their peripheral position. Antibodies against insulin, secreted by beta cells, show the more widespread and central position that these cells tend to have.[9]

The pancreas contains tissue with an

exocrine role, and this division is also visible when the pancreas is viewed under a microscope.[10]

The majority of pancreatic tissue has a digestive role. The cells with this role form clusters (

column-shaped cells. There is more than one layer of cells as the diameter of the ducts increases.[10]

The tissues with an

systemic circulation.[9]

Variation

The size of the pancreas varies considerably.

accessory pancreatic duct may be present if the main duct of the dorsal bud of the pancreas does not regress; this duct opens into the minor duodenal papilla.[11] If the two buds themselves, each having a duct, do not fuse, a pancreas may exist with two separate ducts, a condition known as a pancreas divisum. This condition has no physiologic consequence.[12] If the ventral bud does not fully rotate, an annular pancreas may exist, where part or all of the duodenum is encircled by the pancreas. This may be associated with duodenal atresia.[13]

Gene and protein expression

Further information: Bioinformatics § Gene and protein expression

10,000 protein coding genes (~50% of all human genes) are expressed in the normal human pancreas.[14][15] Less than 100 of these genes are specifically expressed in the pancreas. Similar to the salivary glands, most pancreas-specific genes encode for secreted proteins. Corresponding pancreas-specific proteins are either expressed in the exocrine cellular compartment and have functions related to digestion or food uptake such as digestive chymotrypsinogen enzymes and pancreatic lipase PNLIP, or are expressed in the various cells of the endocrine pancreatic islets and have functions related to secreted hormones such as insulin, glucagon, somatostatin and pancreatic polypeptide.[16]

Development

digestive tract, as a dorsal and ventral
bud. As it develops, the ventral bud rotates to the other side and the two buds fuse together.

The pancreas forms during development from two buds that arise from the duodenal part of the foregut, an embryonic tube that is a precursor to the gastrointestinal tract.[11] It is of endodermal origin.[11] Pancreatic development begins with the formation of a dorsal and ventral pancreatic bud. Each joins with the foregut through a duct. The dorsal pancreatic bud forms the neck, body, and tail of the developed pancreas, and the ventral pancreatic bud forms the head and uncinate process.[11]

The definitive pancreas results from rotation of the ventral bud and the fusion of the two buds.

main pancreatic duct.[11]

Cellular development

Pancreatic progenitor cells are precursor cells that differentiate into the functional pancreatic cells, including exocrine acinar cells, endocrine islet cells, and ductal cells.[17] These progenitor cells are characterised by the co-expression of the transcription factors PDX1 and NKX6-1.[17]

The cells of the exocrine pancreas differentiate through molecules that induce differentiation including

Notch receptor system.[17] Development of the exocrine acini progresses through three successive stages. These are the predifferentiated, protodifferentiated, and differentiated stages, which correspond to undetectable, low, and high levels of digestive enzyme activity, respectively.[17]

Pancreatic progenitor cells differentiate into endocrine islet cells under the influence of

Pax-6, the endocrine precursor cells differentiate to form beta and delta cells.[17] The pancreatic islets form as the endocrine cells migrate from the duct system to form small clusters around capillaries.[9] This occurs around the third month of development,[11] and insulin and glucagon can be detected in the human fetal circulation by the fourth or fifth month of development.[17]

Function

The pancreas is involved in

blood sugar control and metabolism within the body, and also in the secretion of substances (collectively pancreatic juice) that help digestion. These are divided into an "endocrine" role, relating to the secretion of insulin and other substances within pancreatic islets that help control blood sugar levels and metabolism within the body, and an "exocrine" role, relating to the secretion of enzymes involved in digesting substances in the digestive tract.[10]

Blood glucose regulation

See also: Pancreatic islets
The pancreas maintains constant blood glucose levels (shown as the waving line). When the blood glucose level is too high, the pancreas secretes insulin and when the level is too low, the pancreas secretes glucagon.

Cells within the pancreas help to maintain blood glucose levels (homeostasis). The cells that do this are located within the pancreatic islets that are present throughout the pancreas. When blood glucose levels are low, alpha cells secrete glucagon, which increases blood glucose levels. When blood glucose levels are high beta cells secrete insulin to decrease glucose in blood. Delta cells in the islet also secrete somatostatin which decreases the release of insulin and glucagon.[9]

Glucagon acts to increase glucose levels by promoting the

depolarisation of the cell membrane which stimulates the release of the insulin.[18]

The main factor influencing the secretion of insulin and glucagon are the levels of glucose in blood plasma.

Alpha-1 receptors inhibits secretion.[19] M3 receptors of the parasympathetic nervous system act when stimulated by the right vagus nerve to stimulate release of insulin from beta cells.[19]

Digestion

pancreatic islet, part of the endocrine pancreas, which contains cells responsible for secretion of insulin and glucagon
.

The pancreas plays a vital role in the

intralobular ducts, which drain to the main pancreatic duct, which drains directly into the duodenum. About 1.5 - 3 liters of fluid are secreted in this manner every day.[8][21]

The cells in each acinus are filled with granules containing the digestive enzymes. These are secreted in an inactive form termed

enterokinase present in the lining of the duodenum. The proenzymes are cleaved, creating a cascade of activating enzymes.[21]

These enzymes are secreted in a fluid rich in

Ito cells of the lining of the duodenum and jejunum mostly in response to long chain fatty acids, and increases the effects of secretin.[21] At a cellular level, bicarbonate is secreted from centroacinar and ductal cells through a sodium and bicarbonate cotransporter that acts because of membrane depolarisation caused by the cystic fibrosis transmembrane conductance regulator. Secretin and VIP act to increase the opening of the cystic fibrosis transmembrane conductance regulator, which leads to more membrane depolarisation and more secretion of bicarbonate.[22][23][24]

A variety of mechanisms act to ensure that the digestive action of the pancreas does not act to digest pancreatic tissue itself. These include the secretion of inactive enzymes (zymogens), the secretion of the protective enzyme trypsin inhibitor, which inactivates trypsin, the changes in pH that occur with bicarbonate secretion that stimulate digestion only when the pancreas is stimulated, and the fact that the low calcium within cells causes inactivation of trypsin.[21]

Additional functions

The pancreas also secretes vasoactive intestinal peptide and pancreatic polypeptide. Enterochromaffin cells of the pancreas secrete the hormones motilin, serotonin, and substance P.[9]

Clinical significance

Main article: Pancreatic disease

Inflammation

Main article: Pancreatitis

Inflammation of the pancreas is known as

very high blood triglyceride levels. Acute pancreatitis is likely to cause intense pain in the central abdomen, that often radiates to the back, and may be associated with nausea or vomiting. Severe pancreatitis may lead to bleeding or perforation of the pancreas resulting in shock or a systemic inflammatory response syndrome, bruising of the flanks or the region around the belly button. These severe complications are often managed in an intensive care unit.[25]

In pancreatitis, enzymes of the exocrine pancreas damage the structure and tissue of the pancreas. Detection of some of these enzymes, such as amylase and lipase in the blood, along with symptoms and findings on medical imaging such as ultrasound or a CT scan, are often used to indicate that a person has pancreatitis. Pancreatitis is often managed medically with pain reliefs, and monitoring to prevent or manage shock, and management of any identified underlying causes. This may include removal of gallstones, lowering of blood triglyceride or glucose levels, the use of corticosteroids for autoimmune pancreatitis, and the cessation of any medication triggers.[25]

enzyme replacement may be needed to prevent malabsorption.[25]

Cancer

Main article: Pancreatic cancer
Pancreatic cancer, shown here, most commonly occurs as an adenocarcinoma in the head of the pancreas. Because symptoms (such as skin yellowing, pain, or itch) do not occur until later in the disease, it often presents at a later stage and has limited treatment options.
Relative incidences of various pancreatic neoplasms, with pancreatic cancers in red/pink color.[26]

hereditary nonpolyposis colon cancer and dysplastic nevus syndrome among others.[25][28] About 25% of cases are attributable to tobacco smoking,[29] while 5–10% of cases are linked to inherited genes.[27]

Pancreatic adenocarcinoma is the most common form of pancreatic cancer, and is cancer arising from the exocrine digestive part of the pancreas. Most occur in the head of the pancreas.

ERCP or ultrasound can be used to confirm an uncertain diagnosis.[25]

Because of the late development of symptoms, most cancer presents at an advanced

ERCP to facilitate the drainage of bile, and medications to help control pain.[25] In the United States pancreatic cancer is the fourth most common cause of deaths due to cancer.[30] The disease occurs more often in the developed world, which had 68% of new cases in 2012.[31] Pancreatic adenocarcinoma typically has poor outcomes with the average percentage alive for at least one and five years after diagnosis being 25% and 5% respectively.[31][32] In localized disease where the cancer is small (< 2 cm) the number alive at five years is approximately 20%.[33]

There are several types of pancreatic cancer, involving both the endocrine and exocrine tissue. The many types of

pancreatic endocrine tumors are all uncommon or rare, and have varied outlooks. However the incidence of these cancers has been rising sharply; it is not clear to what extent this reflects increased detection, especially through medical imaging, of tumors that would be very slow to develop. Insulinomas (largely benign) and gastrinomas are the most common types.[34] For those with neuroendocrine cancers the number alive after five years is much better at 65%, varying considerably with type.[31]

A solid pseudopapillary tumour is a low-grade malignant tumour of the pancreas of papillary architecture that typically afflicts young women.[35]

Diabetes mellitus

Type 1 diabetes

Main article:
Diabetes mellitus type 1

blood sugar levels within optimal ranges, and its lack can lead to high blood sugar. As an untreated chronic condition, complications including accelerated vascular disease, diabetic retinopathy, kidney disease and neuropathy can result.[36] In addition, if there is not enough insulin for glucose to be used within cells, the medical emergency diabetic ketoacidosis, which is often the first symptom that a person with type 1 diabetes may have, can result.[37] Type 1 diabetes can develop at any age but is most often diagnosed before age 40.[36] For people living with type 1 diabetes, insulin injections are critical for survival.[36] An experimental procedure to treat type 1 diabetes is pancreas transplantation or isolated transplantation of islet cells to supply a person with functioning beta cells.[36]

Type 2 diabetes

Main article:
Diabetes mellitus type 2

Diabetes mellitus type 2 is the most common form of diabetes.[36] The causes for high blood sugar in this form of diabetes usually are a combination of insulin resistance and impaired insulin secretion, with both genetic and environmental factors playing a role in the development of the disease.[38] Over time, pancreatic beta cells may become "exhausted" and less functional.[36] The management of type 2 diabetes involves a combination of lifestyle measures, medications if required and potentially insulin.[39] With relevance to the pancreas, several medications act to enhance the secretion of insulin from beta cells, particularly

DPP-4 inhibitors, which slow the breakdown of incretins.[39]

Removal

It is possible for a person to live without a pancreas, provided that the person takes insulin for proper regulation of blood glucose concentration and pancreatic enzyme supplements to aid digestion.[40]

History

The pancreas was first identified by

anatomist and surgeon.[41] A few hundred years later, Rufus of Ephesus, another Greek anatomist, gave the pancreas its name. Etymologically, the term "pancreas", a modern Latin adaptation of Greek πάγκρεας,[42] [πᾶν ("all", "whole"), and κρέας ("flesh")],[43] originally means sweetbread,[44] although literally meaning all-flesh, presumably because of its fleshy consistency. It was only in 1889 when Oskar Minkowski discovered that removing the pancreas from a dog caused it to become diabetic.[45] Insulin was later isolated from pancreatic islets by Frederick Banting and Charles Best in 1921.[45]

The way the tissue of the pancreas has been viewed has also changed. Previously, it was viewed using simple staining methods such as H&E stains. Now, immunohistochemistry can be used to more easily differentiate cell types. This involves visible antibodies to the products of certain cell types, and helps identify with greater ease cell types such as alpha and beta cells.[9]

Other animals

Pancreatic tissue is present in all

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 foregut). Birds, for example, typically have three such ducts.[46]

In teleost fish, 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 among 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.[46]

Cuisine

The pancreas of calf (ris de veau) or lamb (ris d'agneau), and, less commonly, of beef or pork, are used as food under the culinary name of sweetbread.[47][48]

Additional images

  • A normal pancreas on ultrasound.
    A normal pancreas on ultrasound.
  • Identifying pancreas on abdominal ultrasonography when it is partly obscured by bowel gas.
    Identifying pancreas on abdominal ultrasonography when it is partly obscured by bowel gas.
  • Pancreas of a human embryo at end of sixth week
    Pancreas of a human embryo at end of sixth week
  • The pancreas and its surrounding structures
    The pancreas and its surrounding structures
  • Duodenum and pancreas. Deep dissection.
    Duodenum and pancreas. Deep dissection.

References

This article uses anatomical terminology.
  1. ^ Nosek, Thomas M. "Section 6/6ch2/s6ch2_30". Essentials of Human Physiology. Archived from the original on 2016-03-24.
  2. PMID 2865807
    .
  3. ^ "Pancreas Gland - Endocrine System". Innerbody. Retrieved 2021-06-12.
  4. ^ Beger's 2018, pp. 124.
  5. ^ "Endocrine Pancreas - an overview ScienceDirect Topics". www.sciencedirect.com. Retrieved 2021-06-12.
  6. PMID 6111521
    .
  7. ^ a b c d e f g h i j k l m n o p q r Gray's 2016, pp. 1179–1189.
  8. ^ a b Gray's 2008, pp. 1183–1190.
  9. ^ a b c d e f g h i Wheater's Histology 2013, pp. 332–333.
  10. ^ a b c Wheater's Histology 2013, pp. 287–291.
  11. ^
    ISBN 9781496383907
    .
  12. ^ Kanth, Rajan; Roy, Praveen K; Al Samman, Mounzer; Patti, Marco G (2019-11-21). "Pancreatic Divisum: Pathophysiology". emedicine.medscape.com. Medscape.
  13. PMID 26388905
    .
  14. ^ "The human proteome in pancreas – The Human Protein Atlas". www.proteinatlas.org. Retrieved 2017-09-25.
  15. S2CID 802377
    .
  16. PMID 25546435
    .
  17. ^
    ISBN 978-0323523752
    .
  18. ^ a b Harrison's 2015, pp. 2853–4.
  19. ^
    OCLC 1076268769.{{cite book}}: CS1 maint: location missing publisher (link
    )
  20. ISBN 978-1-4557-7016-8
    .
  21. ^ a b c d e f g h Harrison's 2015, pp. 2086–2102.
  22. ^ Harrison's 2015, pp. 2090.
  23. ^ Beger's 2018, pp. 16, 57.
  24. PMID 21634067. Archived
    from the original on Nov 18, 2022.
  25. ^ a b c d e f g h i j k Davidson's 2018, p. 837-844.
  26. PMID 21721197
    .
    Diagram by Mikael Häggström, M.D.
  27. ^
    PMID 25207767
    .
  28. ^ "Pancreatic Cancer Treatment (PDQ®) Patient Version". National Cancer Institute. 2014-04-17. Retrieved 8 June 2014.
  29. PMID 23856911
    .
  30. PMID 18695761
    .
  31. ^
    ISBN 978-9283204299
    .
  32. ^ "American Cancer Society: Cancer Facts & Figures 2010: see page 4 for incidence estimates, and page 19 for survival percentages" (PDF). Archived from the original (PDF) on 2015-01-14.
  33. ^ "Pancreatic Cancer Treatment (PDQ®) Health Professional Version". NCI. 2014-02-21. Retrieved 8 June 2014.
  34. S2CID 7329783
    .
  35. PMID 18333264
    .
  36. ^
    OCLC 1076268769
    .
  37. ^ Davidson's 2018, p. 735.
  38. ^ Davidson's 2018, p. 730-732.
  39. ^ a b Davidson's 2018, p. 745-751.
  40. PMID 20567557
    .
  41. ISBN 978-1461505556
    .
  42. ISBN 978-8129118097
    .
  43. ^ Harper, Douglas. "Pancreas". Online Etymology Dictionary. Retrieved 2007-04-04.
  44. ISBN 978-0742547803
    .
  45. ^
    PMID 26788261
    .
  46. ^
    ISBN 978-0039102845
    .
  47. Oxford Companion to Food; Oxford English Dictionary
  48. ISBN 0747560463
    .

Bibliography

External links
Retrieved from "https://en.wikipedia.org/w/index.php?title=Pancreas&oldid=1217985136"