Everything about The Pancreas totally explained
The
pancreas is a
gland organ in the
digestive and
endocrine system of vertebrates. It is both
exocrine (secreting
pancreatic juice containing
digestive enzymes) and
endocrine (producing several important
hormones, including
insulin,
glucagon, and
somatostatin).
Histology
Under a microscope, stained sections of the pancreas reveal two different types of
parenchymal tissue. 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.
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 a million cell clusters called
islets of Langerhans. There are four main cell types 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, β cells secrete
insulin, δ cells secrete
somatostatin, and PP cells secrete
pancreatic polypeptide.
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, 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, and secretes them into the
small intestine through a system of
exocrine ducts. 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.
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.
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.
History
The pancreas was first identified 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 pan, "all", and
kreas, "flesh", probably referring to the organ's homogeneous appearance.
As food
Pancreases (specifically calf and lamb pancreases) are eaten in meals like
sweetbread, often going by the name stomach.
Embryological development
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.
Differential rotation and fusion of the ventral and dorsal pancreatic buds results in the formation of the definitive pancreas. 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.
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.
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-6, forms α- and γ- cells, which produce the peptides
glucagon and
pancreatic polypeptide, respectively. The second line, influenced by
Pax-4, produces β- and δ-cells, which secrete
insulin and
somatostatin, respectively.
Insulin and glucagon can be detected in the fetal circulation by the fourth of fifth month of fetal development.
Additional images
Image:Digestive system showing bile duct.png|Accessory digestive system.
Image:BauchOrgane wn.png|Digestive organs.
Image:Gray533.png|The celiac artery and its branches; the stomach has been raised and the peritoneum removed.
Image:Gray614.png|Lymphatics of stomach, etc. The stomach has been turned upward.
Image:Gray1097.png|Transverse section through the middle of the first lumbar vertebra, showing the relations of the pancreas.
Image:Gray1098.png|The duodenum and pancreas.
Image:Gray1100.png|The pancreatic duct.
Image:Gray1101.png|Pancreas of a human embryo of five weeks.
Image:Gray1102.png|Pancreas of a human embryo at end of sixth week.
Image:Gray1225.png|Front of abdomen, showing surface markings for duodenum, pancreas, and kidneys.
Further Information
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