Difference between revisions of "Pancreas" - New World Encyclopedia

From New World Encyclopedia
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The '''pancreas''' is a pinkish white glandular organ found in vertebrates near the stomach and small intestine. It is one of the few organs that has both an endocrine and an exocrine function. Its exocrine function involves the secretion of bicarbonate and digestive [[enzyme]]s into the small intestine. Its endocrine function involves the regulation of blood sugar levels by secreting the hormones [[insulin]] , [[glucagon]] and [[somatostatin]] directly into the blood. Although the organ only weighs about 160 grams in the adult human being, it  secretes one to three liters of fluid per day.
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The '''pancreas''' is a pinkish white glandular organ found in vertebrates near the stomach and small intestine. It is one of the few organs that has both an endocrine and an exocrine function. Its exocrine function involves the secretion of bicarbonate and digestive [[enzyme]]s into the small intestine. Its endocrine function involves the regulation of blood sugar levels by secreting the hormones [[insulin]] , [[glucagon]] and [[somatostatin]] directly into the blood. The endocrine portion of this organ consists of about 1 million islets (Langerhans) amounting to only 2-3 percent of the organ weight, which is  about 160 grams in the adult human being. The majority of cells are exocrine and they secrete one to three liters of digestive fluid per day.
  
  
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===Exocrine function===
 
===Exocrine function===
  
There are two main classes of exocrine pancreatic secretions:
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There are two main types of exocrine pancreatic secretions: (1) the aqueous alkaline type and (2) the enzyme rich type.
  
 
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Revision as of 23:34, 19 May 2007

Pancreas
Illu pancrease.jpg
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
Vein Pancreaticoduodenal veins
Nerve Pancreatic plexus, celiac ganglia, vagus[1]
Precursor pancreatic buds

The pancreas is a pinkish white glandular organ found in vertebrates near the stomach and small intestine. It is one of the few organs that has both an endocrine and an exocrine function. Its exocrine function involves the secretion of bicarbonate and digestive enzymes into the small intestine. Its endocrine function involves the regulation of blood sugar levels by secreting the hormones insulin , glucagon and somatostatin directly into the blood. The endocrine portion of this organ consists of about 1 million islets (Langerhans) amounting to only 2-3 percent of the organ weight, which is about 160 grams in the adult human being. The majority of cells are exocrine and they secrete one to three liters of digestive fluid per day.


Anatomy

In adult human beings, the pancreas is a 6-10 inch elongated organ weighing about 160 grams and lying in the abdominal cavity . It lies posterior to the stomach, anterior to the kidneys and empties into the duodenum portion of the small intestine.

In people it has five regions: (1) the head,which touches the duodenum,(2) the body,which lies at the level of second lumbar vertebrae of the spine (3) The tail ,which extends towards the spleen,(4) the uncinate process and (5) the pancreatic notch,which is formed at the bend of the head and body

The pancreatic duct or duct of Wirsung runs the length of the pancreas and empties into the duodenum at the ampulla of Vater. The common bile duct usually joins the pancreatic duct at or near this point.

Many people also have a small accessory duct, the duct of Santorini, which extends from the main duct more upstream (towards the tail) to the duodenum, joining it more proximally than the ampulla of Vater.

Blood supply

The pancreas is supplied arterially by the pancreaticoduodenal arteries:

  • the superior mesenteric artery provides the inferior pancreaticoduodenal arteries
  • the gastroduodenal artery provides the superior pancreaticoduodenal artery

Venous drainage is via the pancreaticoduodenal veins which end up in the portal vein. The splenic vein passes posterior to the pancreas but is said to not drain the pancreas itself. The portal vein is formed by the union of the superior mesenteric vein and splenic vein posterior to the neck of the pancreas. In some people (some books say 40% of people), the inferior mesenteric vein also joins with the splenic vein behind the pancreas (in others it simply joins with the superior mesenteric vein instead).

Nerve supply

The pancreas receives neural innervation from the vagus (cranial X). This is part of the autonomic parasympathetic supply. The role of the vagus is to stimulate secretion of the pancreatic digestive juices.

Autonomic sympathetic nerves to the pancreas derive from the celiac ganglionic plexus and the superior mesenteric plexus. These plexi lie outside the pancreas and send postganglionic fibers into the pancreatic cells. The sympathetic nerves inhibit the production of digestive enzymes (Berne et al. 1996).

Microscopic anatomy

The microscopic appearance of the pancreas shows a series of islands (the Islets of Langerhans) consisting of small cells packed closely together ,surrounded by much larger and less dense acinar cells. The islands have an endocrine function and the surrounding cells have an exocrine function.


File:Pancreas.jpg
endocrine and exocrine pancreas

When the pancreas is sliced and stained and then viewed with a microscope, it is easy to distinguish many different types of cells that correspond to different pancreatic functions:

Appearance Region Function
centralized islands(islets of Langerhans) endocrine pancreas secretes hormones that regulate blood glucose levels
surrounding acinar cells exocrine pancreas produces enzymes that break down digestible foods

Function

Endocrine function

There are four main types of cells in the islets of Langerhans. They are relatively difficult to distinguish using standard staining techniques, but they can be classified by their secretion:

Name of cells Product % of islet cells Representative function
beta cells Insulin and Amylin 50-80% lower blood sugar
alpha cells Glucagon 15-20% raise blood sugar
delta cells Somatostatin 3-10% inhibit endocrine pancreas
PP cells Pancreatic polypeptide 1% inhibit exocrine pancreas

The islets are a compact collection of endocrine cells arranged in clusters and cords that are crisscrossed by a dense network of capillaries. The capillaries are lined by layers of endocrine cells in direct contact with them by either cytoplasmic processes or by direct apposition. The cells release their hormones,without ducts,directly into the capillaries.

The endocrine function of the pancreas is to produce important hormones including insulin, glucagon and somatostatin and export them to the blood supply on demand.

Exocrine function

There are two main types of exocrine pancreatic secretions: (1) the aqueous alkaline type and (2) the enzyme rich type.

Secretion Cell producing it Primary signal
bicarbonate ions Centroacinar cells Secretin
digestive enzymes (pancreatic amylase, trypsin, chymotrypsin, etc.) Basophilic cells CCK

Diseases of the pancreas

Due to the importance of its enzyme contents, injury to the pancreas is potentially very dangerous. A puncture of the pancreas generally requires prompt surgical intervention.

  • Diabetes mellitus
  • tumours both benign and cancerous
    • Carcinoma of the pancreas
    • Insulinoma
    • Glucagonoma
  • Cystic fibrosis
  • Exocrine pancreatic insufficiency
  • Hemosuccus pancreaticus, or bleeding from or through the pancreatic duct
  • Pancreatitis
  • Pancreatic pseudocyst

History

The pancreas was discovered by Herophilus (335-280 B.C.E.), 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,meaning "all", and kreas,meaning "flesh". [2]

Diabetes and the Pancreas

A new discovery might have important implications for treatment of diabetes. Researchers at the Toronto Hospital for Sick Children injected capsaicin into mice with type 1 diabetes , in an attempt to destroy the pancreatic sensory nerves. This treatment reduced the development of diabetes in these mice by 80%, suggesting a link between neuropeptides and the development of diabetes. When the researchers injected the pancreas of the diabetic mice with sensory neuropeptide (sP), they were cured overnight of diabetes for as long as 4 months. Also, insulin resistance (characteristic of type 2 diabetes) was reduced. These research results are in the process of being confirmed, and their applicability in humans will have to be established in the future.reference??


Additional images

References
ISBN links support NWE through referral fees

  • Berne,R.M. and M.N.Levy. 1996. Principles of Physiology,second edition,published by Mosby - Year Book,Inc.,St.Louis,MO.
  1. Physiology at MCG 6/6ch2/s6ch2_30
  2. Harper, Douglas. Pancreas. Online Etymology Dictionary. Retrieved April 4, 2007.

Template:Endocrine pancreas

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