Sunday, 8 February 2015

PANCREAS OF HUMAN DIGENSTIVE SYSTEM (DUAL GLAND): Location, structure. anatomical aspects, functions & disorders.

The pancreas is critically important for intestinal digestion. It is a large exocrine gland, synthesizing and secreting the great majority of digestive enzymes into the intestine. It also contains important endocrine tissue producing insulin and glucagons, thus also regulating nutrition and gastrointestinal function globally.


The pancreas lies transversely on the posterior abdominal wall and is covered by peritoneum. The head lies to the right, adjacent to the duodenum, and the body and tailextend across the epigastrium to the spleen. The splenic veinruns along the superior border of the pancreas and loops of intestine are related to it anteriorly. Branches of the coeliac and superior mesenteric arteries supply the gland and venous blood drains into the hepatic portal vein, supplying the liver with hormone- and growth factor-laden blood from the pancreas.
The vagus nerve and splanchnic sympathetic nerves innervate the pancreas. Sensory nerves are routed through the coeliac ganglion and pancreatic pain may be relieved by its surgical removal or destruction. The main pancreatic duct extends along the length of the gland and a smaller accessory duct drains the superior part of the head and may open separately into the duodenum. The main duct joins the common bile ductbefore opening into the duodenum through the ampulla of Vater. Smaller pancreatic ducts drain into the main duct, forming a ‘fishbone’ pattern.
Exocrine pancreatic tissue is arranged in lobules composed of the functional units, acini, which secrete pancreatic enzymes and fluid into the ducts. Microscopically, pancreatic cells are arranged in spherical acini, with their secretory or apical surface towards the centre and the basolateral surface resting on a basement membrane. Ductules drain each acinus and coalesce to form larger ducts that eventually drain into the main pancreatic duct, carrying digestive juices to the duodenum. Pancreatic acinar cells are highly specialized for protein synthesis and secretion. They have a pyramidal cross-section, with prominent basal rough endoplasmic reticulum, where protein synthesis occurs, extensive golgi apparatus and apical secretory (zymogen) granules. Over 106endocrine pancreatic is letsare scattered throughout the pancreas and are supplied with a rich capillary network of blood vessels.
They are not connected by ducts to the exocrine pancreas, but secrete directly into the bloodstream. The principle cells in these islets are b cells, which secrete insulin, a cells, that secrete glucagon, and D cells, which synthesize somatostatin.
Function The pancreas is a powerful producer of digestive enzymes. These are synthesized and stored as inactive precursors or pro-enzymes, to avoid auto digestion of the enzyme-producing cells and the pancreatic ducts.

Pancreatic enzymes include:
• trypsinogen;
• chymotrypsinogen;
• procarboxypeptidases Aand B;
• pro-elastase;
• phospholipase A;
• pancreatic lipase (and colipase);
• pancreatic amylase;
• ribonucleases;
• deoxyribonucleases.

Pancreatic secretion is stimulated by hormonal signals, particularly cholecystokinin, which is released when food enters the duodenum. Secretinenhances the effect of cholecystokinin. The pancreas secretes about 2L/dayof a bicarbonate-rich alkaline fluid that helps to neutralize stomach acid and provides optimal conditions for digestion by pancreatic enzymes. Centroacinar and duct cells secrete most of the fluid and alkali, by exchanging HCO3- for Cl- ions, using the cystic fibrosis transmembrane regulator (CFTR) protein. Pancreatic insufficiency therefore occurs in cystic fibrosis, where an abnormal CFTRgene is inherited. Pancreatic islets are the only source of insulin and glucagon, which are produced by pancreatic band acells, respectively. Insulin secretion is stimulated mainly by increased blood glucose, while glucagon secretion is stimulated by hypoglycaemia. Hormones, such as adrenaline, have additional modulatory effects on pancreatic islet secretion and islets also produce hormones, such as somatostatin, which modifies entero-endocrine function locally and throughout the gastrointestinal tract.

Common disorders 

Pancreatic diseases may remain entirely asymptomatic until they are far advanced. They may cause abdominal pain, felt in the epigastrium and radiating to the back.
Damage to the common pancreatic and bile ducts may cause jaundice and pancreatic exocrine insufficiency may result in mal absorption of food, causing diarrhoea, steatorrhoea (fat-rich stools), weight loss and nutritional deficiencies. Islet damage can cause diabetes mellitus. Acute pancreatitis is a serious, potentially life-threatening illness. The most common causes are excess alcohol ingestion and passage of gallstones through the ampulla of Vater. Less frequent causes include various drugs, abdominal trauma and viral infection. The inflamed pancreas releases enzymes into the circulation and acute pancreatitis is a systemic illness, affecting the whole body.
Pancreatic lipases release fatty acids that interact with calcium to form insoluble calcium-fatty acyl salts, potentially lowering the concentration of calcium in the circulation to dangerous levels. Adramatic rise in the serum lipase oramylase levelhelps to diagnose acute pancreatitis. Chronic pancreatitis may follow repeated bouts of acute pancreatitis. The main symptoms are abdominal pain and mal absorption due to failure of the exocrine pancreas. Patients may also develop endocrine pancreatic insufficiency.
Pancreatic adenocarcinoma is a leading cause of cancer-related death and often becomes symptomatic only at an advanced stage, when the tumour has become inoperable. Neuro-endocrine tumours, which arise from enteric endocrine cells, are often located in the pancreas, although they may also arise from other parts of the gastrointestinal tract. They are generally less aggressive than adenocarcinoma, but may cause symptoms due to their secretion of gut hormones. Gastrin-producing tumours (gastrinomas) cause excess gastric acid secretion and peptic ulceration (Zollinger–Ellison syndrome). Tumours may also secrete insulin, glucagon and other hormones.


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