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Pancreas

Pancreas is a retroperitonial organ that extends obliquely from the structure that lies in the epigastrium and the left upper quadrant. It is soft, lobulated and situated on the posterior abdominal wall behind the peritoneum. It is 12-15 cm in length and weighs about 85 grams. Head is disc-shaped and lies within the concavity of duodenum. Posteriorly it arises from the 12th thoracic vertebra, and then on the 1st lumbar vertebrae. A part of it extends to the left behind the superior mesenteric vessel called uncinate process.

Neck: is constricted portion which connects head to the body. It lies in front of the beginning of the portal vein and origin of the superior mesenteric artery from aorta.
Body: runs upward and to the left, crosses the midline.
Tail: passes forward in leinorenal ligament and comes in contact with the splenic hilum.

Anteriorly: it is related with transverse colon and attachment of transverse mesocolon, lesser sac and omentum.
Posteriorly: with bile duct, portal and splenic vein, aorta origin of superior mesenteric artery, left suprarenal glands, left kidney and hilum of spleen.

The pancreatic duct:
The pancreatic duct begins in the tail, runs through the whole length of the gland and opens in the second part of the duodenum and eventually joins the bile duct at Ampulla of Vater.

The accessory duct:
drains the upper part of the head and then opens into duodenum a short distance above the main duct. It frequently communicates with the main duct.

Blood supply:
is from the splenic artery, superior and inferior pancreaticoduodenal arteries.

Venous drainage:
drain in to the portal system.

Lymph drainage:
into the lymphatic nodes situated along the arteries then drain into celiac and superior mesenteric nodes.

Nerve supply:
is from sympathetic and parasympathetic vagal nerve fibers.

Physiology:


Cells:
Basically there are three types of cells:
Acinar cells:
The acinar cells line the acini of the pancreas and are responsible for the external excretion of the pancreas that is ejected out through the pancreatic ducts.

Islet cells:
Islet cells are arranged in islets or clumps called the Islets of Langerhann and are responsible for the internal secretions. These cells are three types:
  • Alpha cells: The alpha cells secrete glucagon, which has a hyperglycemic (anti insulin) action
  • Beta cells: These cells secrete insulin
  • Non-beta cells: These cells secrete a substance that is pharmacologically identical to that of gastrin. If a tumor arises in these cells, it causes fulminating peptic ulcers (Zollinger-Ellision syndrome)
External secretions:
A normal person (adult) secretes about one litre of pancreatic juice daily. This juice is highly alkaline in nature because of high sodium bicarbonate content and contains digestive enzymes, which act on starch, fat and proteins:
  • Amylase (diastase): for the carbohydrate digestion
  • Lipase: for fat digestion
  • Trypsinogen: for protein digestion. Trypsinogen, as such, is inactive. It must be converted to its active form called trypsin, which normally done by succus entericus. It is believed that trypsinogen may also be converted to trypsin by bile, by the tissue juices and by products of the bacterial growth. Chymotrypsin is another proteolytic enzyme secreted by pancreas


Control of secretions:
The external secretions of pancreas are controlled by the humoral and nervous mechanisms, of which latter is of less significant.
  • Humoral: this involves two hormones, both of which are liberated in the mucosa of the duodenum and upper jejunum, chiefly by the action of the acids and also by food. They are carried by blood to the pancreas. The hormones are:
    • Secretin: this produces large amount of secretions, rich in sodium and bicarbonates but poor in enzymes
    • Pancreozymin: it produces small amount of viscid secretions but rich in enzymes
  • Nervous: initiated by vagal stimulation. The secretions is small, viscid and rich in enzymes
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This article has been written by Dr. M. Javed Abbas.
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12:00 08/02/2003