PANCREAS

Location: The head of the pancreas lies in the curve of duodenum, the body crosses the midline of the body, and the tail extends towards the hilum of the spleen.

Composition:

The exocrine component is a compound gland with branched ducts and serous secretory units of acinar or tubuloacinar shape. It synthesizes and secretes, into the duodenum, enzymes that are essential in digestion in the intestine.
The endocrine component synthesizes and secretes, into the blood, insulin and glucagon, hormones that regulate glucose, lipid, and protein metabolism in the whole body. It is dispersed within exocrine component as distinct cell masses - islets of Langerhans.
The capsule, septa and stroma of loose connective tissue with ducts, blood vessels and nerve fibers surround the parenchymal units - lobules.

EXOCRINE PANCREAS

Function: secretion of enzymes:

Tripsinogen, pepsinogen, and carboxypeptidase - digest proteins.
Amylase - digests carbohydrates.
Lipase - digests lipids.
Deoxyribonuclease and ribonuclease - digest nucleic acids.

Composition: epithelium of pyramidal serous acinar cells rich of acidophilic zymogen granules with inactive enzymes or proenzymes.

DUCTS

Composition:

Centroacinar cells - the beginning of the duct system - the squamous epithelial cells within the acinus.

Intercalated duct is short and lies outside the acinus.

Function: secretion of large volume of fluid rich in sodium and bicarbonate.

Intralobular ducts constitute branching network within the lobules.

Interlobular ducts are lined by low columnar epithelium with occasional goblet cells and enteroendicrine cells.

Main pancreatic duct (duct of Wirsung) extends through the length of the gland and empties into duodenum at the ampulla of Vater after joining with common bile duct.

Accessory pancreatic duct (ductus choledochus) arises in the head of the pancreas.

ENDOCRINE PANCREAS

Location: islets of Langerhans are scattered throughout the pancreas, constitute about 1-2% of the volume, and are most numerous in the tail.

Composition and function: polygonal endocrine cells are arranged in short, irregular cords that are profusely invested with a network of fenestrated capillaries.

B cells - about 70% of the total cells, contain numerous secretory granules of about 300-nm diameter.

Function: secrete insulin that lowers blood glucose. Its principal effects are on liver, skeletal muscle, and adipose tissue. Insulin stimulates uptake of glucose from circulation, utilization and storage of glucose by all cells, phosphorylation of glucose and synthesis of glycogen.

A cells - about 15-20 % of the total cells, contain secretory granules of about 250-nm diameter.

Function: secrete glucagon. It stimulates: release of glucose into the bloodstream, gluconeogenesis and glycogenolysis in the liver, proteolysis, lipolysis.

D cells - about 5-10% of the total cells, contain secretory granules of about 300-350-nm diameter.

Function: secrete somatostatin. It is identical to hypothalamic hormone that regulate somatotropin release from anterior pituitary gland. It inhibits both insulin and glucagon secretion.

Minor cell types - about 5% of total cells.

PP (F) cells secrete Pancreatic polypeptide, that stimulates gastric chief cells, inhibits bile and pancreatic secretion, and intestinal motility.

D-1 cells secrete Vasoactive intestinal peptide (VIP) that actions are similar to those of glucagon, and stimulates pancreatic exocrine secretion.

EC cells (enterochromaffin cells) secrete secretin (stimulates bicarbonate and pancreatic enzyme secretion), motilin (increases gastric and intestinal motility) and substance P (?).