Islets of Langerhans ( Pancreas )

Islets of Langerhans. 

What does mean Islets of langerhans?

Endocrine cells of pancreas form groups of cells called Islets of Langerhans. There are four kinds of cells in islets of Langerhans which secrete hormones. 

(1) Alpha (x) cells: They are 20% and secrete glucagon. Glucagon is a hyperglycemic hormone. It stimulates the liver for glucogenolysis and increases the blood glucose level. 

 (2) Beta (B) cells: They are 70% and secrete insulin. Insulin is a hypoglycemic hormone. It stimulates liver and muscles for glycogenesis. This lowers blood glucose level. 

 3) Delta (8) cells: They are 5% and secrete somatostatin. Somatostatin inhibits the secretion of glucagon and insulin. It also decreases the gastric secretions, motility and absorption in the digestive tract. In general it is a growth inhibiting factor. 

 (4) PP cells or F cells: They form 5%. They secrete pancreatic polypeptide (PP) which inhibits the release of pancreatic juice

Histology of the Pancreas

The pancreas is made up of small clusters of glandular epithelial cells. About 99% of the clusters, called acini (AS-i-nı¯),constitute the exocrine portion of the organ .The cells within acini secrete a mixture of fluid and digestive

enzymes called pancreatic juice. The remaining 1% of the clusters, called pancreatic islets form the endocrine portion of the pancreas. These cells secrete the hormones glucagon, insulin, somatostatin, and pancreatic polypeptide. 

Composition and Functions of Pancreatic Juice : :

Each day the pancreas produces 1200–1500 mL (about 1.2–1.5 qt) of pancreatic juice, a clear, colorless liquid consisting mostly

of water, some salts, sodium bicarbonate, and several enzymes.

The sodium bicarbonate gives pancreatic juice a slightly alkaline pH (7.1–8.2) that buffers acidic gastric juice in chyme,stops the action of pepsin from the stomach, and creates the

proper pH for the action of digestive enzymes in the small intestine. The enzymes in pancreatic juice include a starch-digesting

enzyme called pancreatic amylase; several enzymes that digest

proteins into peptides called trypsin (TRIPsin),chymotrypsin,carboxypeptidase ,and elastase ; the principal triglyceridedigesting

enzyme in adults, called pancreatic lipase; and nucleic acid–digesting enzymes called ribonuclease and

deoxyribonucleas that digest

ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) into nucleotides.

The protein-digesting enzymes of the pancreas are produced

in an inactive form just as pepsin is produced in the stomach as pepsinogen. Because they are inactive, the enzymes do not digest cells of the pancreas itself. Trypsin is secreted in an inactive form called trypsinogen (trip-SIN-oˉ-jen). Pancreatic acinar

cells also secrete a protein called trypsin inhibitor that combines with any trypsin formed accidentally in the pancreas or in

pancreatic juice and blocks its enzymatic activity. When trypsinogen reaches the lumen of the small intestine, it encounters

an activating brush-border enzyme called enterokinase which splits off part of the trypsinogen molecule

to form trypsin. In turn, trypsin acts on the inactive precursors (called chymotrypsinogen, procarboxypeptidase, and proelastase) to produce chymotrypsin, carboxypeptidase, and elastase, respectively.