Pancreas Exocrine Pancreas - racemose Endocrine Pancreas- islets of Langerhans

Exocrine Pancreas Secretory units – acini - pyramidal cells surrounding the central lumen. Lumen of the acini –main pancreatic duct or Duct of Wirsung Accessory pancreatic duct – Duct of Santorini Duct of Wirsung joins with common bile duct & enters the II part of duodenum through papilla of Vater guarded by Sphincter of Oddi Innervated by Vagus nerve

Pancreatic juice Pancreatic juice is a watery,colorless fluid Quantity L in 24 hrs pH Sp.gravity Pancreatic juice 98.5%water 1.5% solids organic inorganic enzymes cations anions

Organic constituents Enzymes. (Secreted by acinar cells) Proteolytic : Trypsinogen Chymotrypsinogen Procarboxypeptidase A & B Proelastase Ribonuclease Deoxy ribonuclease

Lipolytic Enzymes Pancreatic lipase Colipase Phospholipase Amylolytic Enzyme Pancreatic alpha amylase Trypsin inhibitor Prevents activation of enzymes inside the pancreas Protects pancreas from autodigestion

Inorganic constituents Cations Na + K + Ca 2+ Mg 2+ Anions HCO 3- Cl - SO 4 2-

Formation of Pancreatic juice Enzymes - acinar cells Bicarbonate & other electrolytes – cells lining the ducts centroacinar cells (junction of the acini with the duct)

MECHANISM OF BICARBONATE SECRETION

Activation of enzymes Trypsinogen  Enterokinase Trypsin Trypsin converts the precursors into their respective active forms Chymotrypsinogen  Chymotrypsin Procarboxypeptidase  Carboxypeptidase Proelastase  Elastase

Functions Proteolytic enzymes Trypsin & Chymotrypsin Secreted as inactive proenzymes Converted to active enzymes by trypsin Trypsin & chymotrypsin are endopeptidases Hydrolyse proteins into peptides

Carboxypeptidase proteins/ peptides  aminoacids Ribonuclease & deoxyribonuclease nucleoprotein  nucleotides Elastase Acts on elastin

Amylolytic enzyme Pancreatic Amylase Acts on Starch (cooked & uncooked) Converts into maltose, maltotriose and dextrins

Lipolytic Enzymes Pancreas is the only effective source for lipolytic enzyme Pancreatic lipase Fats  fattyacids and monoglyceride Colipase - anchors lipase to fat droplet Phospholipase - phospholipids  lysophospholipids & fattyacids

Phases of Secretion Cephalic Phase Gastric phase Intestinal Phase

Cephalic Phase Contributes to about 15-20% of secretion Sight, smell, thought (conditioned reflex) Presence of food in mouth (unconditioned reflex) Nervous Regulation : Vagal stimulation - Pancreatic secretion rich in enzymes. Acetylcholine - neurotransmitter

Gastric Phase Contributes to about 5-10% of secretion Both neural & hormonal Neural Mechanism Presence of food in the stomach (distension)  Vagal stimulation (Gastropancreatic reflex)  Secretion of pancreatic juice

Hormonal Mechanism in Gastric phase Chemical excitation of the S cells of the small intestine by the acid in the gastric juice releases Secretin  Acts on ductal cells  Secretion of pancreatic juice rich in fluids and bicarbonate

Intestinal Phase Contributes to about 75% of secretion Mainly hormonal Chemical excitation of the S cells of the small intestine by the acid in the gastric juice releases Secretin  Acts on ductal cells  Secretion of pancreatic juice rich in fluids and bicarbonate

Chemical excitation of the I cells of the small intestine by the partially digested proteins & fatty acids in the gastric juice releases CCK-PZ  Acts on acinar cells  Secretion of pancreatic juice rich in enzymes

First Hormone to be discovered (Hormone –Excite ) Discovered by Bayliss & Starling in 1902 Produced by S cells of small intestine Stimuli for secretion -Acid in duodenum Aminoacids & Fattyacids Actions -On ductal cells to release watery juice rich in Bicarbonate Potentiates the effect of CCK Stimulates bile secretion Delays Gastric emptying Secretin

Feed back control of secretion of Secretin Acid in duodenum  Secretin  Alkaline Pancreatic juice  Neutralises Acid  Inhibits Secretin

CCK-PZ Cholecystokinin pancreozymin Acts on Acinar cell Releases pancreatic juice rich in enzymes Stimuli for release -Aminoacids Fattyacids Produced by I cells of Small intestine

Actions of CCK-PZ Stimulates secretion of pancreatic juice rich in enzymes Causes contraction of Gallbladder Potentiates the effect of Secretin Increase the secretion of Enterokinase Produces trophic effect on pancreas Found in the brain & involved in regulation of food intake

Applied Physiology Acute pancreatitis Auto digestion of pancreas Serum amylase  Congenital Fibrocystic Disease - Genetic Defect Fibrous tissue++ in the pancreas Fibrosis of lung Complete extirpation of Pancreas (For carcinoma) Diabetes Mellitus, Steatorrhoea

Steatorrhoea Causes - Destruction of exocrine pancreas Gall stone blocking pancreatic duct Defective absorption of Bile salts in Ileum Features - Pale, Bulky, Greasy, Foul smelling stools Faecal fat - Normal Fat Content. 5-6gms/day Steatorrhoea gms/day

Pancreatic Function tests Serum Amylase- Increased in acute pancreatitis Secretin CCK-PZ test. When CCK-PZ & Secretin injected-  In Bicarbonate,Fluids & enzymes. Chronic pancreatic insufficiency-Weak response Fecal fat Estimation- Normal 5-6gms/day Steatorrhoea-40-50gms/day Pancreatic enzymes given in chronic pancreatic insufficiency

OUT COME Describe composition and function of pancreatic juice Describe mechanism of bicarbonate ion secreation Describe regulation of pancreatic juice secretion