Pancreatic Secretions Pancreatic Exocrine Secretion February 22, 2019 Pancreatic Secretions

Pancreatic Secretions Pancreatic Cell Types Contains endocrine, exocrine and ductal cells Endocrine cells Arranged in small islets Secrete insulin, Glucagon, Somatostatin and pancreatic polypeptides February 22, 2019 Pancreatic Secretions

Pancreatic Secretions Pancreatic Cell Types The exocrine cells Organized into acini produce digestive enzymes Peptidases digest proteins Lipases digest fat Amylase digest carbohydrates Nuclease digest nucleic acids February 22, 2019 Pancreatic Secretions

Pancreatic Secretions Acinar cells with zymogen granules Intercalated Duct February 22, 2019 Pancreatic Secretions

Composition of Pancreatic Secretion EXOCRINE Water Electrolytes Na+, K+ ( concentration same as in plasma) HCO3- conc much higher than in plasma 100mEq/L (cf 24 mEq/L) Cl-, Ca++, Mg++ February 22, 2019 Pancreatic Secretions

Composition of Pancreatic Secretion Digestive enzymes Pancreatic α amylase For digestion of carbohydrate Pancreatic Lipase For lipid hydrolysis February 22, 2019 Pancreatic Secretions

Composition of Pancreatic Secretion Proteolytic enzymes Produced in an inactive form (pro-enzymes) Trypsinogen, Chemotrypsinogen Pro-carboxy peptidases Elastase, Ribonuclease Deoxyribonuclease February 22, 2019 Pancreatic Secretions

Mechanism of Secretion Water and electrolyte Pancreatic juice Iso osmolar with plasma Ionic content varies with rate of secretion N+ and K+ do not vary Approx equal to that of plasma At increased rate Cl- falls HCO3- rises February 22, 2019 Pancreatic Secretions

Pancreatic Secretions RELATIONSHIP BETWEEN ELECTROLYTE CONCENTRATION IN PANCREATIC JUICE AND THE VOLUME SECRETED Pancreatic juice Na+ Plasma Na+ 150 HCO3 - Cl- 100 Concentration (meq/L) 50 Cl- HCO3 - K+ K+ 0.5 1.0 Secretory rate (ml/min) February 22, 2019 Pancreatic Secretions

Mechanism of Secretion CO2 diffuses into the cell CO2 + H2O  H2CO3  H+ + HCO3- Carbonic anhydrase H+ actively transported into blood in exchange with Na+ HCO3- transported into lumen of duct Acidification of plasma in the process of pancreatic juice secretion February 22, 2019 Pancreatic Secretions

Mechanism of Secretion HCO3-, Na+, K+, Cl- move into lumen Creates osmotic gradient H2O moves into duct by osmosis February 22, 2019 Pancreatic Secretions

Mechanism of Secretion As pancreatic juice flows along the duct Cl- is exchanged for HCO3- HCO3- is higher when the rate of secretion is higher February 22, 2019 Pancreatic Secretions

Mechanism of Secretion CO2 CO2 + H2O CA H2CO3 H+ H+ HCO3- HCO3- Duct lumen Na+ Na+ Blood Na+ Na+ K+ K+ K+ Cl- Cl- Cl- H2O H2O H2O February 22, 2019 Pancreatic Secretions

Pancreatic Secretions Secretion of Enzymes Acinar cells produce enzymes Pancreatic  - amylase Secreted in the active form Hydrolyses starch, glycogen Disaccharides Pancreatic Lipases (lipase, cholesterol lipase, phospholipase) Bile salt required to Hydrolyze water insoluble esters February 22, 2019 Pancreatic Secretions

Pancreatic Secretions Secretion of Enzymes Pancreatic proteases Trypsin, chemotrypsin Secreted in inactive form Trypsinogen Activated by trypsin Enterokinases Chymotrypsinogen February 22, 2019 Pancreatic Secretions

Pancreatic Secretions Secretion of Enzymes Trypsin inhibitor Produced by the same cells that produce the proenzymes Prevents activation of trypsinogen inside and out side the cell Prevent autodigestion of pancreas February 22, 2019 Pancreatic Secretions

Regulation of Secretion Three basic stimuli for secretion of pancreatic juice Acetylcholine (Ach) Released by nerve endings of vagus Other cholinergic nerve endings Enteric nerve endings February 22, 2019 Pancreatic Secretions

Regulation of Secretion Cholecystokinin (CCK) Secreted by cells of duodenum & upper jejunum Secretin Secreted from the duodenum In response to presence of acidic chyme February 22, 2019 Pancreatic Secretions

Regulation of Secretion Ach & CCK Stimulate acinar cells of pancreas Cause production of large quantities of enzymes Secretin Stimulate duct cells Produce large quantities of sodium bicarbonate February 22, 2019 Pancreatic Secretions

Pancreatic Secretions Cephalic Phase Higher centers Cephalic phase Sight, thought, smell ,taste of food Stimulation of parasympathetic Vagal impulses are transmitted to pancreas acinar and duct cells Sight, smell, thought taste Vagus Ach Acini cells Ach Enzymes February 22, 2019 Pancreatic Secretions

Pancreatic Secretions Cephalic Phase Higher centers Moderate amount of enzymes secreted (20% of total enzymes) Stimulated by enteric neurons use Ach Small amount of water and electrolyte HCO3- secretion stimulated by enteric neurons – use VIP Sight, smell, thought taste Vagus Ach Acini cells Ach Enzymes February 22, 2019 Pancreatic Secretions

Pancreatic Secretions Gastric Phase Vagal center Gastric phase Presence of food in the stomach Vago-vagal reflex Small volume of both HCO3- and enzymes secreted Ach as the transmitter Vagus Food Ach Gastrin Ach Enzymes & HCO3 - February 22, 2019 Pancreatic Secretions

Pancreatic Secretions Gastric Phase Vagal center Stimulation of G cells Produce Gastrin Causes secretion of low volume; high enzyme pancreatic juice Vagus Food Ach Gastrin Ach Enzymes & HCO3 - February 22, 2019 Pancreatic Secretions

Pancreatic Secretions Intestinal Phase Presence of food in duodenum Peptides, AA, Fat CCK released Cause large quantity of enzyme secretion Action of CCK are potentiated by Secretin CCK Secretin February 22, 2019 Pancreatic Secretions

Pancreatic Secretions Intestinal Phase Presence of acid chyme in duodenum Secretin released Copious amount of pancreatic juice high in HCO3- (145 mEq/L) low chloride Secretin effects are potentiated by CCK CCK Secretin February 22, 2019 Pancreatic Secretions

Regulatory Peptides & Pancreatic Secretion INHIBITION OF SECRETION: STIMULATION OF SECRETION SOMATOSTATIN (SS) PANCREATIC POLYPEPTIDE (PP) CALCITONIN GLUCAGON THYROID-RELEASING HORMONE HORMONE (TRH) CCK SECRETIN GASTRIN BOMBESIN Substance P VIP February 22, 2019 Pancreatic Secretions