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PANCREATIC SECRETION

PANCREATIC SECRETION. DR. AMEL EASSAWI Dr. Shaikh Mujeeb Ahmed. OBJECTIVES. The student should be able to: Discuss pancreatic exocrine secretion and composition. Enlist pancreatic enzymes and their importance Describe Steatorrhea . Explain the mechanism of pancreatic juice secretion.

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PANCREATIC SECRETION

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  1. PANCREATIC SECRETION DR. AMEL EASSAWI Dr. ShaikhMujeeb Ahmed

  2. OBJECTIVES The student should be able to: • Discuss pancreatic exocrine secretion and composition. • Enlist pancreatic enzymes and their importance • Describe Steatorrhea. • Explain the mechanism of pancreatic juice secretion. • Describe the regulation of pancreatic exocrine secretionhormonal and neural.

  3. PANCREATIC SECRETION • When food enter the small intestine [duodenum], it is mixed with pancreatic secretion and bile [pancreas and liver are accessory digestive organs]. • Pancreas is elongated gland lies behind and below the stomach. • Has exocrine and endocrine secretion. • Exocrine Pancreas secretes pancreatic juice. • Pancreas has Acini and ducts. - Pancreatic Acinar cells secrete – digestive enzyme. - Pancreatic duct – Watery [aqueous] alkaline fluid rich in NaHCO3

  4. PANCREATIC SECRETION Composition of Pancreatic Juice • Pancreatic secretion per day is 1 – 2 liters. • pH – approximately 8.0 • It has - Water - Cations – Na, K, Ca, Mg - Anions – HCO3, Cl, SO4, HPO4 - Digestive enzymes

  5. PANCREATIC SECRETION 1. Pancreatic Enzymes • The pancreatic enzymes are stored in zymogen granules after they are produced. • They are released by exocytosis as needed. • Pancreatic enzymes are important because they can completely digest food, in absence of all other digestive secretions. Pancreas Acinar Cell Secrete Three Types of Pancreatic Enzymes: i. Proteolytic enzymes for protein digestion. ii. Pancreatic amylase for carbohydrate digestion. iii. Pancreatic Lipase for fat digestion.

  6. PANCREATIC SECRETION (i). Pancreatic Proteolytic Enzymes • Major Proteolytic Enzymes are: - Trypsinogen - Chymotrypsinogen - Procarboxypeptidase • They are secreted in inactive form. • Proteolytic Enzymes [Trypsin, Chymotrypsinogen, Carboxypeptidase] attack different peptide linkages. • End result is formation of small peptide chains and amino acids.

  7. PANCREATIC SECRETION Activation of Pancreatic Proteolytic Enzymes • When Trypsinogen is secreted into the duodenal lumen, it is activated to its active form Trypsin by Enterokinase [enteropeptidase], an enzyme which is embedded in the mucus membrane of duodenal mucosa. • Trypsin once formed activates more Trypsinogen [autocatalytic]. • Chymotrypsinogen and Procarboxypeptidase are converted to active form by Trypsin in duodenal lumen. • IMPORTANT – We need initially Enterokinase to form trypsin. Once trypsin is formed it carries out other processes.

  8. Pancreatic Proteolytic Enzymes

  9. PANCREATIC SECRETION (ii). Pancreatic Amylase for Carbohydrate Digestion • Pancreatic amylase causes conversion of polysaccharides into disaccharide maltose. • Pancreatic amylase is secreted in the Active form as it is not the risk for auto digestion of pancreas. (iii).Pancreatic Lipase for Fat Digestion • Pancreatic lipase is very important. Why? • Because it is the only enzyme secreted throughout the digestive system that can digest fat. • NOTE : In human, insignificant amount of lipase are secreted in the saliva and Gastric Juice called Lingual Lipase and Gastric Lipase.

  10. PANCREATIC SECRETION (iii).Pancreatic Lipase for Fat Digestion • Pancreatic lipase hydrolysis dietary triglycerides into Monoglyceride and Free fatty acids, which are absorbed in small intestine. • Pancreatic lipase is secreted in Active form as it is not the risk for pancreatic auto-digestion.

  11. PANCREATIC SECRETION Pancreatic Aqueous Alkaline Fluid • As highly acidic Gastric contents are emptied into the duodenal lumen, this acidic Chyme must be neutralized quickly in the duodenal lumen.Why? - To allow the functioning of pancreatic enzymes [they work in neutral or slightly alkaline medium]. NaHCO3 in pancreatic fluid neutralizes the acidic Chyme. - To prevent damage to duodenal mucosa.

  12. Regulation Or Control Of Pancreatic Exocrine Secretion Hormonal and Neural Mechanism: • Mainly by hormonal mechanism: Secretin and Cholecystokinin [CCK]. 2. Parasympathetic stimulation: little contributionduring cephalic phase. • When Chyme enters the duodenum, Two major hormones secretin and CCK [Entrogastrones] are released in response to Chyme.

  13. Regulation Or Control Of Pancreatic Exocrine Secretion Role of secretin and CCK. SECRETIN • Primary stimulus for secretion of secretin is acid in the duodenum. • Secretin is carried by blood to the pancreas where it stimulates the duct cells to increase NaHCO3rich watery secretion in the duodenum. • NaHCO3 neutralizes the acid content of Chyme.

  14. Regulation Or Control Of Pancreatic Exocrine Secretion CHOLECYSTOKININ [CCK] • CCK is released from duodenal mucosa. • Main stimulus for release of CCK is Fat, to a lesser extent protein. • CCK is transported by blood to pancreas Acinar cell to increase digestive enzyme secretion. • These pancreatic enzymes help to digest fat, protein and carbohydrate. • All three types of enzymes [for protein, fat, and carbohydrate] are packed in Zymogen granules together, therefore, all are released together by exocytosis.

  15. Clinical Application 1. Pancreatic Insufficiency • When pancreatic enzymes are deficient, digestion of food is incomplete. • As pancreatic lipase is the only significant source for fat digestion, its deficiency results in Maldigestion of fats, it is called STEATORRHEA [increased undigested fat in feces. • Up to 60 – 70% of fat taken maybe excreted in feces. • Digestion of protein and carbohydrate is impaired to a lesser degree because salivary, gastric and small intestine enzymes contribute to their digestion.

  16. References • Human Physiology by Lauralee Sherwood, seventh edition. • Text book Physiology by Guyton &Hall,11th edition. • Text book of Physiology by Linda S. Contanzo, third edition.

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