PANCREATIC SECRETION

1. Lecture 5 Dr. Zahoor Ali Shaikh PANCREATIC SECRETION

2. PANCREATIC SECRETION • When food comes to small intestine [duodenum], it is mixed with pancreatic secretion and bile [pancreas and liver are accessory digestive organs]. PANCREAS • It is exocrine and endocrine secretion. • We will discuss exocrine secretion.

3. PANCREATIC SECRETION • Pancreas is elongated gland lies behind and below the stomach. • Pancreas has Acini and ducts. - Pancreatic Acinar cells secrete – digestive enzyme. - Pancreatic duct – secrete watery secretion rich in NaHCO3

4. COMPOSTION 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

6. PANCREATIC SECRETION • Exocrine Pancreas secretes pancreatic juice. • It has two components: 1. Pancreatic enzymes – secreted by Acinar cells. 2. Watery [aqueous] alkaline fluid rich in NaHCO3 actively secreted by duct cells that line the pancreatic ducts.

7. 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.

8. PANCREATIC SECRETION • 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. • We will discuss one by one.

9. PANCREATIC SECRETION (i). Pancreatic Proteolytic enzymes • Major Proteolytic enzymes are - Trypsinogen - Chymotrypsinogen - Procarboxypeptidase • They are secreted in INACTIVE form.

10. Pancreatic Proteolytic Enzymes • How these Proteolytic enzymes are activated? • 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.

11. Pancreatic Proteolytic Enzymes • Trypsin once formed activates Trypsinogen [autocatalytic] and also Chymotrypsinogen and Procarboxypeptidase. • They are converted to active form by Trypsin in duodenal lumen also. • IMPORTANT – We need initially Enterokinase to form trypsin. Once trypsin is formed it carries out other processes.

12. Pancreatic Proteolytic Enzymes

13. Pancreatic Proteolytic Enzymes • Proteolytic Enzymes [Trypsin, Chymotrypsin, Carboxypeptidase] attack different peptide linkages. • End result is formation of small peptide chains and amino acids.

14. (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.

15. (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.

16. (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.

17. Clinical Application 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].

18. Pancreatic Insufficiency • Up to 60 – 70% of fat taken maybe excreted in feces in STEATORRHEA. • Digestion of protein and carbohydrate is impaired to a lesser degree because salivary, gastric and small intestine enzymes contribute to their digestion.

19. 2. 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? - Because 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.

20. Regulation Or Control Of Pancreatic Exocrine Secretion • It is hormonal and neural mechanism. 1. Mainly by hormonal mechanism – secretin and Cholecystokinin [CCK]. 2. Parasympathetic stimulation – little contributionduring cephalic phase.

21. Regulation Or Control Of Pancreatic Exocrine Secretion [cont] • When Chyme enters the duodenum, Two major hormones secretin and CCK [Entrogastrones] are released in response to Chyme.

23. Regulation Or Control Of Pancreatic Exocrine Secretion • We will discuss 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 NaHCO3 rich watery secretion in the duodenum. • NaHCO3 neutralizes the acid content of Chyme.

24. 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.

25. Regulation Or Control Of Pancreatic Exocrine Secretion CHOLECYSTOKININ [CCK] (cont) • 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.

26. What You Should Know From This Lecture • Pancreatic Exocrine Secretion • Composition • Pancreatic Enzymes & Their Importance • Steatorrhea • Mechanism of Pancreatic Juice Secretion • Regulation of Pancreatic Exocrine Secretion - Hormonal & Neural

27. Thank you