Presentation on theme: "Lecture 5 Dr. Zahoor Ali Shaikh"— Presentation transcript:
1 Lecture 5 Dr. Zahoor Ali Shaikh PANCREATIC SECRETIONLecture 5Dr. Zahoor Ali Shaikh
2 PANCREATIC SECRETIONWhen food comes to small intestine [duodenum], it is mixed with pancreatic secretion and bile [pancreas and liver are accessory digestive organs].PANCREASIt is exocrine and endocrine secretion.We will discuss exocrine secretion.
3 PANCREATIC SECRETIONPancreas is elongated gland lies behind and below the stomach.Pancreas has Acini and ducts.- Pancreatic Acinar cells secrete – digestiveenzyme.- Pancreatic duct – secrete watery secretionrich in NaHCO3
4 COMPOSTION OF PANCREATIC JUICE Pancreatic secretion per day is 1 – 2 liters.pH – approximately 8.0It 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 SECRETIONPancreas 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.
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.
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 Pancreatic insufficiency Clinical ApplicationPancreatic insufficiencyWhen 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 contribution during 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.SECRETINPrimary 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 SecretionCompositionPancreatic Enzymes & Their ImportanceSteatorrheaMechanism of Pancreatic Juice SecretionRegulation of Pancreatic Exocrine Secretion -Hormonal & Neural