L2 Role of Salivary Glands and Stomach Digestion PDF

L2: Role of salivary glands and stomach in digestion GNT Block Color Index: • • • • • • Main text Female slides Male slides Important Doctor’s notes Extra notes Editing file: Objectives: Understand the principle and importance of digestion of dietary foodstuffs. Understand the role of salivary...

L2: Role of salivary glands and stomach in digestion GNT Block Color Index: • • • • • • Main text Female slides Male slides Important Doctor’s notes Extra notes Editing file: Objectives: Understand the principle and importance of digestion of dietary foodstuffs. Understand the role of salivary glands in digestion. Understand the role of stomach in digestion Lecture presented by : Dr. Rana Hasanato Dr. Ahmed Mujamammi Background Female Slides Digestion: ● Mechanical effects: ○ e.g., mastication text effects: ● Enzymatic ○ Digestive enzymes (hydrolases) 01 Dietary foodstuffs : Most of dietary foodstuffs are ingested in the form that cannot be readily absorbed from the digestive tract. 02 Processes of the digestive system: 1. Motility text 2. Secretion 3. Absorption 4. Elimination 03 Digestion : The breakdown of the naturally occurring foodstuffs into smaller, easily absorbable forms. End product of digestion Carbohydrates Monosaccharides Triacylglycerols (TAG) Fatty acids & monoacylglycerols Proteins Amino acids 04 Role of salivary glands In digestion The salivary glands secrete saliva that act as lubricant and contains: ● lingual lipase ● salivary ɑ-amylase Salivary ɑ-amylase Secreted by Optimum PH Substrate Hydrolases Produces Important Parotid glands 6.6-6.8 Starch and glycogen ɑ(1,4) glycosidic bonds Short oligosaccharides Simple sugars Types of sugars: Disaccharides Role of salivary glands In digestion Female Slides Digestion Pre-stomach – Salivary amylase : a 1-4 endoglycosidase Female Dr: Salivary Amylase can not work on Disaccharides or a(1,6) bond (Important question in Exam) Effect of ɑ-Amylase on Glycogen Hydrolysis of: ● α(1,4) glycosidic bonds Female Slides Products ● Mixture of short oligosaccharides (both branched & unbranched). ● Disaccharides: Maltose and isomaltose. Role of salivary glands In digestion Salivary ɑ - amylase : Its digestive action on the polysaccharides is of little significance because of the short time during which the enzyme can act on the food in the mouth Salivary amylase is inactivated by the acidity of stomach (The enzyme is inactivated at pH 4.0 or less) Salivary α-amylase does not hydrolyze: α(1,6) glycosidic bonds (The branch points of starch and glycogen) Salivary α-amylase cannot act on: β(1,4) glycosidic bonds of cellulose Salivary α-amylase does not hydrolyze disaccharides *cellulose cannot be digested due to the presence of glycosidic bond B (1,4) Digestion of Carbohydrates in the Mouth Role of Stomach in Digestion 1 No further digestion of carbohydrates. 2 Protein digestion begins by pepsin and rennin. 3 Lipid digestion begins by lingual and gastric lipases. “Lingual lipase starts its action in the stomach” Lingual Lipase ◆ Secreted by the dorsal surface of the tongue (Ebner’s glands) ◆ Acts in the stomach for the digestion of TAG ◆ Produces fatty acids and monoacylglycerols ◆ Its role is of little significance in adult humans Lingual and Gastric Lipases (Acid-Stable Lipases) Substrate End product Role ● TAG molecules, containing medium -and short- chain fatty acids; such as found in milk fat. ● One molecule of 2-Monoacylglycerols and 2 fatty acids. ● Both Lipases role in lipid digestion is of little significance in adult human (the lipid in the stomach is not yet emulsified; Emulsification occurs in duodenum). (Acid-Stable Lipases) Target substrate for acid-stable lipases is TAG containing: as short- or medium-chain fatty acids. Males Dr: “This came in saq multiple times and a lot of students got it incorrect because they wrote 2 molecules of Monoacylglycerols.” Correct answer: One molecule of 2-Monoacylglycerol (No.2 means which carbon) and 2 fatty acids. Lingual and Gastric Lipases Cont. They are important in: Patients with pancreatic insufficiency Neonates and infants -Because there’s absence of pancreatic lipase. -For the digestion of TAG of milk. Digestion of Lipids in Stomach Adults Neonates and infants -No significant effects because of lack of emulsification that occurs in duodenum -Digestion of milk TAG and production of short- and medium-chain fatty acids Digestion of Dietary Proteins in Stomach HCL: Denatures proteins & Activates pepsin Pepsin: Cleaves proteins into polypeptides Rennin: Formation of milk clot Digestion of Dietary Proteins in Stomach Cont. Rennin (not renin which is in kidney) Pepsin Secreted by Chief cells of stomach in neonates and infants Chief cells of stomach as inactive proenzyme, pepsinogen “”activated in stomach into pepsin”” Substrate Casein of milk (in the presence of calcium) Denatured dietary proteins (by HCl) End product Paracasein with the formation of milk clot Smaller polypeptides Additional Effect: It prevents rapid passage of milk from stomach, allowing more time for action of pepsin on milk proteins Acid-stable, endopeptidase *. Activated by HCl and autocatalytically by pepsin. Doctor’s Notes Endopeptidases and Exopeptidases Female Dr: Very helpful and Important Summary Polypeptide Female Dr: Pepsin is Endopeptidase which means it works in the middle not in the Periphery Take Home Messages Digestion involves both mechanical and enzymatic processes Digestion makes dietary foodstuffs readily absorbable by the digestive tract Salivary α-amylase is of limited, but initial effect on digestion of starch and glycogen in the mouth Salivary α-amylase converts starch and glycogen mainly into short oligosaccharides Limited digestion of TAG begins in the stomach by both lingual and gastric lipases producing 2-monoacylglycerols and fatty acids Digestion of proteins begins in the stomach by pepsin producing smaller polypeptides In neonates and infants, digestion of milk occurs in stomach by: - Acid-stable lipases for digestion of milk fat - Rennin and pepsin for digestion of milk proteins Quiz MCQs Q1: Which of the following is responsible for Pepsinogen activation? Q2: Which organ is responsible for the mechanical breakdown of food by churning and mixing? A- HCl B- Rennin C- lingual lipase D- Gastric lipase A- Small intestine B- Liver C- Stomach D- Pancreas Q3: Proteins & lipid digestion starts in? Q4: Rennin acts on casein in the presence of? A- Mouth B- Stomach C- Intestines D- Esophagus A- Calcium B- Phosphate C- Sodium D- Potassium Q5: Lingual lipase is secreted by? Q6: What is Salivary α-Amylase Optimum pH? A- Chief cells of stomach B- Ebner’s glands C- Pituitary gland D- Parotid gland A- 2.5 - 4 B- 6.6 - 6.8 C- 6.8 - 7.0 D- 8 - 12 Answers: 1-A, 2-C ,3-B ,4-A ,5-B ,6-B SAQ Q: What is the role of HCL, Pepsin and Rennin in Digestion? A: HCL: Denatures proteins & Activates pepsin Pepsin: Cleaves proteins into polypeptides Rennin: Formation of milk clot Q: What is the END Product of Lingual and Gastric Lipases (Acid-Stable Lipases)? A: - One molecule of 2-Monoacylglycerols and 2 fatty acids. Members board Team Leaders Raghad Alhamid Remas Aljeaidi Mohammed Alqutub Team Members Leen Alduaij Zeyad Alotaibi Sultan Almishrafi Wafa Alakeel Mohammed Alarfaj Juwan Al Musma Madawi Alhussain Nazmi A Alqutub Wasan Alanazi Leen K Althunayan Faisal Alshowier Aishah boureggah Dana A Alkheliwi Osama Almashjari Mansour Alotaibi Aldanah Abdullah Nazmi M Alqutub Salma Alsaadoun Layan Al-Ruwaili Fahad Mobeirek Abdulrahman Alosleb Areej Alquraini Sarah Alajaji Waad alqahtani Special Thanks to Aleen Alkulyah for the Design! [email protected]