Digestive System Lecture 18 PDF

Digestive system Lecture 18 Digestive system Lecture 18 Learning goals Learn the functions of the digestive system Examine the anatomy of the digestive system Understand accessory organs and their functions Learn the basics of chemical reactor theory Understand mechanical vs. chemical di...

Digestive system Lecture 18 Digestive system Lecture 18 Learning goals Learn the functions of the digestive system Examine the anatomy of the digestive system Understand accessory organs and their functions Learn the basics of chemical reactor theory Understand mechanical vs. chemical digestion Understand the digestive process (including absorption) for proteins and carbohydrates Basic functions of the digestive tract Food SECRETION DIGESTION ABSORPTION MOTILITY Lumen of digestive tract Wall Interstitial Blood fluid Basic anatomy of the Gastrointestinal Tract THE DIGESTIVE SYSTEM Esophagus Fundus Diaphragm Oral cavity Salivary glands Antrum Esophagus Pylorus Gallbladder Liver Pancreas Stomach Small Rugae: Surface folding Large increases area intestine intestine Rectum Basic anatomy of the Stomach Epithelium Rugae Mucosa Esophagus Fundus Diaphragm Gastric Gland Antrum (opening) Lamina propia Muscularis mucosae Pylorus Lymph vessel Submucosa Circular Rugae: Surface folding Muscularis muscle increases area Longitudinal muscle Serosa Myenteric plexus pH 1-3 (extremely acidic) Enzyme Pepsin secreted Protein digestion Basic anatomy of the Intestine Villi Mucosa submucosa muscularis Plica Circular Submucosal muscle plexus pH 7-9 (alkaline) Numerous enzymes Longitudinal muscle Myenteric Peyer’s patch All nutrients, and minerals plexus (lymphoid) Serosa Basic anatomy of the Intestine B 110 µm M Enterocyte F L A Goblet cells F L Villus Crypt C E Microvilli dramatically increase surface area mv L Endocrine cells Three sections compose small intestine (SI) Duodenum: proximal SI. First 25-40 cm Brunner’s glands Ducts empty Starch, fat, protein digestion Jejunum: mid SI. Middle 250 cm Primary site of absorption Membrane bound enzymes No clear barrier w/ Ileum Ileum: distal SI. Final 400 cm Rich in Peyer’s Patch (immune) Bile salts, vitamins absorbed Ileocecal valve Immune function of gut: through “M”-cells Antigens M-cells (bad microbes) Gut associated lymphoid tissue (GALT) M-cells sample illium fluid and pass antigens to immune cells Five sections compose large intestine (LI) 2 1. Ascending colon Runs up right side Includes cecum and appendix 1 2. Transverse colon 3 Runs under diaphragm 3. Descending colon Runs down left side Cecum Appendix 4 4. Sigmoid colon Final bend 5. Rectum Primary function of LI is fluid and electrolyte absorption Primary site of microbial community and fermentation Some vitamins (e.g., Vit K) and amino acids from microbes absorbed Pancreas is endocrine and exocrine NaHCO3 secreted by Islet cells (endocrine) duct cells Digestive enzyme production Bicarbonate buffer (NaHCO3) “Acini” Empties into duodenum Acinar cells (exocrine) Liver is the central distribution center Common hepatic duct Gallbladder Common bile duct Hepatic portal vein (from GI tract) Hepatic artery Liver Glucose and fat metabolism Protein and hormone synthesis Urea production Detoxification, storage Absorbed from GI Tract Hepatic artery Nutrients, drugs, foreign substances From tissues Bilirubin, metabolites, drugs, nutrients Secreted into Duodenum To tissues Bile salts, bilirubin, water, ions Metabolites, proteins, vitamins, urea Basic functions of the digestive tract Food SECRETION DIGESTION ABSORPTION MOTILITY Lumen of digestive tract Wall Interstitial Blood fluid Digestive tract functions like chemical reactor Continuous stirred-tank reactor (CSTR) Reaction rate or [reactant] Input Output ∆ in Particle size Proximal Distal Plug-flow reactor (PFR) Reaction rate or [reactant] Proximal Distal Digestion is mechanical and chemical Mechanical disruption: mastication Chemical digestion saliva: amylase, lipase, lysozyme hydrolysis with enzymes and acid https://www.npr.org/2013/04/12/177029249/down-the-gullet-a-guided-tour-of-your-guts Parotid gland Sublingual gland Submandibular gland Chemical digestion of protein: acid H2N Gly Pro Cys Ile Lys Val Ser Glu Met Cys Arg Thr Tyr Phe Ser Val His COOH Chemical digestion of protein: acid+pepsin H2N Ser Disrupts quaternary, tertiary, and secondary Glu structure Arg Leaves bonds vulnerable to further attack Tyr Thr Cys Met Ser Digestive enzymes: Val “Hydrolytic” His COOH Chemical digestion of protein: endoprotease H2N Ser Pepsin Glu Arg Tyr Thr Cys Met Ser Val His COOH Chemical digestion of protein: proteases Thr Trypsin (endo) Cys Met Carboxypeptidases (exo) Ser Another class of proteases Val Aminopeptidases H2N His Membrane bound COOH Ser Glu Arg Tyr  Absorption of di- and tri-peptides 1 Di- and tri-peptides cotransported with H+ Intestinal lumen Na+ AA H+ AA AA Na+ NHE 2 H exchanged for Na with + + NHE (sodium hydrogen 2 1 exchanger) AA AA a) AA 3 Two possibilities: 3 a) Hydrolyzed to AA, follows AA pathway b) ATP b) Exchanged for H+ H+ K+ Na+ Blood AA AA AA Chemical digestion of carbohydrate CH2OH CH2OH CH2OH CH2OH CH2OH H O O O O O H H H H H H OH H OH H OH H OH H OH H OH O O O O OH H OH H OH H OH H OH H OH Amylase CH2OH CH2OH H O O H Disaccharide (maltose) H OH H H OH H α-glucosidase OH O OH H OH H OH CH2OH H O H Monosaccharide (glucose) H OH H Absorbable OH OH H OH  Absorption of monosaccharides Glucose or galactose Na+ Fructose SGLT GLUT5 Na+ K+ GLUT2 Human adaptation for dietary starch level Japanese Biaka Chimp