Human Physiology, Chapter 21: The Digestive System PDF

Human Physiology, An Integrated Approach 8th Edition Chapter 21 The Digestive System Copyright © 2019, 2016, 2013 Pearson Education, Inc. All R...

Human Physiology, An Integrated Approach 8th Edition Chapter 21 The Digestive System Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Chapter Summary 21.1 Anatomy of the Digestive System 21.2 Digestive Function and Processes 21.3 Regulation of GI Function 21.4 Integrated Function: The Cephalic Phase 21.5 Integrated Function: The Gastric Phase 21.6 Integrated Function: The Intestinal Phase 21.7 Immune Functions of the GI Tract Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Learning Outcomes 1. Trace a piece of undigested food from mouth to anus. 2. Describe the four layers of the GI tract wall. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 21.1 Anatomy of the Digestive System Digestive system is a tube Oral cavity Gastrointestinal (GI) tract Accessory organs Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 21.1 Anatomy of the Digestive System The GI Tract Wall Has Four Layers Modifications increase surface area and match functions of various areas – Rugae and plicae – Villi – Gastric glands, crypts, and submucosal glands Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 21.1 Anatomy of the Digestive System The GI Tract Wall Has Four Layers Modifications increase surface area and match functions of various areas – Rugae and plicae – Villi – Gastric glands, crypts, and submucosal glands Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 21.1 Anatomy of the Digestive System The GI Tract Wall Has Four Layers Modifications increase surface area and match functions of various areas – Rugae and plicae – Villi – Gastric glands, crypts, and submucosal glands Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 21.1 Anatomy of the Digestive System The GI Tract Wall Has Four Layers 1. Mucosa – Mucosal epithelium – Lamina propria (connective tissue) – Muscularis mucosae 2. Submucosa – Connective tissue – Contains submucosal plexus of the enteric nervous system 3. Muscularis externa – Consists of two layers of smooth muscle – Contains myenteric plexus of the enteric nervous system 4. Serosa – Continuation of the peritoneal membrane, which forms sheets of mesentery Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Chapter Summary 21.1 Anatomy of the Digestive System 21.2 Digestive Function and Processes 21.3 Regulation of GI Function 21.4 Integrated Function: The Cephalic Phase 21.5 Integrated Function: The Gastric Phase 21.6 Integrated Function: The Intestinal Phase 21.7 Immune Functions of the GI Tract Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Learning Outcomes 3. Describe the primary function of the digestive system. 4. Explain the challenges of autodigestion, mass balance, and defense. 5. Describe and compare secretion, digestion, absorption, and motility. 6. Describe single-unit smooth muscle, slow wave potentials, tonic and phasic contractions. 7. Describe and compare peristalsis, segmentation, and the migrating motor complex. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 21.2 Digestive Function and Processes Digestive function – To move nutrients, water, and electrolytes from external environment into internal environment. Four basic processes – Digestion – Absorption – Secretion – Motility Three Challenges – Avoiding autodigestion – Mass balance – Defense Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 21.2 Digestive Function and Processes Digestive function – To move nutrients, water, and electrolytes from external environment into internal environment. Four basic processes – Digestion – Absorption – Secretion – Motility Three Challenges – Avoiding autodigestion – Mass balance – Defense Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 21.2 Digestive Function and Processes We Secrete More Fluid than We Ingest 9 L/day of fluid pass through lumen of digestive tract – 2 L/day are consumed + 7 L/day from secretions Digestive enzymes – Secreted into the mouth, stomach, and intestine – May be secreted as inactive proenzymes, called zymogens  activated Mucus – Mucins produced by mucous cells, serous cells, and goblet cells Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  21.2 Digestive Function and Processes Motility: GI Smooth Muscles Contracts Spontaneously 2 purposes – Moving food through the tract (peristalsis) – Mechanically mixing food to break it into uniformly small particles (segmentation) Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  21.2 Digestive Function and Processes Motility: GI Smooth Muscles Contracts Spontaneously Different regions exhibit different types of contractions – Tonic contractions – minutes or hours – Phasic contractions - seconds Slow-wave potentials are spontaneous depolarizations Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Chapter Summary 21.1 Anatomy of the Digestive System 21.2 Digestive Function and Processes 21.3 Regulation of GI Function 21.4 Integrated Function: The Cephalic Phase 21.5 Integrated Function: The Gastric Phase 21.6 Integrated Function: The Intestinal Phase 21.7 Immune Functions of the GI Tract Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Learning Outcomes 8. Compare the enteric nervous system to the central nervous system. 9. Contrast long reflexes, short reflexes, and control involving GI peptides. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 21.3 Regulation of GI Function The enteric nervous system can act independently Controls motility, secretion and growth of the digestive system – Intrinsic neurons are neurons in ENS (extrinsic are from CNS to digestive system) Shares features with CNS – Neurotransmitters and neuromodulators – Glial support cells – Diffusion barrier (like blood-brain barrier) – Integrating center Short reflexes integrate in the enteric nervous system Long reflexes integrate in CNS – Called cephalic reflexes Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 21.3 Regulation of GI Function The enteric nervous system can act independently Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Learning Outcomes 10.Name the three families of GI hormones, and give examples of each. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 21.3 Regulation of GI Function GI Peptides Include Hormones, Neuropeptides, and Cytokines GI peptides excite or inhibit GI motility and secretion GI hormones – 3 main GI hormone families 1. Gastrin family – Gastrin – Cholecystokinin (CCK) 2. Secretin family – Secretin – Vasoactive intestinal peptide (VIP) – Glucose-dependent insulinotropic peptide (GIP) – Glucagon-like peptide-1 (GLP-1) 3. Others – Motilin Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 21.3 Regulation of GI Function GI Peptides Include Hormones, Neuropeptides, and Cytokines © 2016 Pearson Education, Inc. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved © 2016 Pearson Education, Inc. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved © 2016 Pearson Education, Inc. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved © 2016 Pearson Education, Inc. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved © 2016 Pearson Education, Inc. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved ation, Inc. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Chapter Summary 21.1 Anatomy of the Digestive System 21.2 Digestive Function and Processes 21.3 Regulation of GI Function 21.4 Integrated Function: The Cephalic Phase 21.5 Integrated Function: The Gastric Phase 21.6 Integrated Function: The Intestinal Phase 21.7 Immune Functions of the GI Tract Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Learning Outcomes 11.Explain feedforward control in digestion. 12.Map the processes and control pathways of the cephalic phase. 13.Explain the functions of saliva and the process by which it is secreted. 14.List the steps of the deglutition (swallowing) reflex. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 21.4 Integrated Function: The Cephalic Phase Feed forward control Smelling, seeing, or thinking about food – Reflex begins in brain – Anticipation of or presence of food in oral cavity activates neurons in medulla – Initiates cephalic phase Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 21.4 Integrated Function: The Cephalic Phase Chemical and mechanical digestion begins in the mouth Salivary secretions – Exocrine – Under autonomic control – Have 4 functions 1. Soften and lubricate food 2. Digestion of starch (chemical) 3. Taste 4. Defense Mechanical digestion begins with chewing – Mastication Swallowing moves food from mouth to stomach – Deglutition – Epiglottis closes off airways Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Chapter Summary 21.1 Anatomy of the Digestive System 21.2 Digestive Function and Processes 21.3 Regulation of GI Function 21.4 Integrated Function: The Cephalic Phase 21.5 Integrated Function: The Gastric Phase 21.6 Integrated Function: The Intestinal Phase 21.7 Immune Functions of the GI Tract Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Learning Outcomes 15.Map the processes and control pathways of the gastric phase. 16.Describe the gastric secretions and their major actions. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 21.5 Integrated Function: The Gastric Phase 3 functions of the stomach 1. Storage ▪Upper stomach 2. Digestion ▪Lower stomach ▪Lipids and proteins ▪Acid, enzymes, paracrine signal molecules, and hormones 3. Defense ▪Against swallowed pathogens Digestive activity in stomach begins with long vagal reflex of cephalic phase then food in stomach initiates short reflexes of gastric phase Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 21.5 Integrated Function: The Gastric Phase Gastric Secretions Protect and Digest Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 21.5 Integrated Function: The Gastric Phase Gastric Secretions Protect and Digest Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 21.5 Integrated Function: The Gastric Phase Gastric Secretions Protect and Digest Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Chapter Summary 21.1 Anatomy of the Digestive System 21.2 Digestive Function and Processes 21.3 Regulation of GI Function 21.4 Integrated Function: The Cephalic Phase 21.5 Integrated Function: The Gastric Phase 21.6 Integrated Function: The Intestinal Phase 21.7 Immune Functions of the GI Tract Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Learning Outcomes 17. Compare and contrast digestion and motility in the large and small intestines. 18.Describe the anatomy and function of the hepatic portal system. 19.Describe the major secretions of the pancreas and liver. 20.Diagram the cellular mechanisms for secretion or absorption of water and ions. 21.Diagram the digestion and absorption of carbohydrates, proteins, and fats. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 21.6 Integrated Function: The Intestinal Phase Intestinal Secretions Promote Digestion Digestive enzymes Bile Bicarbonate secretion Mucus Isotonic NaCl secretion – Cystic fibrosis transmembrane conductance regulator, or CFTR channel Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  21.6 Integrated Function: The Intestinal Phase The pancreas secretes enzymes and bicarbonate Endocrine portion (islets) – Secretes insulin and glucagon Exocrine portion – Enzyme secretion ▪Brush border enteropeptidase converts trypsinogen to trypsin – Bicarbonate secretion ▪Neutralizes gastric acid Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 21.6 Integrated Function: The Intestinal Phase The liver secretes bile Bile stored and concentrated in the gall bladder Bile helps digest lipids Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 21.6 Integrated Function: The Intestinal Phase Most digestion (and absorption) occurs in the small intestine Pancreatic and brush border enzymes complete digestion – Carbohydrates, lipids, proteins Peristalsis and segmentation Maximization of surface area – Villi and crypts – Brush border Absorbed nutrients from intestinal epithelium – Most go to circulatory system for distribution ▪Hepatic portal system – Fats use lymphatic circulation to enter circulatory system Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 21.6 Integrated Function: The Intestinal Phase Most digestion (and absorption) occurs in the small intestine Pancreatic and brush border enzymes complete digestion – Carbohydrates, lipids, proteins Maximization of surface area – Villi and crypts – Brush border Absorbed nutrients from intestinal epithelium – Most go to circulatory system for distribution ▪Hepatic portal system – Fats use lymphatic circulation to enter circulatory system Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 21.6 Integrated Function: The Intestinal Phase Bile salts facilitate fat digestion – Lingual and gastric lipases begin lipid digestion, assisted by pancreatic lipases in the duodenum – Lipids are absorbed into the apical side of mucosal cells by diffusion – Then packaged and exported from the basolateral side by exocytosis – Enter lymphatic lacteals Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 21.6 Integrated Function: The Intestinal Phase Carbohydrates are absorbed as monosaccharides – Salivary and pancreatic amylases break starches into disaccharides – Brush border enzymes break disaccharides into monosaccharides – Monosaccharides absorbed on apical side through co-transport with sodium (2 O active transport) – Monosaccharides diffuse through transporters on basolateral side – Enter capillaries in villi (b) Carbohydrate absorption in the small intestine (a) Carbohydrates break down into monosaccharides. Glucose Polymers Lumen of intestine Starch, glycogen Glucose or galactose Fructose enters Na+ Glucose enters with on GLUT5 and Na+ on SGLT and exits on GLUT2. Disaccharides exits on GLUT2. Amylase Maltose Sucrose Lactose Na+ Maltase Sucrase Lactase ATP K+ Intestinal KEY mucosa 2 glucose 1 glucose + 1 glucose + SG 1 fructose 1 galactose GL Monosaccharides GL Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 21.6 Integrated Function: The Intestinal Phase (a) Proteins are chains of amino acids. (c) Peptide absorption After digestion, proteins are absorbed mostly as free amino acids. Peptide Carboxy- Proteins are digested into small peptides Amino- Amino A few di- and tripeptides are absorbed. Some peptides larger than terminal end acids bonds terminal end tripeptides can be absorbed by transcytosis. & amino acids H2N COOH – Pepsin begins digestion in the stomach – Pancreatic and intestinal proteases (b) Enzymes for protein digestion Proteins digest further into single amino acids and di- and tri-peptides Endopeptidases include Peptides Endopeptidase pepsin in the stomach, and digests internal trypsin and chymotrypsin peptide bonds. in the small intestine. – Amino acids are absorbed through co- Di- and tripeptides Amino acids Small peptides transport with sodium +H2O cotransport with H + cotransport are carried intact on PepT1. with Na+. across the cell by transcytosis. H2N COOH – Di- and tri-peptides are absorbed via H+ H+ endocytosis 2 smaller peptides H2N COOH H2N COOH – Enter capillaries in villi Na+ Na+ Exopeptidases digest terminal peptide Peptidases bonds to release amino acids. Aminopeptidase Carboxypeptidase K+ +H2O +H2O ATP H2N COOH H+ Na+ Na+ Amino acid Amino acid P eptide H2N COOH H2N COOH H2N COOH Blood To the liver Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 21.6 Integrated Function: The Intestinal Phase Nucleic acids are digested into bases and monosaccharides Intestine absorbs vitamins and minerals – Fat-soluble vitamins are absorbed with fats – Water-soluble vitamins are absorbed by mediated transport ▪Vitamin B12 absorbed in the ileum when complexed to intrinsic factor – Iron and calcium absorption is actively regulated The intestine absorbs ions and water – Solute gradient and ion absorption creates osmotic gradient that draws water into body – Na+ absorption through enterocytes and colonocytes helps create gradient Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Learning Outcomes 22.Explain the neural and hormonal control of the intestinal phase of digestion. 23.Explain the role of bacteria in the gut. 24.Describe the GALT. 25.Contrast the protective reflexes of vomiting and diarrhea. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 21.6 Integrated Function: The Intestinal Phase Regulation of Intestinal Phase Food into stomach Stomach: Nervous and hormonal Food moving into the stomach triggers acid secretion, pepsin and lipase secretion, and gastric motility. Acid secretion Pepsin and lipase secretion Gastric motility Small intestine: Chyme moving into the duodenum triggers Chyme Enteric neural and endocrine reflexes. These into small nervous intestine system 1. Initiate enzyme and bicarbonate secretion; Hyper- Fats, 2. Feed back to slow gastric digestion osmotic Carbohydrates proteins Acid and emptying; solution 3. Feed forward to start insulin secretion. ? Endocrine GIP GLP-1 CCK Secretin cell Pancreas: Secretin stimlulates pancreatic bicarbonate production, Pancreatic Pancreatic CCK stimulates pancreatic enzyme secretion, and Insulin enzyme bicarbonate increatin hormones (GIP & GLP-1) stimulate insulin secretion. secretion secretion secretion Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 21.6 Integrated Function: The Intestinal Phase Large Intestine Concentrates Waste Only about 1.5 L (of 9 L) remains Hepatic portal vein Aorta Tenia coli Lymphoid nodule Intestinal glands are the site of fluid secretion. after ileum Inferior vena cava – Most is absorbed in colon Transverse colon – Only about 0.1 L of water lost in Muscularis mucosae Submucosa feces Segmental contractions continue to Ascending colon mix chime Descending Longitudinal layer colon (tenia coli) Food enters the Muscularis Mass movement moves the chyme large intestine through the ileocecal valve. Ileum Haustra Circular muscle externa forward and triggers defecation Cecum Sigmoid colon – Gastrocolic reflex Appendix – Defecation reflex Rectum Rectum The defecation reflex begins with distension of the rectal wall. ▪Internal anal sphincter Internal anal sphincter External anal sphincter Anus Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 21.6 Integrated Function: The Intestinal Phase Large Intestine Concentrates Waste Digestion and absorption in large intestine – Bacteria inhabiting colon break down much of the undigested material ▪Lipophilic products are absorbed ▪Fatty acids are the energy substrate for colonocytes ▪Vitamins Hepatic portal vein Aorta Tenia coli Lymphoid Intestinal glands are nodule the site of fluid secretion. ▪Flatus Inferior vena cava Transverse colon Diarrhea can cause dehydration Muscularis mucosae Submucosa Ascending colon Descending Longitudinal layer Food enters the colon (tenia coli) Muscularis large intestine through Ileum Haustra Circular muscle externa the ileocecal valve. Cecum Sigmoid colon Appendix Rectum Rectum The defecation reflex begins with distension of the rectal wall. Internal anal sphincter Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved External anal sphincter Anus