Transcript Chapter 24
Anatomy and Physiology, Sixth Edition Rod R. Seeley Idaho State University Trent D. Stephens Idaho State University Philip Tate Phoenix College Chapter 24 Lecture Outline* *See PowerPoint Image Slides for all figures and tables pre-inserted into PowerPoint without notes. 24-1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 24 Digestive System 24-2 Digestive System Anatomy • Digestive tract – Alimentary tract or canal – GI tract • Accessory organs – Primarily glands • Regions – – – – – – – Mouth or oral cavity Pharynx Esophagus Stomach Small intestine Large intestine Anus 24-3 Functions • Ingestion: Introduction of food into stomach • Mastication: Chewing • Propulsion – Deglutition: Swallowing – Peristalsis: Moves material through digestive tract 24-4 Functions • • • • • Mixing: Segmental contraction that occurs in small intestine Secretion: Lubricate, liquefy, digest Digestion: Mechanical and chemical Absorption: Movement from tract into circulation or lymph Elimination: Waste products removed from body 24-5 Digestive Tract Histology 24-6 Digestive System Regulation • Nervous regulation – Involves enteric nervous system • Types of neurons: sensory, motor, interneurons – Coordinates peristalsis and regulates local reflexes • Chemical regulation – Production of hormones • Gastrin, secretin – Production of paracrine chemicals • Histamine • Help local reflexes in ENS control digestive environments as pH levels 24-7 Peritoneum and Mesenteries • Peritoneum – Visceral: Covers organs – Parietal: Covers interior surface of body wall – Retroperitoneal: Behind peritoneum as kidneys, pancreas, duodenum • Mesenteries – Routes which vessels and nerves pass from body wall to organs – Greater omentum – Lesser omentum 24-8 Oral Cavity • Mouth or oral cavity – Vestibule: Space between lips or cheeks and alveolar processes – Oral cavity proper • Lips (labia) and cheeks • Palate: Oral cavity roof – Hard and soft • Palatine tonsils • Tongue: Involved in speech, taste, mastication, swallowing 24-9 Teeth • Two sets – Primary, deciduous, milk: Childhood – Permanent or secondary: Adult (32) • Types – Incisors, canine, premolar and molars 24-10 Teeth 24-11 Salivary Glands • Produce saliva – Prevents bacterial infection – Lubrication – Contains salivary amylase • Breaks down starch • Three pairs – Parotid: Largest – Submandibular – Sublingual: Smallest 24-12 Pharynx and Esophagus • Esophagus • Pharynx – Nasopharynx – Oropharynx: Transmits food normally – Laryngopharynx: Transmits food normally – Transports food from pharynx to stomach – Passes through esophageal hiatus (opening) of diaphragm and ends at stomach • Hiatal hernia – Sphincters • Upper • Lower 24-13 Deglutition (Swallowing) • Three phases – Voluntary • Bolus of food moved by tongue from oral cavity to pharynx – Pharyngeal Reflex: Upper esophageal sphincter relaxes, elevated pharynx opens the esophagus, food pushed into esophagus – Esophageal • Reflex: Epiglottis is tipped posteriorly, larynx elevated to prevent food from passing into larynx 24-14 Phases of Deglutition (Swallowing) 24-15 Stomach Anatomy • Openings – Gastroesophageal: To esophagus – Pyloric: To duodenum • Regions – – – – Cardiac Fundus Body Pyloric 24-16 Stomach Histology • Layers – Serosa or visceral peritoneum: Outermost – Muscularis: Three layers • Outer longitudinal • Middle circular • Inner oblique – Submucosa – Mucosa 24-17 Stomach Histology • Rugae: Folds in stomach when empty • Gastric pits: Openings for gastric glands – Contain cells • Surface mucous: Mucus • Mucous neck: Mucus • Parietal: Hydrochloric acid and intrinsic factor • Chief: Pepsinogen • Endocrine: Regulatory hormones 24-18 Hydrochloric Acid Production 24-19 Phases of Gastric Secretion 24-20 Movements in Stomach 24-21 Small Intestine • Site of greatest amount of digestion and absorption • Divisions – Duodenum – Jejunum – Ileum: Peyer’s patches or lymph nodules • Modifications – Circular folds or plicae circulares, villi, lacteal, microvilli • Cells of mucosa – Absorptive, goblet, granular, endocrine 24-22 Small Intestine Secretions • Mucus – Protects against digestive enzymes and stomach acids • Digestive enzymes – Disaccharidases: Break down disaccharides to monosaccharides – Peptidases: Hydrolyze peptide bonds – Nucleases: Break down nucleic acids • Duodenal glands – Stimulated by vagus nerve, secretin, chemical or tactile irritation of duodenal mucosa 24-23 Duodenum and Pancreas 24-24 Duodenum Anatomy and Histology 24-25 Liver • Lobes – Major: Left and right – Minor: Caudate and quadrate • Ducts – Common hepatic – Cystic • From gallbladder – Common bile • Joins pancreatic duct at hepatopancreatic ampulla 24-26 Functions of the Liver • Bile production – Salts emulsify fats, contain pigments as bilirubin • Storage – Glycogen, fat, vitamins, copper and iron • Nutrient interconversion • Detoxification – Hepatocytes remove ammonia and convert to urea • Phagocytosis – Kupffer cells phagocytize worn-out and dying red and white blood cells, some bacteria • Synthesis – Albumins, fibrinogen, globulins, heparin, clotting factors 24-27 Blood and Bile Flow 24-28 Duct System 24-29 Gallbladder • Bile is stored and concentrated • Stimulated by cholecystokinin and vegal stimulation • Dumps into small intestine • Production of gallstones possible – Drastic dieting with rapid weight loss 24-30 Pancreas • Anatomy – Endocrine • Pancreatic islets produce insulin and glucagon – Exocrine • Acini produce digestive enzymes – Regions: Head, body, tail • Secretions – Pancreatic juice (exocrine) • • • • • • Trypsin Chymotrypsin Carboxypeptidase Pancreatic amylase Pancreatic lipases Enzymes that reduce DNA and ribonucleic acid 24-31 Bicarbonate Ion Production 24-32 Pancreatic Secretion Control 24-33 Large Intestine • Extends from ileocecal junction to anus • Consists of cecum, colon, rectum, anal canal • Movements sluggish (18-24 hours) 24-34 Large Intestine • Cecum – Blind sac, vermiform appendix attached • Colon – Ascending, transverse, descending, sigmoid • Rectum – Straight muscular tube • Anal canal – Internal anal sphincter (smooth muscle) – External anal sphincter (skeletal muscle) – Hemorrhoids: Vein enlargement or inflammation 24-35 Secretions of Large Intestine • Mucus provides protection – Parasympathetic stimulation increases rate of goblet cell secretion • Pumps – Exchange of bicarbonate ions for chloride ions – Exchange of sodium ions for hydrogen ions • Bacterial actions produce gases called flatus 24-36 Histology of Large Intestine 24-37 Movement in Large Intestine • Mass movements – Common after meals • Local reflexes in enteric plexus – Gastrocolic: Initiated by stomach – Duodenocolic: Initiated by duodenum • Defecation reflex – Distension of the rectal wall by feces • Defecation – Usually accompanied by voluntary movements to expel feces through abdominal cavity pressure caused by inspiration 24-38 Reflexes in Colon and Rectum 24-39 Digestion, Absorption, Transport • Digestion – Breakdown of food molecules for absorption into circulation • Mechanical: Breaks large food particles to small • Chemical: Breaking of covalent bonds by digestive enzymes • Absorption and transport – Molecules are moved out of digestive tract and into circulation for distribution throughout body 24-40 Carbohydrates • Consist of starches, glycogen, sucrose, lactose, glucose, fructose • Polysaccharides broken down to monosaccharides • Monosaccharides taken up by active transport or facilitated diffusion and carried to liver • Glucose is transported to cells requiring energy – Insulin influences rate of transport 24-41 Lipids • Include triglycerides, phospholipids, steroids, fat-soluble vitamins • Emulsification breaks down large lipid droplets to small 24-42 Lipoproteins • Types – Chylomicrons • Enter lymph – VLDL – LDL • Transports cholesterol to cells – HDL • Transports cholesterol from cells to liver 24-43 Proteins • Pepsin breaks proteins into smaller polypeptide chains • Proteolytic enzymes produce small peptide chains – Dipeptides, tripeptides, amino acids 24-44 Water and Ions • Water – Can move in either direction across wall of small intestine depending on osmotic gradients • Ions – Sodium, potassium, calcium, magnesium, phosphate are actively transported 24-45 Effects of Aging • Decrease in mucus layer, connective tissue, muscles and secretions • Increased susceptibility to infections and toxic agents – Ulcerations and cancers 24-46