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 Stomach Secretions • 2-3 Liters per day • Mucus – mucous neck cells produce a viscous and alkaline substance that is thick (1.5 mm thick) – Protects lining of stomach from acids • Intrinsic factor – Glycoprotein that is secreted by parietal cells – binds vitamin B12 increasing absorption in ileum. • HCl – Parietal cells produces low pH of stomach (pH 1-3) – HCl kills bacteria (some bacteria have a special coating making them impervious to HCl) – inactivates salivary amylase (stops digestion of carbs) 24-19 – denatures proteins (provides proper pH for pepsin to act). Hydrochloric Acid Production 24-20 Stomach Secretions • Pepsinogen – – – – – – precursor to the active pepsin secreted by chief cells in glands of stomach packaged and released in as zymogen granules converted to pepsin by Hcl most active at pH below 3. catalyzes the cleavage of proteins into smaller peptide chains • Gastrin – produced by endocrine cells of gastric pits. – stimulates additional Hcl and pepsinogen secretion. – secreted in response to stomach filling, caffeine, alcohol consumption 24-21 Phases of Gastric Secretion 24-22 Movements in Stomach 24-23 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 24-24 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 24-25 Duodenum and Pancreas 24-26 Duodenum Anatomy and Histology 24-27 Liver • Lobes – Major: Left and right – Minor: Caudate and quadrate • Ducts – Common hepatic – Cystic • From gallbladder – Common bile • Joins pancreatic duct at hepatopancreatic ampulla 24-28 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 24-29 Blood and Bile Flow 24-30 Duct System 24-31 Gallbladder • Bile is stored and concentrated • Stimulated by cholecystokinin and vagal stimulation • Dumps into small intestine • Production of gallstones possible – Drastic dieting with rapid weight loss 24-32 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 24-33 Bicarbonate Ion Production 24-34 Pancreatic Secretion Control 24-35 Large Intestine • Extends from ileocecal junction to anus • Consists of cecum, colon, rectum, anal canal • Movements sluggish (18-24 hours) 24-36 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 24-37 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 24-38 Histology of Large Intestine 24-39 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 24-40 Reflexes in Colon and Rectum 24-41 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 24-42 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 24-43 Lipids • Include triglycerides, phospholipids, steroids, fat-soluble vitamins • Emulsification breaks down large lipid droplets to small 24-44 Lipoproteins • Types – Chylomicrons • Enter lymph – VLDL – LDL • Transports cholesterol to cells – HDL • Transports cholesterol from cells to liver 24-45 Proteins • Pepsin breaks proteins into smaller polypeptide chains • Proteolytic enzymes produce small peptide chains – Dipeptides, tripeptides, amino acids 24-46 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 24-47 Effects of Aging • Decrease in mucus layer, connective tissue, muscles and secretions • Increased susceptibility to infections and toxic agents – Ulcerations and cancers 24-48