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The Digestive System Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Digestion • Definition—process that transforms food into a form that can be absorbed and used by cells – Mechanical digestion—chewing, swallowing, and peristalsis break food into tiny particles, mix them well with digestive juices, and move them along the digestive tract – Chemical digestion—breaks up large food molecules into compounds having smaller molecules; brought about by digestive enzymes 2 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. The Digestive System • Alimentary canal or GI tract – From mouth to anus—9 m (29 feet) – Involved in digestion, absorption and metabolism of nutrients • System includes main and accessory organs – Main organs: mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anal canal – Accessory organs: teeth and tongue, salivary glands, liver, gallbladder, pancreas, and vermiform appendix 3 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Digestion • Enzymes and chemical digestion – Enzymes—protein molecules that act as catalysts, speeding up chemical reactions – Chemical digestion—specific enzymes speed up breakdown of specific molecules and no others – Hydrolysis—enzymes speed up reactions that add water to break large molecules into smaller molecules 4 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Digestion • Carbohydrate digestion—mainly in small intestine – Pancreatic amylase—changes starches to maltose – Intestinal juice enzymes • Maltase—changes maltose to glucose • Sucrase—changes sucrose to glucose • Lactase—changes lactose to glucose 5 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Digestion • Protein digestion—starts in stomach; completed in small intestine – Gastric juice enzymes, rennin and pepsin, partially digest proteins – Pancreatic enzyme, trypsin, completes digestion of proteins to amino acids – Intestinal enzymes, peptidases, complete digestion of partially digested proteins to amino acids 6 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Digestion • Fat digestion – Bile contains no enzymes but emulsifies fats (breaks fat droplets into very small droplets) – Pancreatic lipase changes emulsified fats to fatty acids and glycerol in small intestine 7 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Absorption • Digested food moves from intestine into blood or lymph • Absorption site—foods and most water are absorbed from small intestine; some water also absorbed from large intestine 8 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 9 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Mouth • Also known as oral cavity—hollow chamber with a roof, floor, and walls • Roof—formed by hard palate (parts of maxillary and palatine bones) and soft palate (an arch-shaped muscle separating mouth from pharynx) 10 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Mouth • Uvula—a downward projection of the soft palate – Uvula and soft palate prevent food and liquid from entering nasal cavities – Assists in speech and swallowing (deglutition) 11 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Mouth • Floor—formed by tongue • Lingual frenulum — helps anchor the tongue to the floor of the mouth – Taste buds—found in many papillae 12 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 13 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Teeth • Types of teeth—incisors, cuspids, bicuspids, and tricuspids – Deciduous (also known as baby or primary) teeth—full set equals 20 teeth • First tooth erupts at about 6 months • Complete set in place at about 2 years of age 14 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Teeth • Permanent teeth—full set equals 32 in most; 28 teeth is a normal variation in others – First permanent tooth erupts at about 6 years of age – Set complete between ages 17 and 24 years • Structures of a typical tooth—crown, neck, and root Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 15 16 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 17 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 18 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 19 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Disorders of the Mouth and Teeth • Infections, cancer, congenital defects, and other disorders can cause serious complications including malnutrition • Leukoplakia—precancerous mouth tissue – Snuff dipper’s pouch—from use of chewing tobacco – Squamous cell carcinoma—most common form of mouth cancer 20 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 21 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Disorders of the Mouth and Teeth • Dental caries “cavity” – Food + bacteria = acid • Gingivitis—gum inflammation or infection – Most cases result from poor oral hygiene – Can be a complication of diabetes, vitamin deficiency, or pregnancy 22 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Disorders of the Mouth and Teeth • Thrush, or oral candidiasis—caused by yeastlike fungal organism – Patches of “cheesy”-looking exudate form over an inflamed tongue and oral mucosa • Periodontitis—inflammation of periodontal membrane – Often a complication of advanced or untreated gingivitis – Leading cause of tooth loss among adults 23 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 24 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Disorders of the Mouth and Teeth • Cleft lip and cleft palate are most common types – May occur alone or together – Caused by failure of mouth structures to fuse during embryonic development 25 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 26 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Salivary Glands • Three pairs of salivary glands – Secrete about 1 L of saliva/day – Located outside of GI tract – Convey secretions via ducts – Parotid glands—largest of salivary glands – Located in front of ear at angle of jaw – Ducts open into mouth opposite second molars – Inflamed in mumps 27 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 28 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Salivary Glands • Submandibular glands—ducts open on either side of lingual frenulum • Sublingual glands—ducts open into floor of mouth • Saliva contains salivary amylase— begins digestion of carbohydrates 29 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Pharynx • Muscular tube (throat) lined with mucous membrane • Functions as part of both respiratory and digestive systems • Subdivided into three anatomical segments 30 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 31 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Wall of the Digestive Tract • Lumen—hollow space within the “tube” of the digestive tract • Tissue layers of the wall of the digestive tube from inside to outside – Mucosa—mucous epithelium – Muscularis—two layers of smooth muscle that move food through the tube by rhythmic muscular waves known as peristalsis 32 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Wall of the Digestive Tract • Tissue layers (cont’d) – Serosa—serous membrane that covers the outside of abdominal organs • Composed of visceral peritoneum in abdominal cavity • It attaches the digestive tract to the wall of the abdominopelvic cavity by forming folds called mesenteries 33 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 34 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Esophagus • Muscular, mucus-lined tube about 25 cm (10 inches) long • Connects pharynx with stomach • Muscular walls help push food toward stomach • Sphincters at each end of esophagus help keep ingested material moving in one direction down the tube – Upper esophageal sphincter (UES) – Lower esophageal sphincter (LES) 35 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Esophagus • GERD—gastroesophageal reflux disease – Backflow of acidic stomach contents into esophagus causes symptoms of heartburn and indigestion – Mild symptoms treated by nonsurgical measures include dietary changes, weight loss, acid-blocking or buffering medications, and drugs that strengthen LES 36 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Esophagus • GERD – Severe and frequent episodes of GERD can trigger asthma attacks, cause severe chest pain, bleeding, or narrowing and chronic irritation of esophagus (Figure 17-12) – Untreated GERD may result in a precancerous condition called Barrett esophagus – Common symptom of hiatal hernia 37 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 38 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 39 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Stomach • Pouch for food that lies in upper part of abdominal cavity just under diaphragm – The size of a large sausage when empty – Expands considerably after a large meal • Contraction of muscular walls of stomach mixes food with gastric juice and breaks it down into chyme 40 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Stomach • Mucous membrane lines the stomach – Membrane lies in folds (rugae) when stomach is empty – Many microscopic glands secrete gastric juice and hydrochloric acid into stomach • Divisions of stomach—fundus, body, and pylorus • Pyloric sphincter muscle closes opening of pylorus (lower part of stomach) to retain food to facilitate partial digestion 41 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 42 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 43 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 44 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 45 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Disorders of the Stomach • Gastroenterology—study of stomach and intestines and their diseases – Stomach is site of numerous diseases and conditions – Gastric diseases often exhibit the following signs or symptoms: gastritis (inflammation), anorexia (appetite loss), nausea (upset stomach), and emesis (vomiting) 46 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Disorders of the Stomach • Pylorospasm—abnormal spasms of the pyloric sphincter – Common in infants – Pyloric stenosis is similar abnormality—obstructive narrowing of the pyloric opening • Ulcers—open wounds caused by acid in gastric juice – Often occurs in duodenum or stomach – Associated with infection by the bacterium Helicobacter pylori and use of NSAIDs – Current treatment involves triple therapy 47 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Disorders of the Stomach • Stomach cancer – Associated with consumption of alcohol or preserved food and use of chewing tobacco – No practical way to screen for early stages 48 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Small Intestine • About 7 m (20 feet) long but only 2 cm or so in diameter • Divisions – Duodenum – Jejunum – Ileum • Wall—contains smooth muscle fibers that contract to produce peristalsis 49 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Small Intestine • Lining—mucous membrane; many microscopic glands (intestinal glands) secrete intestinal juice; villi (microscopic finger-shaped projections from surface of mucosa into intestinal cavity) contain blood and lymph capillaries 50 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 51 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Disorders of the Small Intestine • Enteritis—intestinal inflammation • Gastroenteritis—inflammation of stomach and intestines • Malabsorption syndrome—group of symptoms resulting from failure to absorb nutrients properly (anorexia, abdominal bloating, cramps, anemia, and fatigue) 52 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Liver and Gallbladder • Liver – Size and location • Liver is largest gland • Fills upper right section of abdominal cavity and extends over into left side – Classified as exocrine gland • Secretes bile • Has a variety of metabolic functions 53 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Liver and Gallbladder • Liver – Ducts • Hepatic—drains bile from liver • Cystic—duct by which bile enters and leaves gallbladder • Common bile—formed by union of hepatic and cystic ducts and drains bile from hepatic or cystic ducts into duodenum • Gallbladder – Location—undersurface of the liver – Function—concentrates and stores bile produced in the liver 54 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 55 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Disorders of the Liver and Gallbladder • Gallstones—calculi (stones) made of crystallized bile pigments and calcium salts – Cholelithiasis—condition of having gallstones – Cholecystitis—inflammation of the gallbladder; may accompany cholelithiasis – Stones can obstruct bile canals, causing jaundice 56 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 57 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Disorders of the Liver and Gallbladder • Hepatitis—liver inflammation – Characterized by liver enlargement, jaundice, anorexia, discomfort, gray-white feces, and dark urine – Caused by a variety of factors—toxins, bacteria, viruses, and parasites 58 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Disorders of the Liver and Gallbladder • Cirrhosis—degeneration of liver tissue involving replacement of normal (but damaged) tissue with fibrous and fatty tissue • Portal hypertension—high blood pressure in the hepatic portal veins caused by obstruction of blood flow in a diseased liver; may cause varicosities of surrounding systemic veins 59 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 60 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Pancreas • Location—behind stomach • Functions – Pancreatic cells secrete pancreatic juice into pancreatic ducts; main duct empties into duodenum – Pancreatic islets (of Langerhans)—cells not connected with pancreatic ducts; secrete hormones glucagons and insulin into the blood 61 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Pancreas • Pancreatic disorders – Pancreatitis—inflammation of pancreas • Acute pancreatitis results from blocked ducts that force pancreatic juice to backflow • Pancreatic enzymes digest the gland – Cystic fibrosis—thick secretions block flow of pancreatic juice – Pancreatic cancer is very serious—fatal in the majority of cases 62 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Large Intestine • Size and location—1.5 m long; forms lower, or terminal, portion of digestive tract • Divisions – Cecum – Colon—ascending, transverse, descending, and sigmoid – Rectum – Anal canal • Opening to exterior—anus 63 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 64 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Disorders of the Large Intestine • Disorders of the large intestine often relate to abnormal motility (rate of movement of contents) – Diarrhea—results from abnormally increased intestinal motility; may result in dehydration or convulsions – Constipation—results from decreased intestinal motility – Diverticulitis (inflammation of abnormal outpouchings called diverticula)—may cause constipation 65 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Disorders of the Large Intestine – Colitis—general name for any inflammatory condition of the large intestine – Colorectal cancer—a common malignancy of the colon and rectum associated with colonic polyps; advanced age; low-fiber, high-fat diets; and genetic predisposition 66 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Appendix and Appendicitis • Vermiform appendix is blind tube attached directly to cecum; no important digestive function in humans • Appendicitis—inflammation or infection of appendix – If appendix ruptures, infectious material may spread to other organs – Most common acute abdominal condition requiring surgery – Affects 7% to 12% of population younger than 30 years 67 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Peritoneum • Description—large sheet of serous membrane – Parietal layer of peritoneum lines abdominal cavity – Visceral layer of peritoneum covers abdominal organs – Peritoneal space lies between parietal and visceral layers 68 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Peritoneum • Extensions of peritoneum—largest are the mesentery and greater omentum – Mesentery—extension of parietal peritoneum, which attaches most of small intestine to posterior abdominal wall – Greater omentum, or “lace apron”—hangs down from lower edge of stomach and transverse colon over intestines 69 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 70 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Peritoneum • Peritonitis—inflammation of peritoneum resulting from infection or other irritant; often a complication of ruptured appendix • Ascites—abnormal accumulation of fluid in peritoneal space, often causes bloating of abdomen 71 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 72 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc.