Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. Chapter 17 The Digestive System

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 2 Objectives List in sequence each of the component parts or segments of the alimentary canal from the mouth to the anus and identify the accessory organs of digestion List and describe the four layers of the wall of the alimentary canal. Compare the lining layer in the esophagus, stomach, small intestine, and large intestine.

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 3 Objectives List and describe the major disorders of the digestive organs Discuss the basics of protein, fat, and carbohydrate digestion and give the end- products of each process Define and contrast mechanical and chemical digestion Define peristalsis, bolus, chyme, jaundice, ulcer, and diarrhea

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 4 The Digestive System Alimentary canal or GI tract –Extends 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

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6 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)

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 7 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)

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 8 Mouth Floor—formed by tongue and its muscles –Lingual frenulum—fold of mucous membrane that helps anchor the tongue to the floor of the mouth –Papillae—small elevations on mucosa of tongue –Taste buds—found in many papillae

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10 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

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 11 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

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Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 14 Disorders of the Mouth and Teeth Infections, cancer, congenital defects, and other disorders can cause serious complications including malnutrition –Infections and cancer of the mouth may spread to other parts of the body Leukoplakia—precancerous mouth tissue –Snuff dipper’s pouch—from use of chewing tobacco –Squamous cell carcinoma—most common form of mouth cancer

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Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 16 Disorders of the Mouth and Teeth Dental caries –Tooth disease resulting in permanent defect called “cavity” –Infection may spread to other adjacent tissues or to blood –Lost or diseased teeth may be replaced by dentures or implants Gingivitis—gum inflammation or infection –Most cases result from poor oral hygiene –Can be a complication of diabetes, vitamin deficiency, or pregnancy

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Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 18 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, which itches and bleeds easily –Common in immunosuppressed individuals (AIDS) or after antibiotic therapy Periodontitis—inflammation of periodontal membrane –Often a complication of advanced or untreated gingivitis –Leading cause of tooth loss among adults

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Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 20 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

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Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 22 Salivary Glands Three pairs of salivary glands –Secrete about 1 L of saliva/day –Located outside of GI tract –Convey secretions via ducts into tract lumen 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

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Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 24 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

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 25 Pharynx Muscular tube (throat) lined with mucous membrane Functions as part of both respiratory and digestive systems Subdivided into three anatomical segments

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Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 27 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

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 28 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

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Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 30 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)

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 31 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

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 32 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

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Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 35 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

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 36 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

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Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 38 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)

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 39 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

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 40 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

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 41 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

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 42 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

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Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 44 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)

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 45 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

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 46 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

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Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 48 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

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Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 50 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

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 51 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

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Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 53 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

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 54 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

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 55 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

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Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 57 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

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 58 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

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 59 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

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 60 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

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 61 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

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Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 63 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

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Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 65 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

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 66 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

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 67 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

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 68 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

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 69 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

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. 70 Absorption Definition—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