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Bio217 Fall 2012 Unit IX

Gastrointestinal Tract (GI Tract, Alimentary canal) Bio217: Pathophysiology Class Notes Professor Linda Falkow Mouth  Unit IX: Digestive System Disorders  Chapter 33: Structure and Function of the Digestive System 

Chapter 34: Alterations of Digestive Function Anus

Gastrointestinal Tract Gastrointestinal Tract • Histology • Ingestion of food – Mucosa • Propulsion of food and wastes from mouth – to anus (peristalsis) – Muscularis • Secretion of mucus, water, and enzymes – Serosa • Mechanical digestion of food particles or • Chemical digestion of food particles • Absorption of digested food • Elimination of waste products by defecation

Stomach Gastric Secretion

• Stomach secretes large volumes of gastric juices

– Mucus (protective barrier) – Acid (HCl - activate enz., bactericide) – Enzymes (pepsin – proteolytic) – Hormones (gastrin – stim. gastric act.)

– Intrinsic factor (absorption of Vit. B12)

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Gastric Pits and Small Intestine

• 5 to 6 meters long • Three segments – – – • • – Peritoneal cavity

Small Intestine Small Intestine

• Muscle layers – Outer—longitudinal – Inner—circular • Myenteric plexus • Mucosal folds (plica) • Villi • Microvilli – = Brush border • • Lacteal

Intestinal Digestion and Absorption Intestinal Digestion and Absorption

• Hydrochloric acid • Pepsin • Pancreatic enzymes • Intestinal enzymes • Bile salts

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Large Intestine Large Intestine • Ileocecal valve • • O’Beirne sphincter (sigmoid into rectum) • • • Colon • – Ascending – Transverse • Taenia coli – Descending • Haustra – Sigmoid • Rectum • Anus

Gastrointestinal Absorption Accessory Organs of Digestion

Accessory Organs of Digestion Liver

• Liver – Lobes • Separated and attached to the anterior by the falciform ligament • Right lobe –Caudate and quadrate lobes • Left lobe – Glisson capsule

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Hepatic Portal Circulation Liver Lobules

Vascular and Hematologic Vascular and Hematologic Liver Functions Liver Functions • Blood storage • Metabolizes proteins • Bacterial and foreign particle removal • Metabolizes carbohydrates • Synthesizes clotting factors • Metabolic detoxification • Produces bile to absorb fat-soluble vitamins • Storage of minerals and vitamins • Metabolizes fats

Gallbladder Exocrine Pancreas

• Gallbladder is a saclike that lies on • Exocrine pancreas is composed of acini and inferior surface of the liver networks of ducts that secrete enzymes and alkaline fluids to assist in digestion • Function of gallbladder is to store & • Pancreatic duct (Wirsung duct) concentrate bile between meals • Ampulla of Vater • Gallbladder holds about 90 mL of bile

• Bile = emulsifies fats

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Exocrine Pancreas Exocrine Pancreas

• Secretions – Potassium, sodium, bicarbonate, magnesium, calcium, and chloride • Enzymes – Trypsinogen, chymotrypsinogen, and procarboxypeptidase – Trypsin inhibitor – Pancreatic alpha-amylase – Pancreatic lipase

Concept Check:

1. The muscularis layer of the digestive tract is: 4. What is not an example of mechanical digestion? A. skeletal muscle throughout A. Chewing B. the layer that contains blood vessels for the wall B. Churning and mixing of food in stomach C. composed of keratinized epithelium C. Peristalsis and mastication D. composed of circular and longitudinal fibers D. Conversion of proteins a.a.

2. Name the correct sequence of the GI tract layers from the 5. Which part of the S.I. is most distal from ? lumen going out: A. Jejunum B. pyloric sphincter 3. Which layer of the S.I. includes microvilli? C. Duodenum A. submucosa C. muscularis D. Cardiac sphincter B. mucosa D. serosa

Alterations of Digestive Function Clinical Manifestations of Gastrointestinal Dysfunction

• Anorexia Chapter 34 – Lack of a desire to eat despite physiologic stimuli that would normally produce hunger • (emesis) – Forceful emptying of the stomach and intestinal contents through the mouth • – Subjective experience associated with a number of conditions – Common symptoms of vomiting are hypersalivation and tachycardia

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Clinical Manifestations of Clinical Manifestations of Gastrointestinal Dysfunction Gastrointestinal Dysfunction • • – Constipation is defined as infrequent or difficult – Increased frequency of bowel movements defecation – Increased volume, fluidity, weight of the feces – Pathophysiology – Major mechanisms of diarrhea • Neurogenic disorders, low-residue diet, • Osmotic diarrhea (lactase deficiency) sedentary lifestyle, excessive use of antacids • Secretory diarrhea (excess mucosal secretions due (Ca carbonate), use of opiates (codeine) to bacteria) –Following antibiotic therapy • Motility diarrhea (increased motility due to intestinal )

Disorders of Motility Achalasia

• – Dysphagia is difficulty swallowing – Types • Mechanical obstructions (tumors, diverticular Increase in LES muscle tone; herniations) loss of peristalsis in esophagus • Functional obstructions (neural or muscular) – Achalasia • Denervation of in the esophagus and lower esophageal sphincter relaxation

Disorders of Motility Disorders of Motility • Hiatal • Gastroesophageal reflux disease(GERD) – Defect in esophageal hiatus permits part of stomach to – enter thoracic cavity – Caused by: – Reflux of chyme (high acid) from stomach to • esophagus • – If of esophagus • – Less LES pressure means more reflux • Constrictive clothes • Bending, straining, coughing – Occurs with: • Reflux, peptic ulcer, g.b. disorders (inflammation & stones), ,

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Hiatal Hernia

- inflammatory disorder of the A. Sliding hiatial hernia- Stomach moves into • Acute gastritis – erosion of superficial thoracic cavity epithelium (due to drugs or chemicals)

• Chronic gastritis – thinning degeneration of B. Paraesophageal – stomach wall (elderly) Greater curvature herniates through 2nd opening

Peptic Ulcer Disease • A break or ulceration in the protective • Duodenal ulcers mucosal lining of lower esophagus, stomach, or duodenum – Most common of the peptic ulcers – Developmental factors • Acute and chronic ulcers • *Helicobacter pylori infection • Superficial – Toxins and enzymes that promote inflammation – Erosions and ulceration • Deep • Hypersecretion of stomach acid and pepsin • *Use of NSAIDs (aspirin, ibuprofen, naproxen) – True ulcers • High gastrin levels • Acid production by cigarette • Stress and ulcer disease – inconclusive major causes of duodenal ulcers Lesions caused by PUD

Duodenal Ulcer Gastric Ulcer

• Gastric ulcers tend to develop in antral A. Deep ulcer – into muscle region of stomach, adjacent to acid- layer secreting mucosa of body

B. Sequence of ulcer • Pathophysiology formation (normal – Primary defect is an increased mucosal mucosa  duodenal ulcer) permeability to hydrogen ions

– Gastric secretions normal or less than normal C. Bilateral (kissing) ulcers due to NSAIDs

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Inflammatory Bowel Diseases (IBD) Ulcerative • Chronic, relapsing inflammatory bowel disorders of unknown origin • Chronic inflammatory disease that causes (due to genetics, immune system dysfunction, microbes) ulceration of the colonic mucosa – and rectum •

– Affects sigmoid colon and rectum (most often) • Suggested causes • Crohn disease – Infectious, immunologic (anticolon antibodies), – Affects small bowel – regional dietary, genetic (supported by family studies and – Affects colon - Crohn’s disease of colon (or granulomatous colitis) identical twin studies)

Ulcerative Colitis Crohn Disease

• Symptoms • Granulomatous colitis, ileocolitis, or regional – Diarrhea (10 to 20/day), bloody stools, cramping enteritis • Treatment – Broad-spectrum antibiotics and steroids • Idiopathic inflammatory disorder; affects any part – Immunosuppressive agents of digestive tract, from mouth to anus – Surgery • An increased colon cancer risk demonstrated • Difficult to differentiate from ulcerative colitis – Similar risk factors and theories of causation as ulcerative colitis

Diverticular Disease of the Colon • Diverticula • Inflammation of the vermiform appendix – Herniations of mucosa through muscle – (affects 7-12% of pop.) layers of colon wall, especially sigmoid colon • Possible causes – Obstruction, ischemia, increased intraluminal • Diverticulosis pressure  decr. blood flowhypoxia, infection, – Asymptomatic diverticular disease ulceration, etc.

• Epigastric and RLQ • – Inflammatory stage of diverticulosis • Most serious is

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Ascites Ascites

Liver Disorders

• (icterus) Hemolytic jaundice – Greenish, yellow pigmentation of skin due to increased • Excessive hemolysis of red blood cells or plasma bilirubin levels (hyperbilirubinemia) absorption of a hematoma • Extrahepatic Obstructive jaundice • Increased amount of unconjugated bilirubiin – Due to or tumor blockage of common (not water soluble) – Bilirubin conjugated by hepatocytes (liver) cannot enter duodenum  appears in urine (water soluble) • Intrahepatic – Hepatocyte dysfunction  unconjugated bilirubin (fat soluble)

Jaundice

• Irreversible inflammatory chronic disease that disrupts liver function and structure • Decreased hepatic function caused by nodular and fibrotic tissue synthesis (fibrosis)

• Disorganized hepatic tissue  cobbled appearance  impeded blood flow  portal HT  increased pressure  esophageal varicies  GI bleeds

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Cirrhosis Cirrhosis

• Alcoholic (aka portal or nutritional) cirrhosis – and oxidation of alcohol damages hepatocytes

• Biliary (bile canaliculi) – Cirrhosis begins in the bile canaliculi and ducts – Autoimmune or obstructive

Disorders of the Gallbladder Disorders of the Gallbladder • • Obstruction or inflammation () is – Cholesterol stones form in bile that is supersaturated most common cause of gallbladder problems with cholesterol • Gallstones • Cholelithiasis—gallstone formation – Theories – Types • Enzyme defect increases cholesterol synthesis • Cholesterol (most common) and pigmented (cirrhosis) • Decreased secretion of bile acids to emulsify fats – Risks • Decreased resorption of bile acids from ileum • Obesity, middle age, female, Native American ancestry, • Gallbladder smooth muscle hypomotility and stasis and gallbladder, pancreas, or ileal disease • Genetic predisposition

• Combination of any or all of the above

Gallstones Disorders of the Pancreas

• Pancreatitis – Inflammation of the pancreas – Associated with several other clinical disorders • Caused by an injury or damage to pancreatic cells and ducts, causing a leakage of pancreatic enzymes into pancreatic tissue

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Disorders of the Pancreas Digestive System Cancers

• Pancreatitis • Esophagus – relatively rare ( incr. in white males) – These enzymes cause autodigestion of pancreatic • Ulcerations due to reflux tissue and leak into bloodstream to cause • Chronic exposure to irritants (alcohol and tobacco) injury to blood vessels and other organs • Inadequate nutrition

– • Stomach – declining incidence in US (1-2% of new cancers) • Related to chronic alcohol abuse and – H. pylori obstruction (gallstones) – Heavy use of salt & nitrates – Low intake fruits and veg. – Alcohol & tobacco use

Stomach Cancer

• Colon and rectum – 3rd most common cause of cancer and cancer death in US – Age – High fat, low fiber diet – Alcohol & tobacco use – Obesity – Family history – potato

Colon Cancer Colon Cancer by Location Development of Colon Cancer from Adenomatous Polyps

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• 4. Peptic ulcers may be located in the: – A. Stomach C. Duodenum E. A,B,C are correct Concept Check – B. Esophagus D. Colon

• 1. Which of the following does not cause constipation? • 5. Gastric ulcers: – A. Opiates C. hyperthroidism – A. May lead to malignancy – B. Sedentary lifestyle D. Depression – B. Occur at a younger age than duodenal ulcers – • 2. Osmotic diarrhea is caused by: C. Always have incr. acid production – A. Lactase deficiency C. Ulcerative colitis – D. Exhibit nocturnal patterns B. Bacterial endotoxins D. All of the above • 6. In pancreatitis: 3. A common manifestation of hiatal hernia: – A. Tissue damage likely results from rel. of pan. Enz. A. Gastroesophageal reflux C. Postprandial substernal pain – B. High colesterol is the cause B. Diarrhea D. A and C are correct – C. Diabetes is uncommon in chronic panreatitis – D. Bacterial infection is the cause

7. The characteristic lesion of Crohn disease is: A. Found in the ileum B. Precancerous C. Granulomatous D. Both A and C are correct

8. Gastroesophageal reflux is: A. Caused by rapid gastric emptying B. Excessive LES functioning C. Associated with abdominal surgery D. Caused by relaxation of LES

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