Pathophysiology – Chapter 36: Gastrointestinal Disorders

Review of the Gastro-Intestinal (GI) System Anatomy

• Major components (in oral → anal order)
  • Salivary glands: parotid, submandibular, sublingual
  • Mouth → pharynx → esophagus (pierces diaphragm)
  • Stomach (adjacent to spleen)
  • Accessory organs whose ducts empty into duodenum
  • Liver + gall-bladder (common bile duct)
  • Pancreas (pancreatic duct)
  • Small intestine (duodenum → jejunum → ileum)
  • Large intestine: cecum (+ appendix) → ascending, transverse, descending, sigmoid colon → rectum → anus
• Functional highlights
  • Lower esophageal sphincter (LES) prevents reflux
  • Peristalsis propels food; segmentation mixes chyme

General Manifestations of GI Disorders

• \textbf{Dysphagia} – difficulty swallowing; subdivided into
  • Problems of delivery (neuromuscular, structural)
  • Esophageal obstruction
  • LES dysfunction
• Esophageal pain & abdominal pain: may be visceral (diffuse, cramping) or somatic (sharp, localized)
• Vomiting (emesis): medullary reflex that can lead to fluid / electrolyte imbalance
• Intestinal gas: swallowed air, bacterial fermentation, malabsorptive states
• Altered bowel patterns
  • \textbf{Constipation} – infrequent/ hard stools
  • \textbf{Diarrhea} – ↑frequency & fluidity; osmotic, secretory, exudative, or motility-related

Disorders of the Mouth & Esophagus

Oral Infections – Stomatitis

• Ulcerative inflammation of oral mucosa (lips, buccal mucosa, palate)
• Etiologies: bacteria, viruses, mechanical trauma, alcohol, tobacco, chemotherapeutic agents

Gastroesophageal Reflux Disease (GERD)

• Retrograde flow of gastric contents through incompetent LES
• May be symptomatic (heartburn, regurgitation) or silent
• Complication: \textbf{Barrett esophagus} – metaplastic columnar epithelium replaces distal esophageal squamous lining
  • Carries high risk for adenocarcinoma ⇒ routine endoscopic surveillance + acid-suppressive therapy

Structural / Motor Esophageal Disorders

• Illustrated mechanisms (slide 6)
  • Scar tissue contraction → stricture
  • Tumor compression
  • Congenital atresia or tracheoesophageal fistula
  • Diverticulum with food trapping
  • Achalasia – loss of distal esophageal peristalsis; LES fails to relax

Hiatal Hernia

• Diaphragmatic defect allows stomach herniation into thorax
  • \textit{Sliding} type – gastroesophageal junction moves above diaphragm
  • \textit{Para-esophageal} (rolling) – fundus herniates beside esophagus; junction stays put → strangulation risk

Mallory–Weiss Syndrome

• Longitudinal mucosal/submucosal tear at gastro-esophageal junction
• Trigger: forceful or prolonged vomiting while UES fails to relax → upper GI bleed

Esophageal Varices

• Dilated submucosal veins secondary to portal hypertension (cirrhosis ≈ alcoholism/viral hepatitis)
• Rupture → massive hematemesis, high mortality

Alterations in GI Wall Integrity

Gastritis

• Inflammation of gastric mucosa
  • \textit{Acute} – toxins, NSAIDs, alcohol, infections
  • \textit{Chronic superficial} – universally linked to \textit{Helicobacter pylori} colonization ⇒ persistent inflammation, ↑cancer risk

Gastroenteritis

• Inflammation of stomach + small intestine; direct infection most common (viral > bacterial > parasitic). May be acute or chronic

Peptic Ulcer Disease (PUD)

• Break in mucosa of stomach, duodenum, or lower esophagus due to acid + pepsin
• Major precipitants: H. pylori and NSAID use
• Classic symptom: epigastric burning relieved by food (esp. dairy) or antacids

Inflammatory Bowel Disease (IBD)

Ulcerative Colitis (UC)

• Continuous superficial inflammation of rectum → colon mucosa
• Presents with bloody diarrhea + abdominal pain
• Extent categories
  • Limited to rectum / rectosigmoid
  • Subtotal (beyond sigmoid)
  • Total colitis (pancolitis)

Crohn Disease

• Granulomatous transmural inflammation; "skip lesions"
• Affects any GI segment; commonest = proximal colon ± terminal ileum
• Complications: fistulae, strictures, abscesses, malabsorption

Enterocolitis

• \textbf{Clostridioides difficile} colitis (pseudomembranous)
  • Antibiotic exposure → toxin-mediated mucosal necrosis ± systemic sepsis
• \textbf{Necrotizing Enterocolitis (NEC)}
  • Premature or low-birth-weight neonates (< 34 wks, < 2.25 kg)
  • Diffuse / patchy bowel necrosis; variant “typhlitis” in neutropenic adults
• \textbf{Appendicitis}
  • Most common emergent abdominal surgery
  • Early vague periumbilical pain → migrates to RLQ (McBurney’s point = \frac{2}{3} distance from umbilicus to right ASIS)
  • Nausea, mild fever \approx 100^{\circ}!F, leukocytosis; risk of perforation
• \textbf{Diverticular Disease}
  • Diverticulosis = mucosal out-pouchings; often sigmoid
  • Diverticulitis = inflammation; may bleed or perforate

GI Motility Disorders

• \textbf{Irritable Bowel Syndrome (IBS)} – functional disorder: alternating diarrhea/constipation + crampy pain without structural cause; stress component
• \textbf{Intestinal Obstruction} – mechanical (adhesions, hernia, tumor) or functional (ileus)
• \textbf{Volvulus} – bowel twists around mesentery (cecum, sigmoid) → obstruction + vascular compromise
• \textbf{Intussusception} – telescoping proximal into distal segment; common in infants
• \textbf{Megacolon} – massive dilation; chronic obstipation; congenital (Hirschsprung) or acquired
• \textbf{Hirschsprung Disease} – aganglionic distal colon → functional obstruction in neonate; failure to pass meconium

Malabsorption Syndromes

• General concept: failure to absorb/ digest nutrients → chronic diarrhea, weight loss, steatorrhea
• Causes include enzyme defects, mucosal damage, infections, radiation

Mucosal Disorders

Celiac Disease (Celiac Sprue)

• Immune-mediated intolerance to gliadin (wheat gluten) in genetically predisposed (HLA-DQ2/8)
• Pathology: villous atrophy, crypt hyperplasia, ↓brush border enzymes → malabsorption, diarrhea, failure to thrive, dermatitis herpetiformis

Tropical Sprue

• Similar histology to celiac, but etiology likely bacterial overgrowth in equatorial regions → jejunal/ileal atrophy, B$_{12}$/folate deficiency

Post-surgical Malabsorption

• \textbf{Dumping Syndrome} – rapid gastric emptying into proximal small bowel after partial/total gastrectomy (noted in Roux-en-Y bypass)
• \textbf{Short Bowel Syndrome} – extensive resection → severe diarrhea, nutrient & fluid loss

Neoplasms of the GI Tract

• \textbf{Esophageal Cancer} – 1\%–2\% of all cancers; usually men > 60 y
• \textbf{Gastric Carcinoma} – ≈25 000 U.S. cases/yr, M:F \approx 2:1; risks: H. pylori, smoked foods, atrophic gastritis
• \textbf{Small-Intestinal Tumors} – <5\% of GI neoplasms; may obstruct lumen
• \textbf{Colon Polyps} – any intraluminal protrusion
  • Morphology: sessile vs. pedunculated; benign or pre-/malignant (adenomatous)
• \textbf{Colorectal Cancer}
  • Incidence doubles each decade after 40 until 80 years
  • Early sign: change in bowel habit; late: rectal fullness, dull sacral pain

Psychosocial Aspects of GI Disease

• Chronic disorders provoke lifestyle stress: role dysfunction, impaired family coping, depressive symptoms, trauma response
• Holistic management includes psychological assessment & support

Clinical Correlates from NGN Case Studies

Pediatric Acute Appendicitis (10-y non-verbal)

• Key assessments: RLQ pain, positive McBurney’s sign, fetal-like positioning (knees to chest), anorexia, low-grade fever 99.8^{\circ}!F, mild tachycardia 110\;bpm, guarding/agitation when abdomen touched
• Clinical implications: urgent surgical consult; penicillin allergy relevant for peri-op antibiotics

Adult Peptic Ulcer Disease (Duodenal)

• Effectiveness indicators at 5-wk follow-up (✓):
  • Enrollment in smoking-cessation program (risk modifier)
  • Adherence to sucralfate & clarithromycin (part of quadruple therapy)
  • Successful amoxicillin use (if no allergy)†
  • Biopsy confirmation of H. pylori and subsequent eradication tests (urea breath / stool Ag)
  • Symptom reduction without reliance on antacids
• Non-effective / neutral indicators: strict low-fat/dairy diet (not evidence-based for duodenal PUD), chronic NSAID (ibuprofen) use ↑risk

†Allergy check required because client allergic to peanuts, not penicillin.

Key Numerical / Statistical References

• Esophageal cancer incidence: (1\%–2\%) of all malignancies
• Colorectal cancer incidence doubles every 10 years after 40 y
• Prematurity criteria for NEC: <34 weeks gestation, <2.25\;kg BW
• Temperature descriptors: low-grade fever \approx100.2^{\circ}!F; case data 99.8^{\circ}!F

Practical & Ethical Implications

• Barrett surveillance illustrates preventative ethics: early detection of dysplasia averts cancer
• Antibiotic stewardship vital in preventing C. difficile
• Weight-loss surgeries (Roux-en-Y) demand informed consent regarding dumping syndrome
• Smoking cessation integrated into PUD care highlights biopsychosocial model