Gastrointestinal Disorders Overview

Gastrointestinal Disorders

• Salivary glands include parotid, submandibular, and sublingual glands.
• The oral cavity, pharynx, esophagus, stomach, small intestine (duodenum, jejunum, ileum), colon (ascending, transverse, descending, sigmoid), rectum, and anus are part of the gastrointestinal tract.
• The liver, gallbladder, and pancreas play important roles in digestion.

Anatomy of the GI Tract

• The GI tract is divided into upper and lower portions.
• Key components include the mouth, esophagus, stomach (fundus, cardia, body, pylorus), mucosal and parietal cells, chief cells (pepsinogen), endocrine cells (gastrin), small intestine (duodenum, jejunum, ileum), large intestine (cecum, ascending, transverse, descending, sigmoid colon, rectum), and the importance of pancreas, liver, and gallbladder in digestion.

Physiology of the GI Tract

• The purpose of the GI tract is ingestion, digestion, and absorption.
• Key categories of nutrients include carbohydrates (digested by amylase in the oral cavity and pancreas; enzymes from the brush border), proteins (digested in the duodenum with gastrin and hydrochloric acid converting pepsinogen to pepsin; chyme); and lipids (digested by cholecystokinin stimulating bile and pancreatic lipase).

Peptic Ulcers

• Peptic ulcers are breaks in the mucosa of the stomach or duodenum, potentially leading to perforation.
• Duodenal and gastric ulcers are commonly caused by Helicobacter pylori.
• This bacterium stimulates inflammation, increases hydrochloric acid production, and causes urease production.
• Transmission occurs through person-to-person contact, fecal-oral route, or contaminated food.
• Laboratory tests include gastroscopy, breath tests, stool antigen tests, and serological tests.

GI Ulcers - Diagnosis

• Gastroscopy with tissue samples using rapid urease tests (phenol red color change) and microbiological cultures.
• Histological tests, high sensitivity and specificity (94% and 98%) urea breath tests (using carbon-13 labeled urea), and commonly used tests (noninvasive). Pathogenic H. pylori produces urease breaking down urea and releasing CO2.
• Elevated labeled CO2 indicates H. pylori presence.
• These tests help in detecting active infections and monitoring treatment.

Stool tests for H. pylori antigen

• Stool tests are reliable, convenient, noninvasive tests for H. pylori antigen detection.
• They have high sensitivity and specificity (typically >90%) and can detect active and recent infections.
• Immunoassays, like ELISA, are used for this testing.

Zollinger-Ellison Syndrome

• Associated with benign, non-beta islet cell, gastrin-secreting tumors (gastrinomas).
• Gastrinomas typically occur in the pancreas or duodenum.
• They stimulate excess hydrochloric acid.
• Symptoms include gastric pain, peptic ulcers (often fulminant), massive gastric hypersecretion, hypergastrinemia, diarrhea, and steatorrhea.

Zollinger-Ellison Syndrome- Diagnosis

• Gastrin levels are measured using immunoassay techniques (elevated gastrin levels and high gastric acid levels indicate a gastrinoma).
• Imaging techniques (CT scan) are used for diagnosis.
• Gastroscopy is used in diagnosis.
• H. pylori tests are often negative.

Malabsorption Syndrome

• Malabsorption syndrome involves defective nutrient absorption, potentially affecting all or specific nutrients.
• Single nutrient malabsorption, like lactase deficiency, leads to lactose excretion.
• Widespread deficiencies involve conditions like Crohn's disease and celiac disease.
• Common symptoms include diarrhea, abdominal discomfort, and weight loss.

Malabsorption Syndrome - Diagnosis

• Diagnostic tests include a complete blood count (CBC), prothrombin time, vitamin and mineral assays, serologic tests (e.g., for celiac disease), pancreatic elastase-1, stool cultures (for bacteria and parasites), fecal fat tests, and lactose tolerance tests.

Diarrhea

• Diarrhea is characterized by loose, watery, and frequent stools.
• Acute diarrhea is caused by bacterial, parasitic, or viral infections, or antibiotics.
• Chronic diarrhea often lasts more than 4 weeks.
• Chronic conditions that can cause diarrhea include inflammatory bowel disease (IBD), irritable bowel syndrome, celiac disease, food intolerance (e.g., lactose), and chemotherapy or radiation therapy.
• Diarrhea can lead to dehydration and low serum potassium levels.

Laboratory Tests for Diarrhea

• Stool cultures identify bacteria, viruses, or parasites.
• Immunoassays are used to check for specific pathogens like C. difficile, rotavirus, or E. coli strains.
• A fecal fat test can help assess malabsorption.

Inflammatory Bowel Disease (IBD)

• IBD is an unknown cause (autoimmune, genetic, medication, or infectious agents) characterized by bouts of remission and exacerbations.
• Common types include ulcerative colitis and Crohn's disease, both causing abdominal pain, cramping, anorexia, bloody diarrhea, and anemia.

Crohn's Disease X Ulcerative Colitis

• Crohn's disease and ulcerative colitis are differentiated by the location of inflammation, stool characteristics, granuloma presence, and malabsorption.
• Crohn's disease frequently affects the terminal ileum and colon, manifesting as loose semiformed stools.
• Ulcerative colitis mostly affects the rectum and colon, presenting with frequent watery stools containing mucus and blood.

Inflammatory Bowel Disease - Diagnosis

• Diagnostic tests for IBD involve C-reactive protein, calprotectin stool tests, fecal examination (red and white blood cells), occult blood tests, and imaging (e.g., MRI) with endoscopy/biopsy.

Celiac Disease

• Celiac disease is an autoimmune disorder triggered by gluten intolerance.
• It manifests as inflammation and malabsorption.
• A gluten-free diet is crucial for managing the condition.
• Clinical features include signs, symptoms, biopsy (gold standard, invasive, endoscopy, villus atrophy), and serological tests like IgA anti-endomysial antibody (EMA), IgA antigliadin antibody (AGA), IgA anti-tissue transglutaminase antibody (tTG), and IgA-deamidated gliadin peptide antibody (DGP).

Gastrointestinal Function Tests

• Tests assess digestive system function, identifying abnormalities in conditions like pancreatitis, celiac disease, and cystic fibrosis. Tests include fecal fat tests (e.g., Sudan stain), 72-hour stool collection, 24-hour pH monitoring, D-xylose absorption tests, and evaluating absorption in the intestines.