08.2 Distal tract pathologies

Distal GI Tract Pathologies

• This lecture covers distal gastrointestinal tract anatomy, physiology, and pathologies.
• Key topics include diarrhea, constipation, appendicitis, diverticulosis, diverticulitis, and anal disorders.
• The lecture emphasizes understanding pathophysiology, clinical presentations, diagnostics, and treatment approaches.

Learning Objectives

• Differentiate osmotic and secretory diarrhea mechanisms and causes.
• Explain constipation causes and physiological mechanisms, relating it to fiber intake, fluid, and motility.
• Describe acute appendicitis anatomy, etiology, pathophysiology, and presentation.
• Compare and contrast diverticulosis and diverticulitis, including complications.
• Explain the role of GI anatomy in pathologies like hemorrhoids and rectal fissures, differentiating causes of hematochezia and melena.

Key Concepts and Definitions

• Diarrhea: Frequent loose or watery stools (more than three times a day) lasting less than two weeks. It can be caused by excessive water in stools from disrupted absorption or increased secretion.
• Osmotic Diarrhea: Occurs when solutes in the intestines retain water. Examples include lactose intolerance and celiac disease.
• Secretory Diarrhea: Occurs when ion secretion (e.g., chloride) is increased by toxins or other stimuli, drawing water out of cells. Often seen in infections.
• Constipation: Infrequent, hard, lumpy stools, difficulty passing stools, or feelings of incomplete evacuation. Common causes include low fiber intake, dehydration, and reduced motility.
• Normal Transit Constipation: Linked to psychological factors or low activity levels.
• Slow Transit Constipation: Reduced motility due to fewer pacemaker cells (interstitial cells of Cajal).
• Appendicitis: Inflammation of the appendix, often caused by blockage (e.g., fecalith or lymphoid hyperplasia). Classic symptoms include peri-umbilical pain migrating to the right lower quadrant (RIF).
• Diverticulosis: Outpouchings in the colon's mucosa and submucosa. Commonly asymptomatic and linked to low-fiber diets and high pressure in the sigmoid colon.
• Diverticulitis: Inflammation of diverticula, typically due to trapped stool and bacterial invasion. Symptoms include pain in the lower left quadrant, fever, bloating, and possibly bloody stools (hematochezia).

Clinical Applications

• Diarrhea often presents with increased frequency and urgency.
• Osmotic diarrhea can be treated by ceasing the offending substance (e.g., lactose).
• Constipation management includes high-fiber diets and sufficient hydration.
• Classic appendicitis presentation is right lower quadrant pain. However, atypical presentations are more common, especially in children and pregnant individuals.

Pathophysiology

• Osmotic Diarrhea: Results from poorly absorbed substances, retaining water in the intestines (e.g., lactose intolerance).
• Secretory Diarrhea: Driven by abnormal ion transport, leading to excessive water secretion into the lumen (e.g., infections like cholera).
• Normal Colonic Water Reabsorption: Typically 99% of water is reabsorbed in the colon. Failure of this can lead to watery stools.
• Constipation Mechanisms: Can be either slow transit (reduced peristalsis) or impacted by bulk and fluid interactions.
• Stress and age affect transit times.
• Appendicitis Mechanisms: Obstruction, pressure, impaired blood flow leading to bacterial invasion.

Differential Diagnosis

• Diarrhea can be caused by infections, malabsorption, IBS, and diabetes.
• Constipation has functional and obstructive causes.

Investigations

• Stool analysis is useful to determine possible pathogens and presence of blood or mucus.
• Electrolyte levels are crucial in severe diarrhea cases, as they detect dehydration.
• Imaging (CT/abdominal X-ray) is helpful in suspecting obstructions.
• Transit studies measure stool movement.
• Physical examination and imaging (e.g., CT or ultrasound) are used in appendicitis evaluations.

Test your knowledge on gastrointestinal disorders with this quiz. Explore key characteristics of conditions like functional constipation and diarrhea, as well as critical investigations and imaging techniques like those used for appendicitis. Perfect for medical students or anyone interested in digestive health.