137. Constipation and diarrhea - etiology, pathogenesis, clinical manifestations.

Constipation and diarrhea – etiology, pathogenesis, and clinical manifestations.

Constipation is infrequent or difficult evacuation of stools, typically defined as fewer than three bowel movements per week, or straining/ hard stools.

Etiology

Functional (most common)

• Low- fiber diet.
• Low fluid intake.
• Sedentary lifestyle.
• Habitual stool suppression.

Secondary causes

• Medications: opioids, anticholinergics, calcium channel blockers, iron supplements.
• Metabolic/endocrine: hypothyroidism, hypercalcemia, diabetes mellitus.
• Neurological: Parkinson’s disease, spinal cord injury.
• Obstructive lesions: colorectal cancer, strictures.

Pathogenesis

• Decreased intestinal motility → prolonged transit time → excessive water reabsorption → hard, dry stools.
• Obstructive or mechanical causes impede stool passage.
• Neurological dysfunction may impair reflexes involved in defecation.

Clinical manifestations

• Infrequent bowel movements.
• Straining during defecation.
• Hard, lumpy stools.
• Sensation of incomplete evacuation.
• Abdominal discomfort or bloating.
• Possible complications: hemorrhoids, anal fissures, fecal impaction.

Diarrhea

Diarrhea is increased frequency and liquidity of stools, usually defined as >3 loose or liquid stools per day.

Etiology

Infectious

• Viruses: rotavirus, norovirus.
• Bacteria: E. coli, Salmonella, Shigella, Vibrio cholerae.
• Parasites: Giardia lamblia, Entamoeba histolytica.

Non- infectious

• Food intolerance (e.g., lactose intolerance).
• Inflammatory bowel disease (ulcerative colitis, Crohn’s).
• Irritable bowel syndrome.
• Malabsorption syndromes (celiac disease).
• Endocrine causes: hyperthyroidism.

Pathogenesis

1. 1 Osmotic diarrhea

• Non-absorbed solutes (e.g., lactose in lactose intolerance) draw water into the lumen.
• Stops when fasting.

1. 2 Secretory diarrhea

• Active secretion of electrolytes and water into the lumen (e.g., cholera toxin activates adenylate cyclase).
• Large volume, persists during fasting.

1. 3 Exudative/inflammatory diarrhea

• Mucosal damage → exudation of plasma proteins, blood, mucus (e.g., ulcerative colitis, infections with Shigella).

1. 4 Increased motility

• Accelerated transit (e.g., irritable bowel syndrome) reduces absorption time.

Clinical manifestations

• Frequent, loose, or watery stools.
• Abdominal cramps.
• Urgency, tenesmus (especially in colitis).
• Dehydration: dry mouth, hypotension, tachycardia.
• Weight loss (chronic cases).
• Electrolyte disturbances ( hypokalemia, metabolic acidosis).