The Human Bowel: Anatomy, Physiology, Disorders & Treatment Guide

1. Introduction

• The bowel (intestines) is a vital part of the digestive system, responsible for nutrient absorption, waste processing, and microbiome regulation.
• It consists of the small intestine and large intestine (colon, rectum, and anus).
• Common bowel disorders include irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), constipation, diarrhoea, and colorectal cancer.

2. Anatomy of the Bowel

• Small Intestine:
  • Duodenum: Initial segment where digestion begins.
  • Jejunum: Main site for nutrient absorption.
  • Ileum: Absorbs vitamins and bile salts.
• Large Intestine (Colon):
  • Ascending, Transverse, Descending, and Sigmoid Colon: Absorb water and electrolytes.
• Rectum & Anus:
  • Rectum: Stores stool before elimination.
  • Anus: Controls waste expulsion.

3. Physiology of the Bowel

• Digestion & Absorption:
  • Carbohydrates, proteins, and fats are broken down by enzymes and absorbed.
• Water & Electrolyte Balance:
  • Small intestine absorbs nutrients; colon absorbs water and minerals.
• Microbiome Function:
  • Trillions of gut bacteria aid in digestion, immune function, and vitamin production.
• Peristalsis & Motility:
  • Smooth muscle contractions move food and waste through the intestines.

4. Common Disorders & Pathophysiology

A. Irritable Bowel Syndrome (IBS)

• Cause: Abnormal gut-brain interaction.
• Symptoms: Abdominal pain, bloating, alternating constipation/diarrhoea.

B. Inflammatory Bowel Disease (IBD)

• Types:
  • Crohn’s Disease: Inflammation of any part of the bowel.
  • Ulcerative Colitis: Inflammation of the colon and rectum.
• Symptoms: Chronic diarrhoea, bloody stool, weight loss, fatigue.

C. Constipation

• Cause: Slow bowel movement, low fibre, dehydration.
• Symptoms: Straining, hard stools, infrequent bowel movements.

D. Diarrhoea

• Cause: Infections, food intolerance, IBS, or IBD.
• Symptoms: Frequent, loose, watery stools.

E. Colorectal Cancer

• Cause: Uncontrolled growth of abnormal cells in the colon.
• Risk Factors: Age, family history, diet, smoking, obesity.

F. Celiac Disease (Gluten Intolerance)

• Cause: Autoimmune reaction to gluten damaging the small intestine.
• Symptoms: Diarrhoea, bloating, malnutrition, weight loss.

G. Diverticulosis & Diverticulitis

• Cause: Small pouches (diverticula) form in the colon; inflammation causes diverticulitis.
• Symptoms: Abdominal pain, fever, constipation, or diarrhoea.

H. Bowel Obstruction

• Cause: Physical blockage (tumour, adhesions) or functional paralysis (ileus).
• Symptoms: Severe abdominal pain, vomiting, no bowel movements.

5. Signs & Symptoms of Bowel Disorders

• Early Symptoms:
  • Bloating, gas, abdominal discomfort.
  • Irregular bowel movements.
• Advanced Symptoms:
  • Severe diarrhoea or constipation.
  • Blood in stool (red flag for cancer or IBD).
• Red Flags:
  • Unexplained weight loss, severe pain, persistent rectal bleeding.

6. When to See a Doctor

• Persistent constipation or diarrhoea (lasting over 3 weeks).
• Abdominal pain that disrupts daily activities.
• Unexplained weight loss or blood in stool.

7. Emergency Signs Requiring Immediate Care

• Severe, sudden abdominal pain (possible obstruction or perforation).
• Profuse bleeding in stool.
• Inability to pass gas or stool (sign of bowel obstruction).

8. Diagnostic Process

• Clinical Examination: Palpation for tenderness, bloating, rectal exam.
• Laboratory Tests:
  • Stool test: Checks for infections, blood, or parasites.
  • Celiac panel: Tests for gluten intolerance.
• Imaging Tests:
  • Colonoscopy: Examines the colon for polyps, inflammation, or cancer.
  • CT Scan/MRI: Detects bowel obstruction, Crohn’s disease.
• Specialist Procedures:
  • Biopsy: Confirms IBD, celiac disease, or cancer.
  • Barium Enema: X-ray imaging of the colon.

9. Likely Diagnoses

• IBS or IBD (Crohn’s or Ulcerative Colitis).
• Constipation or Chronic Diarrhoea.
• Celiac Disease.
• Colorectal Cancer.

10. Treatment Options

A. Medications

• For IBS:
  • Antispasmodics (Hyoscine, Mebeverine).
  • Fibre supplements (Psyllium husk).
• For IBD:
  • Aminosalicylates (Mesalazine, Sulfasalazine).
  • Immunosuppressants (Azathioprine, Biologics).
• For Constipation:
  • Laxatives (Polyethylene Glycol, Bisacodyl).
• For Diarrhoea:
  • Antidiarrheals (Loperamide, Bismuth Subsalicylate).
• For Colorectal Cancer:
  • Chemotherapy (Fluorouracil, Capecitabine).
• Approximate Medication Costs (USD):
  • IBS Medications: $10–$100 per month.
  • IBD Immunosuppressants: $500–$5,000 per month.
  • Laxatives & Antidiarrheals: $5–$50 per month.

B. Surgical/Procedural Interventions

• Bowel Resection (For IBD, Cancer) ($10,000–$50,000).
• Colostomy/Ileostomy (For Severe Disease) ($20,000–$60,000).
• Polypectomy (For Colon Polyps) ($3,000–$8,000).

C. Lifestyle Modifications & Home Remedies

• For IBS & Constipation:
  • High-fibre diet (vegetables, whole grains).
  • Hydration & regular exercise.
• For IBD:
  • Low-fibre, anti-inflammatory diet.
  • Probiotics to support gut bacteria.
• For Colorectal Cancer Prevention:
  • Avoid processed meats, eat fibre-rich foods, get regular screening.

11. Precautions & Prevention

• Eat a balanced diet rich in fibre and probiotics.
• Stay hydrated and avoid excessive alcohol or processed foods.
• Regular colonoscopies after age 45 (or earlier if high risk).
• Manage stress, as gut health is linked to mental well-being.

12. Prognosis & Recovery

• IBS: Chronic but manageable with diet & lifestyle changes.
• IBD: Requires long-term treatment; remission is possible.
• Constipation & Diarrhoea: Resolves with diet & medications.
• Colorectal Cancer: Early detection improves survival rates.

13. Cost of Treatment

• Colonoscopy: $1,000–$3,000.
• IBD Treatment: $500–$5,000 per month.
• Colorectal Cancer Surgery & Chemotherapy: $50,000+.

14. Frequently Asked Questions (FAQs)

1. What foods help digestion? – Fibre, fermented foods, probiotics.
2. How often should I have a bowel movement? – 3 times/day to 3 times/week is normal.
3. Can stress affect bowel function? – Yes, gut health is linked to mental health.
4. What are the warning signs of colon cancer? – Blood in stool, weight loss, changes in bowel habits.
5. How do I prevent constipation? – Hydration, fibre, and exercise.