GIT II disease Bowel Disease

🧠 OVERVIEW: What is Inflammatory Bowel Disease (IBD)?

Inflammatory Bowel Disease (IBD) = a chronic (long-term) inflammation of the intestines

There are 2 main types:

  1. Crohn’s disease

  2. Ulcerative colitis

👉 The difference between them is mainly:

  • Where in the GI tract they occur

  • How deep the inflammation goes

🧱 BASIC ANATOMY YOU MUST KNOW

The intestinal wall has 4 layers:

  1. Mucosa (inner layer, absorbs nutrients)

  2. Submucosa

  3. Muscularis externa

  4. Serosa (outer layer)

👉 This matters because:

  • Ulcerative colitis → affects mucosa + submucosa only

  • Crohn’s disease → affects ALL layers (transmural)

🧬 AETIOLOGY (CAUSES OF IBD)

👉 Key idea: The exact cause is unknown (idiopathic)
But we think it is due to a combination of:

1. 🧬 Genetic factors

  • Over 240 genes linked to IBD

  • Important gene: NOD2

    • Normally detects bacteria

    • Helps control immune response

👉 Problem:

  • Mutation → overactive immune response

2. 🦠 Gut microbiota (bacteria in your gut)

  • Your gut contains trillions of bacteria

  • They are normally helpful

👉 Problem:

  • Immune system reacts abnormally to normal bacteria

  • Causes chronic inflammation

3. 🌍 Environmental factors

Things that increase risk:

  • Processed foods, high sugar

  • Low fibre diet

  • Industrialised lifestyle

Other factors:

  • Smoking:

    • Worse for Crohn’s

    • May protect ulcerative colitis

  • Stress → worsens both

  • Appendix removal:

    • ↑ Crohn’s risk

    • ↓ ulcerative colitis risk

4. 🛡 Immune system dysfunction

👉 The BIGGEST factor

Normally:

  • Immune system responds appropriately

In IBD:

  • Immune system becomes overactive

  • Attacks the intestine itself

⚙ PATHOGENESIS (WHAT ACTUALLY HAPPENS)

Let’s break this down simply 👇

Step 1: Barrier breakdown

  • Intestinal lining (epithelium) becomes damaged

  • Gaps form → bacteria leak through

Step 2: Immune system activation

  • Bacteria trigger immune cells

  • Dendritic cells present antigens to T cells

Step 3: T helper cell activation

T helper cells (CD4+) become activated and differentiate into:

  • TH1 → Crohn’s disease

  • TH2 → Ulcerative colitis

👉 These cells release cytokines (chemical signals)

Step 4: Excess inflammation

  • Too many cytokines → excessive inflammation

  • Causes:

    • Tissue damage

    • Ulcers

    • Loss of function

Step 5: Chronic cycle

  • Damage → more immune activation → more damage

👉 This creates a chronic relapsing disease

🔍 CROHN’S DISEASE

📍 Where does it occur?

  • Anywhere in GI tract (mouth → anus)

  • Common: terminal ileum

🔬 Pathology (what it looks like)

  • Transmural inflammation (all layers)

  • Skip lesions (patchy disease)

  • “Cobblestone” appearance

  • Granulomas (hallmark)

⚠ Clinical Manifestations

🔹 GI symptoms

  • Diarrhoea (sometimes bloody)

  • Abdominal pain

  • Fever

🔹 Malabsorption

  • Nutrient deficiency

  • Weight loss

  • Low protein (hypoalbuminemia)

🔹 Complications

  • Strictures (narrowing)

  • Fistulas (abnormal connections)

  • Perforation → infection

  • Abscesses

🔹 Cancer risk

  • Increased risk of adenocarcinoma

🔹 Disease pattern

  • Relapsing-remitting

    • Flare-ups + symptom-free periods

🔍 ULCERATIVE COLITIS

📍 Where does it occur?

  • Only in:

    • Colon

    • Rectum

🔬 Pathology

  • Only mucosa + submucosa

  • Continuous inflammation (no skip lesions)

  • Starts at rectum → spreads upward

⚠ Clinical Manifestations

🔹 GI symptoms

  • Bloody diarrhoea

  • Mucus in stool

  • Lower abdominal pain

🔹 Severe complication: TOXIC MEGACOLON

  • Colon becomes massively dilated

  • Can rupture → life-threatening

Signs:

  • Fever

  • Tachycardia

  • Low blood pressure

🔹 Cancer risk

  • Increased risk of colon cancer

🔹 Disease pattern

  • Also relapsing-remitting

⚖ KEY DIFFERENCES (IMPORTANT FOR EXAMS)

Feature

Crohn’s

Ulcerative Colitis

Location

Anywhere

Colon only

Pattern

Skip lesions

Continuous

Depth

Transmural

Superficial

Granulomas

Yes

No

Diarrhoea

± blood

Bloody

Complications

Fistulas, strictures

Toxic megacolon

🌍 EXTRA-INTESTINAL MANIFESTATIONS

👉 IBD affects other organs too

Examples:

🦴 Joints

  • Arthritis (very common)

🧴 Skin

  • Erythema nodosum (red lumps on legs)

👁 Eyes

  • Uveitis (inflammation)

🫁 Lungs

  • Pneumonitis

🩸 Blood

  • Increased clot risk

🧪 DIAGNOSIS

Tests:

  • Colonoscopy / endoscopy

  • Imaging (X-ray, CT)

  • Faecal calprotectin

    • Marker of inflammation

👉 Helps distinguish from IBS (which is NOT inflammatory)

🧠 SIMPLE SUMMARY (REMEMBER THIS)

👉 IBD = immune system attacking the gut

  • Cause = genetics + environment + immune dysfunction

  • Leads to = chronic inflammation

  • Two types:

    • Crohn’s → patchy, deep, anywhere

    • UC → continuous, superficial, colon only