Nature of Disease: Causes, Effects & Cellular Changes
A PEBC-oriented guide.
1. What Is a Disease? (The Real Definition)
In pathology terms, disease is not just “feeling sick.”
It is a deviation from normal structure or function of cells, tissues, or organs that leads to clinical signs and symptoms.
Think of it like this (corporate hat on 🧢):
Disease = System failure caused by internal or external risk factors, resulting in functional breakdown.
For PEBC, always remember:
- Disease starts at the cellular level
- Clinical symptoms come later
- Structure + function = inseparable duo
2. Nature of Disease (How Disease Behaves)
Diseases are classified based on origin, duration, and progression.
A. Based on Cause (Etiology)
- Congenital – present at birth (e.g., genetic defects)
- Acquired – develop after birth (e.g., infections, lifestyle diseases)
B. Based on Duration
- Acute – rapid onset, short duration (e.g., acute infection)
- Chronic – slow progression, long duration (e.g., diabetes, hypertension)
C. Based on Spread
- Localized – affects one area (e.g., abscess)
- Systemic – affects whole body (e.g., septicemia)
📌 PEBC Tip: Always link nature of disease with pathogenesis (sequence of events from cause → effect).
3. Causes of Disease (Etiology)
This is PEBC gold. Causes are broadly divided into:
1. Genetic Causes
- Gene mutations
- Chromosomal abnormalities
👉 Example: Sickle cell anemia
2. Infectious Agents
- Bacteria
- Viruses
- Fungi
- Parasites
👉 Example: Tuberculosis
3. Physical Agents
- Trauma
- Heat, cold
- Radiation
- Electricity
4. Chemical Agents & Drugs
- Poisons
- Environmental toxins
- Drug toxicity (high-yield for pharmacists)
5. Nutritional Imbalance
- Deficiency (e.g., vitamin C → scurvy)
- Excess (e.g., obesity-related disorders)
6. Immunological Causes
- Autoimmune diseases
- Hypersensitivity reactions
🧠 Tell-it-like-it-is moment:
Most diseases are multifactorial. PEBC loves questions where two or more causes interact.
4. Effects of Disease on the Body
Diseases don’t just exist—they disrupt.
Effects can be:
- Local effects – inflammation, tissue damage
- Systemic effects – fever, fatigue, weight loss
- Functional effects – reduced organ performance
- Psychological effects – stress, anxiety (often ignored, but real)
📌 Example:
Chronic kidney disease →
Structural damage (nephrons) →
Functional loss (filtration) →
Systemic effects (uremia, electrolyte imbalance)
That cause-effect chain is PEBC thinking.
5. Cellular Adaptations: Survival Mode of Cells
Before cells die, they adapt. This is crucial.
A. Hypertrophy
- Increase in cell size
👉 Example: cardiac muscle in hypertension
B. Hyperplasia
- Increase in cell number
👉 Example: endometrial hyperplasia
C. Atrophy
- Decrease in cell size
👉 Example: muscle wasting
D. Metaplasia
- One mature cell type replaced by another
👉 Example: respiratory epithelium in smokers
📌 Classic PEBC trap:
Adaptation ≠ injury
Adaptation is reversible.
6. Cell Injury: When Adaptation Fails
A. Reversible Cell Injury
- Cell swelling
- Fatty change
- Mitochondrial dysfunction
B. Irreversible Cell Injury
Leads to cell death.
Types of Cell Death:
-
Necrosis
- Uncontrolled
- Inflammatory response
- Always pathological
-
Apoptosis
- Programmed cell death
- No inflammation
- Can be physiological or pathological
🧠 Memory hack:
Necrosis = noisy death
Apoptosis = silent exit
7. Structural & Functional Alterations (The Core Idea)
Every disease causes:
- Structural changes → seen under microscope
- Functional changes → seen clinically
And here’s the punchline PEBC wants you to internalize:
Structure determines function.
Damage the structure → function collapses.
Example:
- Liver cirrhosis
- Structural: fibrosis, nodules
- Functional: reduced detoxification, protein synthesis
8. Why This Topic Is Critical for PEBC
This chapter:
- Builds clinical reasoning
- Connects pathology with pharmacotherapy
- Helps understand why drugs work or fail
- Is tested indirectly through case-based MCQs
Old books taught it slowly. Modern exams expect it instantly.
Final Takeaway (Bookmark This)
Disease is not random chaos.
It is a logical biological process:
Cause → Cellular change → Structural damage → Functional loss → Clinical disease