Human Health and Disease — Immunity Made Simple
Master NEET's Human Health and Disease — common pathogens and their vectors, innate vs acquired immunity, active vs passive immunity, antibodies, allergies and vaccination, with worked examples.
By the PadhoDost Team · 📖 7 min read · Updated 4 August 2026
Part of NEET (Medical) prep🧠 A fortress with layered defences
Think of your body as a walled fortress. The outer wall and moat — your skin, mucus and stomach acid — stop most invaders without asking who they are. But if an enemy slips inside, a trained intelligence unit steps in: it identifies that specific enemy, defeats it, and keeps a 'wanted poster' so it can crush the same enemy instantly next time. That two-layer defence is exactly how your immune system works.
Health is not merely the absence of disease but a state of complete physical, mental and social well-being. Diseases are often caused by pathogens — disease-causing organisms like bacteria, viruses, fungi, protozoans and worms (helminths). Your immune system fights them using two arms: innate (inborn, general) immunity and acquired (specific, memory-based) immunity.
Common human diseases you must know
| Disease | Pathogen (type) | How it spreads / organ affected |
|---|---|---|
| Typhoid | Salmonella typhi (bacterium) | Contaminated food/water; small intestine (Widal test) |
| Pneumonia | Streptococcus pneumoniae (bacterium) | Droplets; alveoli of the lungs |
| Common cold | Rhinoviruses | Droplets; nose and respiratory passage |
| Malaria | Plasmodium (protozoan) | Female Anopheles mosquito; liver and RBCs |
| Amoebiasis | Entamoeba histolytica (protozoan) | Houseflies carry it; large intestine |
| Filariasis | Wuchereria (helminth) | Female Culex mosquito; lymphatic vessels |
| Ringworm | Microsporum / Trichophyton (fungi) | Contact; skin, nails and scalp |
Two lines of defence: innate vs acquired immunity
Innate immunity is present from birth and is non-specific — physical barriers (skin), physiological barriers (acid, saliva), cellular barriers (phagocytes) and inflammation attack anything foreign. Acquired immunity is specific and develops after exposure. It is run by lymphocytes: B-cells produce antibodies (humoral / antibody-mediated immunity), while T-cells drive cell-mediated immunity. Its superpower is memory — it responds faster and stronger on a second exposure.
| Feature | Active immunity | Passive immunity |
|---|---|---|
| Source | Body makes its own antibodies | Ready-made antibodies given from outside |
| Trigger | Infection or vaccine (antigen) | Injected serum or mother's antibodies |
| Speed | Slow to appear | Acts immediately |
| Duration | Long-lasting (has memory) | Short-lived (no memory) |
| Example | Chickenpox recovery, vaccines | Colostrum, anti-tetanus serum (ATS), anti-venom |
📝 Spot the immunity type
A newborn receives antibodies through mother's first milk (colostrum) -> ready-made antibodies -> Passive immunity.
A child recovers from measles and is protected for life -> body made its own memory cells -> Active (natural).
A student is given a tetanus vaccine and slowly builds antibodies -> Active (artificial).
A dog-bite victim is injected with pre-formed anti-tetanus serum -> Passive (artificial).
Remember these
- ✓Pathogens include bacteria, viruses, fungi, protozoans and helminths.
- ✓Innate immunity is non-specific and present from birth; acquired immunity is specific and remembers.
- ✓B-lymphocytes give humoral (antibody-mediated) immunity; T-lymphocytes give cell-mediated immunity.
- ✓Active immunity is slow but long-lasting; passive immunity is fast but temporary.
- ✓Vaccination creates memory cells (primary response) so a later infection triggers a fast, strong secondary response.
- ✓Immune disorders include allergies (IgE), autoimmunity (body attacks self, e.g. rheumatoid arthritis) and AIDS (HIV destroys helper T-cells).
⚡ Quick check
Which class of antibodies is responsible for allergic reactions such as hay fever and asthma?
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