Human Health and Disease

NCERT Line-by-Line Breakdown for NEET 2026

Unit 3: Biology in Human Welfare

Health does not simply mean ‘absence of disease’. It is a state of complete physical, mental, and social well-being (WHO). Good health increases productivity and economic prosperity. Diseases are broadly grouped into Infectious (transmittable) and Non-infectious.

1. Common Diseases in Humans

A. Bacterial Diseases

Disease	Pathogen	Organs Affected & Symptoms	Key Test/Note
Typhoid	Salmonella typhi	Small intestine. Sustained high fever (39-40°C), stomach pain, constipation. Intestinal perforation in severe cases.	Widal Test. Mary Mallon (Typhoid Mary).
Pneumonia	Streptococcus pneumoniae, Haemophilus influenzae	Alveoli (fill with fluid). Fever, chills, cough. Lips/nails turn gray to bluish.	Transmitted by droplets/aerosols.

B. Viral Diseases

Common Cold: Caused by Rhinoviruses. Infects nose and respiratory passage but NOT lungs. Lasts 3-7 days.

C. Protozoan Diseases

🦟 Malaria (Plasmodium):

Vector: Female Anopheles mosquito.
Species: P. vivax, P. malariae, P. falciparum (Malignant/Fatal).
Life Cycle: Sporozoites (Infectious form) injected → Liver (multiplication) → RBCs (rupture releases Haemozoin causing chills/fever) → Gametocytes formed → Mosquito gut (Fertilization) → Salivary glands.

Amoebiasis (Amoebic Dysentery): Entamoeba histolytica. Large intestine. Stool with excess mucus and blood clots. Vector: Houseflies.

D. Helminthic & Fungal Diseases

Ascariasis: Ascaris (Roundworm). Internal bleeding, muscular pain, blockage of intestinal passage.
Elephantiasis (Filariasis): Wuchereria (Filarial worm). Chronic inflammation of lymphatic vessels of lower limbs. Vector: Culex mosquito.
Ringworm: Microsporum, Trichophyton, Epidermophyton. Dry, scaly lesions. Thrives in heat and moisture.

2. Immunity

A. Innate Immunity (Non-specific)

Present at birth. Four types of barriers:

Physical: Skin, Mucus coating (Respiratory, GI, Urogenital tracts).
Physiological: Acid in stomach, Saliva in mouth, Tears.
Cellular: PMNL-neutrophils, Monocytes, Natural Killer (NK) cells, Macrophages (Phagocytosis).
Cytokine: Virus-infected cells secrete Interferons (Protect non-infected cells).

B. Acquired Immunity (Specific)

Pathogen specific. Characterized by Memory.

Humoral Immune Response: B-lymphocytes produce Antibodies into blood.
Cell-mediated Immune Response (CMI): T-lymphocytes. Responsible for Graft Rejection.

🛡️ Antibody Structure (H2L2):
4 peptide chains: 2 Light chains, 2 Heavy chains.
IgA: Present in Colostrum (Mother’s milk).
IgE: Allergic reactions.
IgG: Can cross placenta.

C. Active vs Passive Immunity

Active: Host produces antibodies (Vaccination, Natural infection). Slow but long-lasting.
Passive: Ready-made antibodies given (Anti-tetanus serum, Colostrum). Fast but short-lived.

D. Immune System Disorders

Allergy: Exaggerated response to antigens (allergens). IgE antibodies produced. Release of Histamine and Serotonin from Mast cells. Treatment: Antihistamine, Adrenaline, Steroids.
Autoimmunity: Body attacks self-cells. Example: Rheumatoid Arthritis.

E. Lymphoid Organs

Primary: Bone Marrow (B & T cells originate; B mature) & Thymus (T cells mature).
Secondary: Spleen (Graveyard of RBCs), Lymph nodes, MALT (Mucosa-associated lymphoid tissue – constitutes 50%).

3. AIDS & Cancer

AIDS (Acquired Immuno Deficiency Syndrome)

Caused by HIV (Human Immunodeficiency Virus) – a Retrovirus.
Mechanism: Virus attacks Helper T-lymphocytes (T_H) → T_H count decreases drastically → Person becomes immune-deficient.
Test: ELISA (Enzyme Linked Immuno-Sorbent Assay).

Cancer

Normal cells show Contact Inhibition (contact with other cells inhibits uncontrolled growth). Cancer cells lose this property.

Benign Tumors: Confined to original location.
Malignant Tumors: Mass of proliferating cells (Neoplastic cells). Show Metastasis (spread to other parts via blood).
Carcinogens: Physical (X-rays, UV), Chemical (Tobacco smoke), Biological (Oncoviruses).
Treatment: Surgery, Radiation, Chemotherapy. Alpha-interferon (Biological response modifier).

4. Drugs and Alcohol Abuse

Category	Source Plant	Examples	Effects
Opioids	Poppy plant (Papaver somniferum) – Latex.	Morphine, Heroin (Smack/Diacetylmorphine).	Bind to receptors in CNS & GIT. Depressant, slows body functions.
Cannabinoids	Cannabis sativa (Hemp).	Marijuana, Hashish, Charas, Ganja.	Receptors in Brain. Effects Cardiovascular system.
Coca Alkaloid	Erythroxylum coca.	Cocaine (Coke/Crack).	Interferes with Dopamine transport. Euphoria, increased energy.

Hallucinogens: Atropa belladonna and Datura.
Tobacco: Nicotine stimulates Adrenal gland → Adrenaline (High BP, Heart rate).

Adolescence & Addiction: Repeated use leads to increased tolerance level of receptors.
Cirrhosis: Long-term alcohol abuse damages the liver.

📝 Rapid Fire MCQs

Q1. Widal test is used for the diagnosis of:

A) Malaria
B) Pneumonia
C) Typhoid
D) Tuberculosis

Click to check Answer

Answer: C) Typhoid.

Q2. Which antibody is abundant in colostrum?

A) IgG
B) IgM
C) IgE
D) IgA