Human Health and Disease

Why This Chapter Matters

Human Health and Disease gives 5-8 marks in Class 12 boards. Immunity types, vaccines, pathogens, diseases, and drugs of abuse are all tested with direct factual questions.

Core Concepts

1. Health and Immunity

Innate (Non-specific) Immunity:

First line of defence — present at birth, doesn't require prior exposure.

Physical barriers: skin, mucus membranes, cilia.

Chemical barriers: lysozyme in tears/saliva, HCl in stomach, sebum.

Cellular: phagocytes (neutrophils, macrophages), NK cells, eosinophils.

Fever, inflammation: non-specific responses.

Acquired (Specific/Adaptive) Immunity:

Develops after exposure to antigen. Has memory.

Two types:

•Humoral: B-lymphocytes → plasma cells → antibodies (immunoglobulins IgA, IgD, IgE, IgG, IgM).

•Cell-mediated: T-lymphocytes → cytotoxic T-cells (kill infected cells). Crucial for graft rejection, virus-infected cells.

Active immunity: Body makes its own antibodies.

Natural active: after infection. Artificial active: vaccination (dead/weakened pathogen or toxoid).

Passive immunity: Ready-made antibodies given.

Natural passive: antibodies passed from mother to baby (through placenta or breast milk — colostrum rich in IgA).

Artificial passive: antiserum/antitoxin injected (snake venom treatment, tetanus antitoxin).

Memory cells: Long-lived B and T cells retained after primary response. Faster, stronger secondary response on re-exposure.

2. Lymphoid Organs

Primary lymphoid organs (where lymphocytes mature):

•Thymus: T-cells mature. Largest in childhood, involutes after puberty.

•Bone marrow: B-cells mature.

Secondary lymphoid organs (where immune responses occur):

•Spleen: filters blood, stores lymphocytes.

•Lymph nodes: filter lymph, initiate immune response.

•Tonsils, Peyer's patches (gut), MALT.

3. Common Diseases

Bacterial:

Typhoid: Salmonella typhi. Widal test. Fever, weakness.

Pneumonia: Streptococcus pneumoniae. Affects alveoli.

Tuberculosis: Mycobacterium tuberculosis. Lungs. BCG vaccine.

Cholera: Vibrio cholerae. Contaminated water.

Viral:

Common cold: Rhinovirus. Upper respiratory tract.

AIDS: HIV — retrovirus. Attacks T-helper (CD4⁺) cells. Depletes immunity.

HIV RNA → reverse transcriptase → DNA → integrates into host cell. ELISA/Western blot for diagnosis.

Dengue: Flavivirus. Aedes mosquito. Break-bone fever. Low platelet count.

Malaria: Plasmodium (protozoan). Anopheles mosquito.

P. vivax (benign tertian), P. falciparum (malignant tertian — most dangerous), P. malariae, P. ovale.

Protozoan:

Amoebiasis: Entamoeba histolytica. Contaminated food/water.

Filariasis (elephantiasis): Wuchereria bancrofti (nematode). Culex mosquito.

Ascariasis: Ascaris lumbricoides (roundworm). Soil → hand → mouth.

Fungal:

Ringworm: Microsporum, Trichophyton. Skin, nails, scalp.

4. Vaccines (Important List)

Disease	Vaccine	Pathogen

|---|---|---|

Smallpox	Vaccinia (cowpox virus) — first vaccine (Jenner 1796)	Variola virus
Tuberculosis	BCG (Bacillus Calmette-Guerin)	M. tuberculosis
Polio	OPV (oral, Sabin) or IPV (injected, Salk)	Poliovirus
Tetanus	Toxoid (inactivated tetanus toxin)	C. tetani
Rabies	Killed virus	Rabies virus
Hepatitis B	Recombinant (HBsAg in yeast)	Hepatitis B virus
DPT	Diphtheria toxoid + Pertussis + Tetanus toxoid	Combined

5. Cancer

Uncontrolled cell division. Benign (localised) vs Malignant (invades other tissues — metastasis).

Proto-oncogenes → Oncogenes (cause cancer). Tumour suppressor genes (e.g., p53) normally prevent cancer.

Causes: carcinogens (chemicals, radiation), viruses (oncogenic viruses), radiation.

Detection: biopsy, MRI, CT scan, tumour markers.

Treatment: Surgery, Radiotherapy, Chemotherapy, Immunotherapy.

6. Drugs and Alcohol Abuse

Opioids: Morphine, heroin (diacetylmorphine) from Papaver somniferum (opium poppy). Binds opioid receptors. Used as painkiller but highly addictive.

Cannabinoids: THC from Cannabis sativa (marijuana/ganja). Affects brain.

Cocaine: Alkaloid from Erythroxylum coca. Stimulant, interferes with dopamine.

Withdrawal symptoms: anxiety, nausea, hallucination on stopping addictive drug.

Treatment: Counselling, rehabilitation. Prevention through education.

Revision Notes

INNATE: skin, mucus, lysozyme, phagocytes (present at birth, non-specific)
ACQUIRED: B-cells (humoral/antibodies) + T-cells (cell-mediated)
ACTIVE: own antibodies (vaccination)
PASSIVE: ready-made antibodies (antiserum, mother→baby)

PRIMARY LYMPHOID: Thymus(T-cells), Bone marrow(B-cells)
SECONDARY: Spleen, Lymph nodes, Tonsils, MALT

DISEASES:
Typhoid: Salmonella typhi (Widal test)
AIDS: HIV (retrovirus, attacks T-helper CD4⁺ cells)
Malaria: Plasmodium (protozoan), Anopheles mosquito
P.falciparum: most dangerous malaria
Dengue: Aedes mosquito, low platelets

VACCINES:
Smallpox: cowpox (Jenner) — first vaccine
BCG: TB | OPV/IPV: Polio | Toxoid: Tetanus
Hep B: recombinant

CANCER: benign(localised) vs malignant(metastasis)
Proto-oncogene → oncogene | p53: tumour suppressor

DRUGS:
Opioids: morphine, heroin (Papaver somniferum)
Cannabinoids: THC (Cannabis sativa)
Cocaine: Erythroxylum coca