Learning Objectives
- Understand common human diseases and their causes
- Learn about the immune system and types of immunity
- Study AIDS, cancer, and drug abuse
- Understand vaccination and immunization
Key Concepts
Common Diseases
Bacterial: Typhoid (Salmonella typhi — Widal test for diagnosis), Pneumonia (Streptococcus pneumoniae, Haemophilus influenzae). Viral: Common cold (Rhinovirus), AIDS (HIV). Protozoan: Malaria (Plasmodium — P. vivax, P. falciparum most dangerous; vector: female Anopheles mosquito; infects liver cells then RBCs; recurrent fever pattern), Amoebiasis (Entamoeba histolytica — bloody diarrhoea). Helminthic: Ascariasis (Ascaris lumbricoides), Filariasis (Wuchereria bancrofti — elephantiasis; vector: Culex mosquito). Fungal: Ringworm (Microsporum, Trichophyton, Epidermophyton).
Immunity
Innate immunity: Non-specific, present from birth. Barriers: Physical (skin, mucus), Physiological (HCl in stomach, tears — lysozyme), Cellular (WBCs — neutrophils, monocytes, macrophages — phagocytosis), Cytokine barrier (interferons — protect uninfected cells from viral infection).
Adaptive/Acquired immunity: Specific, develops after exposure. (1) Humoral immunity: B-lymphocytes produce antibodies (immunoglobulins — IgG, IgA, IgM, IgE, IgD). Antibody structure: 2 heavy chains + 2 light chains, Y-shaped, antigen-binding sites at tips. (2) Cell-mediated immunity: T-lymphocytes (cytotoxic T cells kill infected cells). Primary immune response: Low intensity, slow. Secondary (anamnestic) response: Fast, intense (due to memory cells).
Active immunity: Body produces antibodies (natural — infection; artificial — vaccination). Passive immunity: Ready-made antibodies transferred (natural — mother to foetus via placenta/colostrum; artificial — antiserum injection, e.g., anti-tetanus serum).
Vaccination: Weakened/killed pathogens stimulate immune response. Examples: Polio vaccine (Salk — killed; Sabin — oral, live attenuated), BCG (tuberculosis), DPT (diphtheria, pertussis, tetanus).
AIDS (Acquired Immuno Deficiency Syndrome)
Caused by HIV (Human Immunodeficiency Virus) — a retrovirus (RNA genome + reverse transcriptase). Attacks helper T cells (CD4+). Transmission: sexual contact, contaminated blood/needles, mother to child. Diagnosis: ELISA (screening), Western Blot (confirmatory). No cure; antiretroviral therapy (ART) slows progression. HIV lifecycle: RNA → DNA (reverse transcriptase) → integrates into host DNA → produces new virions.
Cancer
Uncontrolled cell division due to mutation in proto-oncogenes (become oncogenes) or inactivation of tumour suppressor genes (e.g., p53, Rb). Benign tumour: Localized, non-spreading. Malignant tumour: Invasive, spreads — metastasis (cells travel through blood/lymph). Causes: Physical (radiation, UV), Chemical (carcinogens — tobacco, nickel), Biological (oncogenic viruses). Detection: Biopsy, MRI, CT scan, molecular markers. Treatment: Surgery, radiation, chemotherapy, immunotherapy.
Drugs and Alcohol Abuse
Opioids: Morphine, heroin (smack) — from Papaver somniferum (opium poppy); bind to opioid receptors. Cannabinoids: Marijuana, hashish, ganja — from Cannabis sativa; affect cardiovascular system. Coca alkaloid: Cocaine — from Erythroxylum coca; stimulant. Effects: Addiction, withdrawal symptoms, damage to liver (cirrhosis), nervous system, cardiovascular system, immune suppression.
Summary
Human diseases are caused by bacteria, viruses, protozoans, helminths, and fungi. The immune system provides innate and adaptive immunity. AIDS is caused by HIV attacking helper T cells. Cancer results from uncontrolled cell division due to oncogene activation or tumour suppressor inactivation. Drug and alcohol abuse has severe physiological and psychological effects.
Important Terms
- Antibody: Immunoglobulin protein produced by B cells against specific antigen
- Antigen: Foreign substance that triggers immune response
- Metastasis: Spread of cancer cells to distant body parts
- Retrovirus: RNA virus with reverse transcriptase (e.g., HIV)
- Vaccination: Introduction of weakened/killed pathogen to stimulate immunity
- Interferon: Protein released by virus-infected cells to protect neighbouring cells
- Oncogene: Mutated proto-oncogene causing uncontrolled cell division
- ELISA: Enzyme-Linked Immunosorbent Assay for disease detection
Quick Revision
- Malaria: Plasmodium, female Anopheles mosquito; Filariasis: Wuchereria, Culex
- Typhoid: Salmonella typhi, Widal test diagnosis
- Innate immunity: non-specific, from birth; Adaptive: specific, after exposure
- B cells → antibodies (humoral); T cells → cell-mediated immunity
- HIV: retrovirus, attacks CD4+ T cells; ELISA for screening
- Cancer: oncogenes (activated) + tumour suppressors (inactivated); metastasis = spread
- Active immunity: body makes antibodies; Passive: ready-made antibodies given
- Colostrum: IgA antibodies — passive natural immunity to newborn