Human Health and Disease

Key Concepts

Definition of Health

Health is a state of complete physical, mental, and social well-being, and not merely the absence of disease or infirmity. It is maintained by a balanced diet, personal hygiene, and regular exercise (including Yoga).

Common Diseases in Humans

Pathogens (bacteria, viruses, fungi, protozoans, etc.) cause diseases by entering and multiplying within the host.

• Bacterial Diseases:
  • Typhoid: Caused by Salmonella typhi. Confirmed by Widal test. Symptoms: sustained high fever, weakness, intestinal perforation.
  • Pneumonia: Caused by Streptococcus pneumoniae. Affects lungs (alveoli).
• Viral Diseases:
  • Common Cold: Caused by Rhino viruses. Affects nose and respiratory passage but not lungs.
• Protozoan Diseases:
  • Malaria: Caused by Plasmodium (P. vivax, P. malaria, P. falciparum). Transmitted by female Anopheles mosquito (vector). Parasite multiplies in liver and attacks RBCs, releasing haemozoin (causes chills and fever).
  • Amoebiasis: Caused by Entamoeba histolytica.
• Helminthic Diseases:
  • Ascariasis: Caused by Ascaris (roundworm).
  • Filariasis (Elephantiasis): Caused by Wuchereria (W. bancrofti and W. malayi). Causes chronic inflammation of lymphatic vessels.
• Fungal Diseases:
  • Ringworm: Caused by Microsporum, Trichophyton, Epidermophyton. Dry, scaly lesions on skin.

Immunity

The ability of the host to fight disease-causing organisms.

• Innate Immunity: Non-specific; present at birth. Barriers: Physical (skin), Physiological (acid in stomach), Cellular (WBCs/macrophages), and Cytokine (interferons).
• Acquired Immunity: Pathogen-specific; characterized by memory.
  • Primary Response: Low intensity on first encounter.
  • Secondary Response: Highly intensified on subsequent encounter.
  • Lymphocytes: B-cells (produce antibodies) and T-cells (help B-cells and mediate CMI).
• Antibody Structure: H2L2 (two heavy and two light chains). Types: IgA, IgM, IgE, IgG.
• Active vs Passive Immunity:
  • Active: Produced in host body (slow, long-lasting).
  • Passive: Preformed antibodies injected (e.g., Colostrum, anti-venom).

Vaccination and Immunisation

Based on the property of 'memory'. Recombinant DNA technology allows for large-scale vaccine production (e.g., Hepatitis B from yeast).

Auto-immunity and Allergies

• Allergy: Exaggerated response to environmental antigens (allergens). Mediated by IgE and chemicals like histamine/serotonin.
• Auto-immunity: Body attacks self-cells (e.g., Rheumatoid arthritis).

AIDS (Acquired Immuno Deficiency Syndrome)

• Caused by HIV (Retrovirus with RNA genome).
• Transmission: Sexual contact, contaminated blood, shared needles, infected mother to child.
• Mechanism: HIV attacks Helper T-lymphocytes (TH), leading to a progressive decrease in their number.
• Diagnosis: ELISA.

Cancer

Breakdown of regulatory mechanisms; loss of contact inhibition.

• Tumors: Benign (localized) and Malignant (proliferating, invasive).
• Metastasis: Feared property where cancer cells spread to distant sites via blood.
• Carcinogens: Physical (UV, X-rays), Chemical (tobacco smoke), and Biological (oncogenic viruses).

Drugs and Alcohol Abuse

• Opioids: e.g., Heroin (smack). Extracted from Poppy plant Papaver somniferum. Depressant.
• Cannabinoids: e.g., Marijuana, Ganja. From Cannabis sativa. Affects cardiovascular system.
• Coca Alkaloids: e.g., Cocaine. From Erythroxylum coca. Stimulant, causes euphoria/hallucinations.
• Tobacco: Contains nicotine; stimulates adrenaline, increases BP.
• Adolescence: A bridge linking childhood and adulthood; highly vulnerable phase for addiction.
• Addiction & Dependence: Psychological attachment to effects and 'withdrawal syndrome' upon discontinuation.