Export chapter — Human Health and Disease

Human Health and Disease — Long Notes

Health as defined by the World Health Organization is a state of complete physical, mental, and social well-being, not merely the absence of disease or infirmity. Diseases can be infectious (caused by pathogens) or non-infectious (metabolic, degenerative, cancer, mental disorders).

1. Common Diseases in Humans

1.1 Bacterial Diseases

Typhoid — Salmonella typhi.
Transmitted through contaminated food/water.
Symptoms: high fever, weakness, stomach pain, constipation, headache.
Diagnosis: Widal test (detects antibodies).
Pneumonia — Streptococcus pneumoniae, Haemophilus influenzae.
Fluid fills alveoli → breathing difficulty.
Spreads by droplets from infected persons.

1.2 Viral Diseases

Common cold — Rhinoviruses. Nasal congestion, sneezing, cough. Spreads by droplets.
Dengue — dengue virus, spread by Aedes mosquito bite. Fever, joint pain, rash; severe cases: haemorrhagic fever.
Chikungunya — similar transmission and symptoms.

1.3 Protozoan Diseases

Malaria — genus Plasmodium; species: P. vivax, P. malariae, P. falciparum (most dangerous — cerebral malaria).
Vector: female Anopheles mosquito.
Life cycle:

Infected mosquito bites → injects sporozoites with saliva.
Sporozoites reach liver → multiply → reach RBCs → multiply.
RBCs rupture → release parasites and haemozoin — a toxin that causes chill and high fever (every 3–4 days).
In the mosquito, sexual reproduction → new sporozoites.

Amoebiasis (amoebic dysentery) — Entamoeba histolytica. Constipation, abdominal pain, stools with mucus and blood. Vector: houseflies.

1.4 Fungal Diseases

Ringworm — Microsporum, Trichophyton, Epidermophyton.
Dry, scaly lesions on skin, nails, scalp. Spread by soil, towels, clothes.

1.5 Helminth Diseases

Ascariasis — Ascaris (roundworm). Internal bleeding, muscle pain, fever, blocked intestines. Spread via contaminated water/vegetables.
Elephantiasis (filariasis) — Wuchereria bancrofti and W. malayi, transmitted by Culex mosquito. Adult worms live in lymph vessels → gross swelling of lower limbs, genitals.

1.6 Prevention (general rules)

Personal and public hygiene.
Safe drinking water and food.
Vector control (destroy mosquito breeding sites, use nets, insecticides).
Vaccinations against communicable diseases.
Timely diagnosis and treatment.

2. The Immune System

2.1 Innate (Non-specific) Immunity

Present from birth; consists of 4 barriers:

Physical — skin (waterproof, keratinised), mucous membranes of respiratory, digestive, and urogenital tracts.
Physiological — HCl in stomach kills most microbes; tears (lysozyme), saliva.
Cellular — phagocytes: neutrophils, monocytes/macrophages, NK cells.
Cytokine — interferons secreted by virus-infected cells warn neighbours.

2.2 Acquired (Specific) Immunity

Develops with exposure. Two responses, both mediated by lymphocytes:

B cells → antibodies → humoral (antibody-mediated) immunity.
T cells → cell-mediated immunity:
Helper T cells activate B and other T cells.
Cytotoxic T cells destroy infected/cancer cells.
Regulatory T cells (suppressors) prevent overreaction.

2.3 Active vs Passive

Active immunity — body makes its own antibodies after infection or vaccination. Slow but long-lasting.
Passive immunity — ready-made antibodies given (e.g. colostrum contains IgA, anti-tetanus serum). Immediate but temporary.

2.4 Antibody Structure

Y-shaped protein with 4 polypeptide chains — 2 heavy (H) + 2 light (L) — often written as H₂L₂.
Each arm has a variable region that binds a specific antigen; the stem is constant.
5 classes — IgA, IgD, IgE, IgG, IgM.

Class	Notable role
IgG	Most abundant; crosses placenta; long-term memory
IgA	Mucosal surfaces; colostrum
IgM	First to appear in infection
IgE	Allergic reactions (binds mast cells)
IgD	B-cell receptor

3. Vaccination and Immunisation

Vaccines expose the body to attenuated, killed, or antigenic parts of a pathogen. The immune system responds by making antibodies and memory cells, so a later real infection is dealt with quickly.

Recombinant DNA vaccines — e.g. Hepatitis-B vaccine produced by expressing HBsAg in yeast.
Passive immunisation — pre-formed antibodies (anti-snake venom, anti-tetanus serum) for immediate protection.

4. Allergies and Autoimmunity

Allergy — exaggerated response to environmental allergens (dust, pollen, mite, animal dander).
Mediated by IgE + mast cells → release histamine, serotonin → sneezing, wheezing, watery eyes.
Treatment: anti-histamines, steroids, adrenaline (for shock).
Autoimmunity — immune system attacks the body's own tissues.
Example: rheumatoid arthritis (joint destruction).

5. Immune System in Humans — Organs

Primary lymphoid organs (where lymphocytes mature): bone marrow, thymus.
Secondary lymphoid organs (where mature lymphocytes fight infection): spleen, lymph nodes, tonsils, MALT (mucosa-associated lymphoid tissue), Peyer's patches.

6. AIDS

Acquired Immuno Deficiency Syndrome, caused by the Human Immunodeficiency Virus (HIV) — a retrovirus containing RNA and reverse transcriptase.

Transmission

Sexual contact with infected person.
Sharing needles/syringes with infected drug users.
Transfusion of infected blood.
Infected mother to foetus (via placenta) or infant (via breast milk).

NOT spread by: shaking hands, hugging, shared food, mosquito bites, using same toilet.

Progression

HIV enters macrophage → reverse transcriptase makes DNA from viral RNA → integrated into host genome.
Macrophage becomes a HIV factory → virus infects helper T cells (CD4) → they die.
Immune system weakens → opportunistic infections (TB, pneumocystis, cancers).
From infection to full AIDS may take months to 10+ years.

Diagnosis

ELISA (Enzyme-Linked Immunosorbent Assay) — detects HIV antibodies.

Treatment & Prevention

Anti-retroviral therapy (ART) — combination of drugs that slow the virus, not curative.
Prevention: safe sex, screened blood, disposable needles, HIV testing, awareness. NACO (National AIDS Control Organisation) leads India's response.

7. Cancer

Uncontrolled cell division.

7.1 Normal vs Cancer Cell

Normal cells stop dividing on contact with neighbours (contact inhibition) and adhere in the correct places. Cancer cells lose these controls and proliferate unregulated.

7.2 Types of Tumours

Benign — remain confined; do not spread.
Malignant — invade surrounding tissues, may spread via metastasis (secondary tumours).

7.3 Causes of Cancer

Physical carcinogens — X-rays, gamma rays, UV.
Chemical carcinogens — cigarette smoke (nicotine, tar, PAHs), asbestos.
Biological (oncogenic viruses) — HPV (cervical cancer), HBV (liver cancer), EBV (Burkitt lymphoma).
Oncogenes — mutated forms of normal cellular genes (proto-oncogenes) that push cells to divide.

7.4 Detection

Biopsy and histopathology.
Radiography, CT scans, MRI.
Antibody tests for cancer-specific antigens.
Molecular biology techniques.

7.5 Treatment

Surgery — remove localised tumour.
Radiotherapy — kills cancer cells with ionising radiation.
Chemotherapy — drugs kill dividing cells (but also affect other rapidly dividing tissues).
Immunotherapy — biological response modifiers, e.g. α-interferons, boost the immune attack.

8. Drugs and Alcohol Abuse

Adolescents are often exposed to drugs and alcohol via curiosity, peer pressure, or coping with stress.

8.1 Common Drugs

Opioids — heroin, smack. From opium poppy Papaver somniferum. Suppress brain function (CNS depressants). Highly addictive.
Cannabinoids — marijuana, hashish, ganja, charas. From Cannabis sativa. Affect the cardiovascular system.
Cocaine (coke, crack) — from Erythroxylum coca. Interferes with dopamine transport → euphoria, then hallucinations.
Barbiturates, amphetamines, benzodiazepines — normally prescribed but abused.
Tobacco — nicotine → releases adrenaline & noradrenaline → increased BP and heart rate; smoking causes cancers of lung, oral cavity, bladder.
Alcohol — CNS depressant; long-term abuse → cirrhosis of liver.

8.2 Adverse Effects

Withdrawal syndrome (anxiety, tremors, nausea, sweating).
Reckless behaviour, accidents.
Damage to liver, brain, nervous system.
Loss of studies/job, family conflict, financial ruin.

8.3 Prevention and Control

Avoid peer pressure and identify the actual problem behind the urge.
Seek help from parents, teachers, counsellors, professional rehabilitation centres.
Community education, family bonding, healthy hobbies.

Key take-aways

Diseases can be infectious (many pathogens with typical transmission routes) or non-infectious (cancer, autoimmune, drug-abuse related).
Immunity works in layers: innate + acquired, humoral + cell-mediated, active + passive.
Vaccination is the most powerful public-health tool; classic recombinant example is the Hepatitis-B vaccine.
AIDS is caused by HIV, spreads through specific fluids only; detected by ELISA; managed but not cured by ART.
Cancer results from loss of normal cell-cycle controls; multi-modal treatment (surgery + radiation + chemo + immunotherapy) improves survival.
Drug and alcohol abuse have profound biological and social costs; awareness and support are essential.