Human Health and Disease

2.1 Core concepts

• Health is a state of complete physical, mental and social well-being; it depends on (i) genetic disorders, (ii) infections, and (iii) lifestyle including food, water, rest and exercise (NCERT §7 intro, p. 129–130).
• Diseases are grouped into infectious (easily transmitted person-to-person) and non-infectious; AIDS is a fatal infectious disease and cancer is the major non-infectious killer (NCERT §7 intro, p. 130).
• Typhoid is caused by Salmonella typhi, enters via contaminated food/water, gives sustained 39–40°C fever, weakness, stomach pain, constipation, headache; confirmed by Widal test. Mary Mallon ("Typhoid Mary") was a famous carrier (NCERT §7.1, p. 130–131).
• Pneumonia is caused by Streptococcus pneumoniae and Haemophilus influenzae; alveoli fill with fluid; symptoms include fever, chills, cough, headache and gray/bluish lips & nails in severe cases; spreads through droplets or shared utensils (NCERT §7.1, p. 131).
• Common cold is caused by Rhino viruses, infecting the nose and respiratory passage but not the lungs; symptoms last 3–7 days (NCERT §7.1, p. 131).
• Malaria is caused by Plasmodium (P. vivax, P. malaria, P. falciparum); malignant malaria by P. falciparum is the most serious. Sporozoites enter via female Anopheles bite, multiply in liver, then attack RBCs; rupture releases the toxin haemozoin causing chill and fever every 3–4 days. Malarial parasite needs two hosts — human and mosquito (NCERT §7.1, p. 131, Fig. 7.1).
• Amoebiasis (amoebic dysentery) is caused by Entamoeba histolytica in the large intestine; houseflies act as mechanical carriers; symptoms include constipation, abdominal pain, stools with mucous and blood clots (NCERT §7.1, p. 132–133).
• Ascariasis is caused by Ascaris (roundworm); symptoms include internal bleeding, muscular pain, fever, anemia and intestinal blockage; acquired through contaminated water/vegetables/fruits (NCERT §7.1, p. 133).
• Filariasis (elephantiasis) is caused by Wuchereria (W. bancrofti and W. malayi); chronic inflammation of lymphatic vessels of the lower limbs; transmitted by female mosquito vectors (NCERT §7.1, p. 133, Fig. 7.2).
• Ringworms are caused by fungi of genera Microsporum, Trichophyton and Epidermophyton; produce dry scaly itchy lesions; thrive in skin folds; acquired from soil, towels, clothes, combs (NCERT §7.1, p. 133, Fig. 7.3).
• For vector-borne diseases (malaria, filariasis) control of vectors is paramount; recent Aedes mosquito outbreaks have caused dengue and chikungunya in India (NCERT §7.1, p. 134).
• Innate immunity is non-specific, present at birth, with four barriers — physical (skin, mucus), physiological (acid in stomach, saliva, tears), cellular (neutrophils, monocytes, NK cells, macrophages) and cytokine (interferons from virus-infected cells) (NCERT §7.2.1, p. 134–135).
• Acquired immunity is pathogen-specific and has memory: primary response is low-intensity on first exposure, secondary/anamnestic response is highly intensified (NCERT §7.2.2, p. 135).
• B-lymphocytes produce antibodies; T-lymphocytes help B-cells and also mediate cell-mediated immunity (CMI). Each antibody is H2L2 — two heavy + two light peptide chains. Types: IgA, IgD, IgE, IgG, IgM. Antibody-mediated response = humoral immune response (NCERT §7.2.2, p. 135–136, Fig. 7.4).
• CMI is responsible for graft rejection — the body distinguishes 'self' from 'non-self' (NCERT §7.2.2, p. 136).
• Active immunity = host produces antibodies after exposure to antigen (slow); passive immunity = ready-made antibodies given. Examples: colostrum (IgA-rich, mother's first milk) and antibodies via placenta during pregnancy (NCERT §7.2.3, p. 136).
• Vaccination uses inactivated/weakened pathogen or antigenic proteins to create memory B and T-cells. Passive immunisation uses preformed antibodies (tetanus antitoxin, snake antivenom). Recombinant DNA technology produces vaccines like the hepatitis B vaccine from yeast (NCERT §7.2.4, p. 136).
• Allergy = exaggerated immune response to environmental antigens (allergens like dust mites, pollens, animal dander). Antibodies are IgE; chemicals released are histamine and serotonin from mast cells; treated with anti-histamine, adrenalin, steroids (NCERT §7.2.5, p. 137).
• Auto-immune disease — body attacks its own cells; example rheumatoid arthritis (NCERT §7.2.6, p. 137).
• Primary lymphoid organs: bone marrow and thymus (lymphocyte maturation). Secondary lymphoid organs: spleen, lymph nodes, tonsils, Peyer's patches, appendix. MALT = mucosa-associated lymphoid tissue, ~50% of body's lymphoid tissue (NCERT §7.2.7, p. 137–138, Fig. 7.5).
• AIDS (Acquired Immuno Deficiency Syndrome) was first reported in 1981; caused by HIV, a retrovirus with an envelope enclosing an RNA genome. Transmission: sexual contact, contaminated blood, shared infected needles, infected mother to child via placenta. Time lag between infection and symptoms = 5–10 years (NCERT §7.3, p. 138–139, Fig. 7.6).
• HIV enters macrophages; reverse transcriptase converts viral RNA into viral DNA, which integrates into host DNA. HIV then attacks helper T-lymphocytes (TH), progressively decreasing their number; patient becomes immuno-deficient. Diagnostic test = ELISA (enzyme linked immuno-sorbent assay). Treatment with anti-retroviral drugs only prolongs life (NCERT §7.3, p. 140).
• Prevention efforts include NACO (National AIDS Control Organisation), safe blood, disposable needles, condoms, safe sex (NCERT §7.3, p. 140).
• Cancer: cancer cells have lost contact inhibition; masses are called tumors. Benign tumors stay confined; malignant tumors (neoplastic cells) divide rapidly, invade nearby tissues, starve normal cells and undergo metastasis — spread via blood to start tumors elsewhere (NCERT §7.4, p. 141).
• Carcinogens cause cancer — ionising radiations (X-rays, gamma rays), non-ionising (UV) cause DNA damage; chemical carcinogens in tobacco smoke cause lung cancer. Oncogenic viruses carry viral oncogenes; normal cells contain cellular oncogenes (c-onc) / proto-oncogenes which on activation cause oncogenic transformation (NCERT §7.4, p. 141).
• Cancer detection uses biopsy and histopathology, blood/bone marrow tests for leukemias, radiography, CT, MRI, antibodies against cancer-specific antigens, and molecular biology for inherited susceptibility (NCERT §7.4, p. 141–142).
• Cancer treatment: surgery, radiotherapy, chemotherapy, immunotherapy. Biological response modifiers like α-interferon activate the immune system to destroy the tumor (NCERT §7.4, p. 142).
• Opioids bind to opioid receptors in CNS and gastrointestinal tract. Heroin (smack) = diacetylmorphine, made by acetylation of morphine from latex of opium poppy Papaver somniferum; taken by snorting/injection; depressant (NCERT §7.5, p. 142–143, Fig. 7.7–7.8).
• Cannabinoids interact with cannabinoid receptors mainly in the brain; obtained from inflorescences of Cannabis sativa; flower tops, leaves and resin produce marijuana, hashish, charas and ganja; affect cardiovascular system; taken by inhalation/oral ingestion (NCERT §7.5, p. 143, Fig. 7.9–7.10).
• Cocaine (coke/crack) is a coca alkaloid from Erythroxylum coca (South America); interferes with neurotransmitter dopamine transport; potent CNS stimulant; excessive doses cause hallucinations. Other hallucinogenic plants: Atropa belladonna and Datura (NCERT §7.5, p. 143, Fig. 7.11).
• Tobacco contains nicotine, an alkaloid; stimulates adrenal gland to release adrenaline and nor-adrenaline (raising BP, heart rate); linked to lung/bladder/throat cancer, bronchitis, emphysema, coronary heart disease; smoking raises CO in blood, reducing haem-bound oxygen (NCERT §7.5, p. 144).
• Addiction is psychological attachment to drug-induced euphoria; dependence leads to a withdrawal syndrome (anxiety, shakiness, nausea, sweating) on stopping (NCERT §7.5.2, p. 145).
• Intravenous drug abuse spreads AIDS and Hepatitis B through shared needles; chronic alcohol use causes liver cirrhosis; misuse of anabolic steroids by sportspersons causes masculinisation in females and acne, mood swings, testicular shrinkage in males (NCERT §7.5.3, p. 146).
• Prevention measures: avoid undue peer pressure, education and counselling, seeking help from parents/peers, looking for danger signs, professional/medical help via psychologists and de-addiction programmes (NCERT §7.5.4, p. 146–147).

2.2 Definitions to memorise

2.3 Diagrams / processes to remember

• **Figure 7.1 — Life cycle of *Plasmodium*** (p. 132): sporozoites injected by Anopheles → liver cell asexual reproduction → RBC infection and rupture → gametocytes taken up by female mosquito → fertilisation in mosquito gut → sporozoites migrate to salivary glands.
• Figure 7.2 — Elephantiasis (p. 133): inflammation of lower limb due to Wuchereria in lymphatic vessels.
• Figure 7.3 — Ringworm lesion on skin (p. 133).
• Figure 7.4 — Antibody structure (p. 135): Y-shaped, two antigen-binding sites at N-terminus, two light chains and two heavy chains; represented as H2L2.
• Figure 7.5 — Lymph nodes / lymphoid organs in human body (p. 138).
• Figure 7.6 — Replication of retrovirus (HIV) (p. 139): viral RNA core → enters cell → viral DNA produced by reverse transcriptase → integrates into host genome → new viral RNA → new viruses released.
• Figure 7.7 — Chemical structure of morphine (p. 142).
• **Figure 7.8 — Opium poppy *Papaver somniferum*** (p. 142).
• Figure 7.9 — Cannabinoid skeletal structure and **Figure 7.10 — Leaves of *Cannabis sativa*** (p. 143).
• Figure 7.11 — Datura flowering branch (p. 143).

2.4 Common confusions / NTA trap points

• Aedes is the vector for dengue and chikungunya, NOT for amoebiasis (amoebiasis uses houseflies as mechanical carriers) and NOT for malaria (which uses **female *Anopheles***).
• Common cold infects the nose and respiratory passage but NOT the lungs — students often wrongly mark "lungs".
• Antibody is H2L2 (two heavy + two light chains), not H4 or L4.
• The mother's gift of colostrum (IgA-rich) is passive immunity, not active.
• Reverse transcriptase is found in HIV (a retrovirus) and makes DNA from RNA, not the other way.
• Plasmodium falciparum causes malignant malaria — most fatal species; do not confuse with P. vivax (most common, less severe).
• Primary lymphoid organs = bone marrow + thymus; secondary = spleen, lymph nodes, tonsils, Peyer's patches, appendix. Students mix the two.
• Hepatitis B vaccine is made from yeast (recombinant DNA), not from inactivated virus in the NCERT context.
• Heroin (smack) = diacetylmorphine made from morphine of Papaver somniferum; cocaine is from Erythroxylum coca. These often get swapped.