Class 12 Notes

Class 12 Biology Notes Chapter 8 (Human health and disease) – Biology Book

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Philoid

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Biology
Alright, let's focus on Chapter 8, 'Human Health and Disease'. This is a crucial chapter for understanding basic biology and is frequently tested in various government exams. Pay close attention to the details, especially causative agents, vectors, types of immunity, and specific diseases like AIDS and Cancer.

Chapter 8: Human Health and Disease - Detailed Notes

1. Health:

  • Definition (WHO): Health is a state of complete physical, mental, and social well-being and not merely the absence of disease or infirmity.
  • Factors Affecting Health:
    • Genetic Disorders: Inherited defects.
    • Infections: Caused by pathogens.
    • Lifestyle: Diet, exercise, habits (smoking, alcohol), stress.
  • Good Health Maintenance: Balanced diet, personal hygiene, regular exercise, awareness about diseases, proper waste disposal, control of vectors, vaccination.

2. Common Diseases in Humans:

  • Pathogens: Disease-causing organisms (Bacteria, Viruses, Fungi, Protozoans, Helminths).

  • Modes of Transmission: Direct contact, indirect contact (fomites), droplets, vectors (insects, animals), contaminated food/water.

    • A. Bacterial Diseases:

      • Typhoid:
        • Pathogen: Salmonella typhi (bacterium).
        • Transmission: Contaminated food and water.
        • Site of Infection: Small intestine, migrates to other organs via blood.
        • Symptoms: Sustained high fever (39°-40°C), weakness, stomach pain, constipation, headache, loss of appetite. Intestinal perforation and death may occur in severe cases.
        • Diagnosis: Widal Test.
        • Carrier Example: Typhoid Mary (Mary Mallon).
      • Pneumonia:
        • Pathogen: Streptococcus pneumoniae, Haemophilus influenzae (bacteria).
        • Transmission: Inhaling droplets/aerosols from infected person, sharing utensils.
        • Site of Infection: Alveoli of the lungs; alveoli get filled with fluid.
        • Symptoms: Fever, chills, cough, headache. In severe cases, lips and fingernails may turn gray to bluish.
      • Other Bacterial Diseases: Dysentery, Plague, Diphtheria.

    • B. Viral Diseases:

      • Common Cold:
        • Pathogen: Rhinoviruses (group of viruses).
        • Transmission: Inhaling droplets from cough/sneeze, contaminated objects (pens, books, etc.).
        • Site of Infection: Nose and respiratory passage (NOT lungs).
        • Symptoms: Nasal congestion and discharge, sore throat, hoarseness, cough, headache, tiredness (usually lasts 3-7 days).
      • Other Viral Diseases: Influenza, Polio, Dengue, Chikungunya, AIDS (discussed later).

    • C. Protozoan Diseases:

      • Malaria:
        • Pathogen: Plasmodium species (P. vivax, P. malariae, P. falciparum). P. falciparum causes malignant malaria, which is most serious and can be fatal.
        • Vector: Female Anopheles mosquito.
        • Life Cycle:
          1. Sporozoites (infectious form) injected by mosquito bite.
          2. Reach liver cells, multiply (asexual reproduction).
          3. Burst liver cells, release into blood.
          4. Invade Red Blood Cells (RBCs), multiply asexually (form Merozoites).
          5. Burst RBCs, releasing Haemozoin (toxic substance causing chills and high fever recurring every 3-4 days).
          6. Released parasites infect new RBCs.
          7. Some develop into Gametocytes (male and female) in RBCs.
          8. Mosquito bites infected person, ingests gametocytes with blood.
          9. Fertilization and development occur in mosquito's gut.
          10. Sporozoites formed, migrate to mosquito's salivary glands, ready to infect another human.
        • Symptoms: High fever recurring at intervals, chills.
        • Control: Eradicate vectors (mosquitoes) and avoid bites.
      • Amoebiasis (Amoebic Dysentery):
        • Pathogen: Entamoeba histolytica (protozoan).
        • Transmission: Faeco-oral route (contaminated food/water). Houseflies act as mechanical carriers.
        • Site of Infection: Large intestine.
        • Symptoms: Constipation, abdominal pain and cramps, stools with excess mucus and blood clots.

    • D. Fungal Diseases:

      • Ringworm:
        • Pathogen: Fungi of genera Microsporum, Trichophyton, Epidermophyton.
        • Transmission: From soil, or by using towels, clothes, comb of infected individuals.
        • Symptoms: Appearance of dry, scaly lesions on skin, nails, scalp. Intense itching. Heat and moisture help fungi grow (groin, between toes).

    • E. Helminthic Diseases:

      • Ascariasis:
        • Pathogen: Ascaris lumbricoides (intestinal roundworm).
        • Transmission: Faeco-oral route (contaminated water, vegetables, fruits). Eggs excreted with faeces contaminate soil.
        • Symptoms: Internal bleeding, muscular pain, fever, anaemia, blockage of the intestinal passage.
      • Filariasis (Elephantiasis):
        • Pathogen: Wuchereria bancrofti, Wuchereria malayi (filarial worms).
        • Vector: Female Culex mosquito.
        • Symptoms: Chronic inflammation of organs where they live (usually lymphatic vessels of lower limbs, causing gross deformities - elephantiasis). Genital organs can also be affected.

  • Prevention and Control of Infectious Diseases:

    • Personal Hygiene: Keep body clean, consume clean food/water.
    • Public Hygiene: Proper waste disposal, periodic cleaning of water reservoirs, standard practices in handling food.
    • Vector Control: Eradicating vectors (e.g., mosquitoes - draining stagnant water, insecticides, introducing larvivorous fish like Gambusia, using nets/repellents).
    • Vaccination and Immunization.

3. Immunity:

  • Definition: Overall ability of the host to fight disease-causing organisms.

  • Types:

    • A. Innate Immunity (Non-specific): Present at birth. Consists of four types of barriers:
      • Physical Barriers: Skin (prevents entry), Mucus coating (lining respiratory, gastrointestinal, urogenital tracts traps microbes).
      • Physiological Barriers: Acid in stomach (HCl), Saliva in mouth, Tears from eyes (contain lysozyme).
      • Cellular Barriers: Certain leukocytes (WBCs) like Polymorpho-Nuclear Leukocytes (PMNL-neutrophils), Monocytes, Natural Killer (NK) cells (type of lymphocyte), Macrophages in tissues phagocytose microbes.
      • Cytokine Barriers: Virus-infected cells secrete proteins called Interferons which protect non-infected cells from further viral infection.
    • B. Acquired Immunity (Specific): Pathogen-specific, characterized by Memory. When the body encounters a pathogen for the first time, it produces a Primary Response (low intensity). Subsequent encounter with the same pathogen elicits a highly intensified Secondary (Anamnestic) Response due to memory.
      • Mediated by Lymphocytes (B-lymphocytes and T-lymphocytes).
      • Humoral Immune Response (Antibody-Mediated Immunity - AMI): Mediated by B-lymphocytes. They produce proteins called Antibodies in response to pathogens in blood/body fluids.
        • Antibody Structure: 'Y' shaped molecule. Each molecule has 4 peptide chains: 2 small Light (L) chains and 2 longer Heavy (H) chains (H2L2). Different types exist (IgA, IgM, IgE, IgG). Contains Antigen-binding sites.
      • Cell-Mediated Immune Response (CMI): Mediated by T-lymphocytes.
        • T-cells themselves don't secrete antibodies but help B-cells produce them.
        • Directly attack infected cells, cancer cells.
        • Responsible for Graft Rejection (differentiating 'self' and 'non-self'). Immunosuppressants are needed for transplant patients.
      • Types of Acquired Immunity:
        • Active Immunity: Host produces antibodies in response to antigens (infection or vaccination). Slow but long-lasting.
          • Natural Active: Develops during natural infection.
          • Artificial Active: Develops after vaccination (introduction of weakened/inactivated pathogens or antigenic proteins).
        • Passive Immunity: Ready-made antibodies are given directly. Provides immediate relief but is not long-lasting.
          • Natural Passive: Antibodies from mother to foetus via placenta (IgG) or through colostrum (first milk, rich in IgA) to infant.
          • Artificial Passive: Injection of pre-formed antibodies or antitoxin (e.g., anti-tetanus serum, anti-snake venom).

  • Vaccination and Immunization:

    • Based on the principle of 'memory' of the immune system.
    • A preparation of antigenic proteins of pathogen or inactivated/weakened pathogen (vaccine) is introduced.
    • This triggers antibody production and generates memory B and T-cells.
    • On subsequent actual infection, the memory cells recognize the pathogen quickly and mount a massive secondary response.
    • Modern methods (Recombinant DNA technology) allow large-scale production of antigenic polypeptides (e.g., Hepatitis B vaccine from yeast).

  • Allergies:

    • Exaggerated response of the immune system to certain antigens present in the environment, called Allergens (e.g., pollens, dust mites, animal dander, certain foods).
    • Antibody produced: IgE type.
    • Mechanism: Allergens cause release of chemicals like Histamine and Serotonin from Mast cells.
    • Symptoms: Sneezing, watery eyes, running nose, difficulty breathing.
    • Diagnosis: Exposure to or injection of suspected allergens, reaction studied.
    • Treatment: Antihistamines, adrenaline, steroids.

  • Autoimmunity:

    • Immune system attacks self-cells due to genetic or unknown reasons. Body fails to differentiate self from non-self.
    • Example: Rheumatoid Arthritis.

  • Immune System in the Body:

    • Includes Lymphoid Organs, tissues, cells, and soluble molecules (antibodies).
    • Lymphoid Organs: Where origin, maturation, and proliferation of lymphocytes occur.
      • Primary Lymphoid Organs: Bone Marrow and Thymus. Immature lymphocytes differentiate into antigen-sensitive lymphocytes.
        • Bone Marrow: Main lymphoid organ; all blood cells including lymphocytes are produced here. B-cell maturation occurs here.
        • Thymus: Located near heart, beneath breastbone. Large at birth, reduces with age. T-cell maturation occurs here.
      • Secondary Lymphoid Organs: Spleen, Lymph Nodes, Tonsils, Peyer's Patches (small intestine), Appendix. Provide sites for interaction of lymphocytes with antigens, leading to proliferation and differentiation into effector cells.
        • Spleen: Large bean-shaped organ. Filters blood (traps blood-borne microorganisms). Has lymphocytes and phagocytes. Reservoir of erythrocytes.
        • Lymph Nodes: Small solid structures along lymphatic vessels. Trap microorganisms/antigens entering lymph/tissue fluid. Activate lymphocytes present there.
        • Mucosa-Associated Lymphoid Tissue (MALT): Located within lining of major tracts (respiratory, digestive, urogenital). Constitutes about 50% of lymphoid tissue.

4. AIDS (Acquired Immuno Deficiency Syndrome):

  • Definition: Deficiency of immune system, acquired during lifetime (not congenital). Syndrome = group of symptoms.
  • Causative Agent: Human Immunodeficiency Virus (HIV), a Retrovirus (has RNA genome, enveloped).
  • Transmission:
    • Sexual contact with infected person.
    • Transfusion of contaminated blood/blood products.
    • Sharing infected needles (IV drug abusers).
    • From infected mother to child through placenta.
    • Not spread by: Touch, physical contact, sharing meals. Spreads only through body fluids.
  • Mechanism of Infection:
    1. HIV enters the body.
    2. Virus enters Macrophages (acts as HIV factory).
    3. Viral RNA replicates to form viral DNA using enzyme Reverse Transcriptase.
    4. Viral DNA incorporates into host cell's DNA, directs infected cells to produce virus particles.
    5. HIV enters Helper T-lymphocytes (TH cells), replicates and produces progeny viruses.
    6. Progeny viruses released, attack other helper T-cells.
    7. Progressive decrease in the number of helper T-cells.
    8. Severe immunodeficiency results, person susceptible to opportunistic infections (bacteria like Mycobacterium, viruses, fungi, parasites like Toxoplasma).
  • Time Lag: Between infection and appearance of symptoms, can range from few months to many years (5-10 years).
  • Diagnosis: ELISA (Enzyme-Linked Immunosorbent Assay). Western Blotting is confirmatory.
  • Symptoms: Bouts of fever, diarrhoea, weight loss. Opportunistic infections. Cancers.
  • Treatment: Anti-retroviral drugs are partially effective. They can prolong life but cannot prevent death (no cure yet).
  • Prevention:
    • Education and awareness (NACO - National AIDS Control Organisation, NGOs).
    • Safe sex practices (condoms).
    • Ensuring safe blood transfusions (screening blood).
    • Discouraging drug abuse, using disposable needles.
    • Regular check-ups for HIV in susceptible populations.

5. Cancer:

  • Definition: Uncontrolled cell growth and division. Normal cells show Contact Inhibition (contact with other cells inhibits their uncontrolled growth); cancer cells lose this property.
  • Tumors: Masses of cells resulting from uncontrolled division.
    • Benign Tumors: Remain confined to original location, do not spread, cause little damage generally.
    • Malignant Tumors: Mass of proliferating cells (Neoplastic or tumor cells). Grow rapidly, invade and damage surrounding normal tissues. Cells sloughed from such tumors reach distant sites via blood/lymph, start new tumors (Metastasis - most feared property).
  • Causes of Cancer (Carcinogens): Agents that cause transformation of normal cells into cancerous cells.
    • Physical Carcinogens: Ionizing radiation (X-rays, gamma rays), Non-ionizing radiation (UV rays).
    • Chemical Carcinogens: Tobacco smoke (major cause of lung cancer), vinyl chloride, nicotine, caffeine, etc.
    • Biological Carcinogens: Oncogenic viruses (cancer-causing viruses), have viral oncogenes. Cellular oncogenes (c-onc) or proto-oncogenes in normal cells can get activated under certain conditions leading to cancerous transformation.
  • Cancer Detection and Diagnosis:
    • Biopsy & Histopathological studies: A piece of suspected tissue is cut, stained, examined under microscope.
    • Blood & Bone Marrow Tests: For increased cell counts (leukemias).
    • Imaging Techniques: Radiography (X-rays), CT (Computed Tomography), MRI (Magnetic Resonance Imaging) - useful for internal organ cancers. CT uses X-rays for 3D image. MRI uses magnetic fields and non-ionizing radiation.
    • Antibodies against cancer-specific antigens.
    • Molecular Biology Techniques: To detect genes in individuals with inherited susceptibility.
  • Treatment of Cancer:
    • Surgery: Removal of tumor mass.
    • Radiotherapy: Tumor cells irradiated lethally, taking care to protect surrounding normal tissues.
    • Chemotherapy: Use of cytotoxic drugs to kill cancer cells. Have side effects (hair loss, anaemia). Often used in combination.
    • Immunotherapy: Using biological response modifiers like α-interferon which activate the immune system to help destroy the tumor.

6. Drugs and Alcohol Abuse:

  • Commonly abused drugs include: Opioids, Cannabinoids, Coca Alkaloids. Majority obtained from flowering plants, some from fungi.
  • Opioids:
    • Bind to specific opioid receptors in CNS and gastrointestinal tract.
    • Source: Poppy plant (Papaver somniferum) latex.
    • Example: Heroin (Smack) - chemically diacetylmorphine. White, odourless, bitter crystalline compound.
    • Mode of Intake: Snorting, injection.
    • Effect: Depressant, slows down body functions. Morphine (from latex) is an effective sedative and painkiller, used post-surgery.
  • Cannabinoids:
    • Interact with cannabinoid receptors mainly in the brain.
    • Source: Inflorescences of Cannabis sativa plant. Flower tops, leaves, resin used to produce Marijuana, Hashish, Charas, Ganja.
    • Mode of Intake: Inhalation, oral ingestion.
    • Effect: Affect cardiovascular system, known for effects on mood, perception.
  • Coca Alkaloids (Cocaine):
    • Source: Coca plant (Erythroxylum coca), native to South America.
    • Mode of Intake: Usually snorted.
    • Effect: Interferes with transport of neurotransmitter dopamine. Potent stimulant action on CNS, producing euphoria, increased energy. Excessive dosage causes hallucinations. Crack is a form of cocaine.
  • Other Abused Substances:
    • Atropa belladonna, Datura - Hallucinogenic properties.
    • Barbiturates, Amphetamines, Benzodiazepines - Used as medicines for mental illness (depression, insomnia), often abused. LSD (Lysergic acid diethylamide) from fungus Claviceps purpurea.
  • Smoking:
    • Source: Tobacco (leaves).
    • Active Ingredient: Nicotine (alkaloid).
    • Mode of Intake: Smoking, chewing, snuff.
    • Effect: Stimulates adrenal gland to release adrenaline and nor-adrenaline -> increases blood pressure and heart rate. Associated with cancers (lung, urinary bladder, throat), bronchitis, emphysema, coronary heart disease, gastric ulcer. Smoking increases CO content in blood, reduces concentration of haembound oxygen -> oxygen deficiency.
  • Adolescence and Drug/Alcohol Abuse:
    • Adolescence (12-18 years) is vulnerable phase.
    • Causes: Curiosity, need for adventure/excitement, experimentation, peer pressure, stress relief, family problems, unstable family structure.
  • Addiction and Dependence:
    • Addiction: Psychological attachment to effects like euphoria, temporary well-being associated with drugs/alcohol. Drives people to take them even when not needed, or self-destructively.
    • Dependence: Tendency of the body to manifest unpleasant Withdrawal Syndrome if regular dose is abruptly discontinued (shakiness, anxiety, nausea, sweating). Leads user to resume use. Dependence leads the user to ignore social norms.
  • Effects of Drug/Alcohol Abuse:
    • Immediate: Reckless behaviour, vandalism, violence.
    • Long-term: Damage to nervous system, liver cirrhosis (alcohol). Drop in academic performance, social isolation, depression, fatigue, aggressive behaviour, financial issues, health complications.
    • IV drug users risk infections like AIDS and Hepatitis B.
    • Use during pregnancy affects foetus.
    • Misuse of drugs by sportspersons (narcotic analgesics, anabolic steroids, diuretics).
  • Prevention and Control:
    • Avoid undue peer pressure.
    • Education and counselling.
    • Seeking help from parents and peers.
    • Looking for danger signs (alert parents/teachers).
    • Seeking professional and medical help (psychologists, psychiatrists, de-addiction centres).

This chapter covers a wide range of topics fundamental to human biology and public health. Ensure you remember the specifics, especially for objective questions.

Multiple Choice Questions (MCQs)

  1. The Widal test is used for the diagnosis of which disease?
    (a) Pneumonia
    (b) Typhoid
    (c) Malaria
    (d) Amoebiasis

  2. Which of the following provides cell-mediated immunity (CMI)?
    (a) B-lymphocytes
    (b) T-lymphocytes
    (c) Macrophages
    (d) Neutrophils

  3. The toxic substance 'Haemozoin', responsible for chills and high fever in malaria, is released during:
    (a) Rupture of liver cells
    (b) Entry of sporozoites into blood
    (c) Rupture of Red Blood Cells (RBCs)
    (d) Formation of gametocytes

  4. Which type of antibody is abundantly found in colostrum (mother's first milk)?
    (a) IgG
    (b) IgE
    (c) IgM
    (d) IgA

  5. HIV primarily attacks which of the following cells in the human body?
    (a) B-lymphocytes
    (b) Helper T-lymphocytes (TH cells)
    (c) Cytotoxic T-lymphocytes
    (d) Macrophages (initially, but major depletion is of TH)

  6. The property by which malignant tumor cells invade distant sites is called:
    (a) Metastasis
    (b) Contact inhibition
    (c) Benign growth
    (d) Neoplasia

  7. Heroin (Smack) is derived from which plant?
    (a) Cannabis sativa
    (b) Erythroxylum coca
    (c) Papaver somniferum
    (d) Atropa belladonna

  8. Which of the following acts as a physiological barrier to the entry of microorganisms in the human body?
    (a) Skin
    (b) Mucus coating
    (c) Acid in the stomach
    (d) Interferons

  9. Graft rejection during organ transplantation is primarily due to:
    (a) Humoral immune response
    (b) Cell-mediated immune response
    (c) Innate immune response
    (d) Passive immunity

  10. Ringworm disease in humans is caused by:
    (a) Bacteria
    (b) Virus
    (c) Protozoan
    (d) Fungus

Answer Key:

  1. (b) Typhoid
  2. (b) T-lymphocytes
  3. (c) Rupture of Red Blood Cells (RBCs)
  4. (d) IgA
  5. (b) Helper T-lymphocytes (TH cells)
  6. (a) Metastasis
  7. (c) Papaver somniferum
  8. (c) Acid in the stomach
  9. (b) Cell-mediated immune response
  10. (d) Fungus

Study these notes thoroughly. Understanding the mechanisms and key terms is vital for your exams. Good luck!

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