Class 12 Biology Notes Chapter 8 (Human Health and Diseases) – Examplar Problems Book

Detailed Notes with MCQs of Chapter 8: Human Health and Diseases. This is a crucial chapter, not just for your board exams but also frequently tested in various government competitive exams due to its direct relevance to public health. We'll cover the key concepts based on your NCERT Exemplar understanding. Pay close attention.

Human Health and Diseases: Key Concepts & Notes

1. Health:

• Defined by WHO as 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, rest, habits (smoking, alcohol).
• Good health maintenance involves: Balanced diet, personal hygiene, regular exercise, awareness about diseases, proper waste disposal, vector control, and immunization.

2. Disease:

• Any condition that interferes with the normal functioning of the body or mind.
• Broadly classified into:
  • Infectious Diseases: Easily transmitted from one person to another (e.g., Typhoid, Common Cold, Malaria, AIDS). Caused by pathogens (bacteria, viruses, fungi, protozoans, helminths).
  • Non-infectious Diseases: Cannot be transmitted (e.g., Cancer, Diabetes, Hypertension, Genetic disorders).

3. Common Infectious Diseases in Humans:

*   **Bacterial Diseases:**
    *   **Typhoid:**
        *   Causative Agent: *Salmonella typhi* (bacterium).
        *   Transmission: Contaminated food and water.
        *   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**.
    *   **Pneumonia:**
        *   Causative Agent: *Streptococcus pneumoniae* and *Haemophilus influenzae* (bacteria).
        *   Transmission: Inhaling droplets/aerosols from an infected person, sharing utensils.
        *   Symptoms: Infection of alveoli (air sacs) of lungs; alveoli get filled with fluid leading to respiratory problems. Fever, chills, cough, headache. In severe cases, lips and fingernails may turn greyish to bluish.
    *   **Others:** Dysentery, Plague, Diphtheria.

*   **Viral Diseases:**
    *   **Common Cold:**
        *   Causative Agent: Rhinoviruses (group of viruses).
        *   Transmission: Inhaling droplets from cough/sneeze, contaminated objects (pens, books, etc.).
        *   Symptoms: Infects nose and respiratory passage (but NOT lungs). Nasal congestion and discharge, sore throat, hoarseness, cough, headache, tiredness. Usually lasts 3-7 days.
    *   **Others:** Polio, Influenza, Mumps, Measles, Dengue, Chikungunya, AIDS (discussed separately).

*   **Protozoan Diseases:**
    *   **Malaria:**
        *   Causative Agent: *Plasmodium* species (*P. vivax, P. malariae, P. falciparum*). Malignant malaria caused by *P. falciparum* is most serious and can be fatal.
        *   Transmission: Bite of infected female *Anopheles* mosquito (vector).
        *   Life Cycle: Involves two hosts - humans and mosquitoes.
            *   Human: Sporozoites injected -> Liver cells (multiply) -> Attack RBCs (multiply asexually, rupture RBCs releasing **haemozoin** toxin responsible for chills and high fever recurring every 3-4 days) -> Gametocytes form in RBCs.
            *   Mosquito: Takes up gametocytes with blood meal -> Fertilization and development in mosquito gut -> Sporozoites stored in salivary glands.
        *   Symptoms: High fever recurring cyclically, chills, headache.
    *   **Amoebiasis (Amoebic Dysentery):**
        *   Causative Agent: *Entamoeba histolytica* (protozoan).
        *   Transmission: Contaminated food and water (faecal-oral route). Houseflies act as mechanical carriers.
        *   Symptoms: Constipation, abdominal pain and cramps, stools with excess mucus and blood clots.

*   **Helminthic Diseases:**
    *   **Ascariasis:**
        *   Causative Agent: *Ascaris lumbricoides* (common roundworm).
        *   Transmission: Contaminated water, vegetables, fruits (eggs of parasite excreted with faeces).
        *   Symptoms: Internal bleeding, muscular pain, fever, anaemia, blockage of the intestinal passage.
    *   **Filariasis (Elephantiasis):**
        *   Causative Agent: *Wuchereria bancrofti* and *Wuchereria malayi* (filarial worms).
        *   Transmission: Bite of female *Culex* mosquito (vector).
        *   Symptoms: Chronic inflammation of organs where they live (usually lymphatic vessels of lower limbs). Leads to gross deformities, hence called elephantiasis. Genital organs can also be affected.

*   **Fungal Diseases:**
    *   **Ringworm:**
        *   Causative Agent: Fungi belonging to 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).

4. Prevention and Control of Infectious Diseases:

• Maintenance of personal and public hygiene (cleanliness, safe drinking water, proper waste disposal).
• Avoiding close contact with infected persons/belongings.
• Control/Elimination of vectors (e.g., mosquitoes - avoid water stagnation, use mosquito nets, repellents, introduce larvivorous fish like Gambusia).
• Use of vaccines and immunization programmes.
• Use of antibiotics and other drugs (judiciously).

5. Immunity:

• Overall ability of the host to fight disease-causing organisms.
• Two types:
  • Innate Immunity (Non-specific): Present at birth. Consists of four types of barriers:
    • Physical Barriers: Skin, Mucus coating (respiratory, gastrointestinal, urogenital tracts).
    • Physiological Barriers: Acid in stomach, Saliva in mouth, Tears from eyes (contain lysozyme).
    • Cellular Barriers: Certain leukocytes (WBCs) like Polymorphonuclear leukocytes (PMNL-neutrophils), Monocytes, Natural killer (NK) cells (type of lymphocyte), Macrophages. Phagocytose microbes.
    • Cytokine Barriers: Virus-infected cells secrete proteins called interferons which protect non-infected cells from further viral infection.
  • Acquired Immunity (Specific): Pathogen-specific. Characterized by memory. When 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.
    • Mediated by lymphocytes (B-lymphocytes and T-lymphocytes).
    • Humoral Immune Response (Antibody-mediated): Mediated by B-lymphocytes. Produce proteins called antibodies in response to pathogens in blood/fluids.
      • Antibodies: Y-shaped structure (H₂L₂ - 2 heavy chains, 2 light chains). Different types: IgA, IgM, IgE, IgG. IgA present in colostrum (first milk). IgG crosses placenta. IgE involved in allergic reactions.
    • Cell-mediated Immune Response (CMI): Mediated by T-lymphocytes.
      • Helper T-cells: Help B-cells produce antibodies.
      • Cytotoxic T-cells: Directly kill infected cells.
      • Responsible for graft rejection. Tissue matching/blood group matching essential before transplantation.

6. Types of Acquired Immunity:

• Active Immunity: Host produces antibodies in response to antigens (live/dead microbes or proteins). Slow but long-lasting.
  • Natural Active: Develops during natural infection.
  • Artificial Active: Develops after vaccination (introduction of weakened/inactivated pathogens or antigens).
• Passive Immunity: Readymade antibodies are directly given. Provides immediate relief but is short-lived.
  • Natural Passive: Antibodies from mother to foetus (IgG via placenta) or infant (IgA via colostrum).
  • Artificial Passive: Injection of pre-formed antibodies/antitoxin (e.g., anti-tetanus serum, anti-snake venom).

7. Vaccination and Immunization:

• Principle based on the memory property of the immune system.
• A preparation of antigenic proteins of pathogen or inactivated/weakened pathogen (vaccine) is introduced.
• This generates antibodies and memory B and T-cells.
• On subsequent actual infection, memory cells recognize the pathogen quickly and mount a massive secondary response.
• Modern methods: Recombinant DNA technology allows production of antigenic polypeptides (e.g., Hepatitis B vaccine from yeast).

8. Allergies:

• Exaggerated response of the immune system to certain antigens present in the environment (allergens - e.g., pollen, dust mites, animal dander).
• Antibodies produced: IgE type.
• Chemicals released: Histamine, serotonin from mast cells.
• Symptoms: Sneezing, watery eyes, running nose, difficulty breathing.
• Treatment: Antihistamines, adrenaline, steroids.

9. Autoimmunity:

• Immune system attacks self-cells due to genetic/unknown reasons. Body fails to differentiate between 'self' and 'non-self'.
• Example: Rheumatoid arthritis.

10. Immune System in the Body:

• Includes lymphoid organs, tissues, cells, and soluble molecules (antibodies).
• Lymphoid Organs:
  • Primary: Bone marrow and Thymus. Immature lymphocytes differentiate into antigen-sensitive lymphocytes.
  • Secondary: 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 and memory cells.
• MALT (Mucosal Associated Lymphoid Tissue): Located within lining of major tracts (respiratory, digestive, urogenital). Constitutes about 50% of lymphoid tissue.

11. AIDS (Acquired Immuno Deficiency Syndrome):

• Caused by: Human Immunodeficiency Virus (HIV), a retrovirus (has RNA genome and reverse transcriptase enzyme).
• Transmission: Sexual contact, contaminated blood/blood products, sharing infected needles, infected mother to child (placenta). NOT by mere touch or physical contact.
• Mechanism: HIV enters helper T-lymphocytes (TH cells), replicates (RNA -> DNA via reverse transcriptase -> incorporates into host DNA -> directs synthesis of new viruses), and destroys them. This leads to a progressive decrease in TH cell count.
• Symptoms: Person suffers from infections (bacteria like Mycobacterium, viruses, fungi, parasites like Toxoplasma) that could otherwise be overcome. Bouts of fever, diarrhoea, weight loss. Leads to severe immunodeficiency.
• Diagnosis: ELISA (Enzyme Linked Immunosorbent Assay). Western Blotting is confirmatory.
• Treatment: Anti-retroviral drugs (partially effective, prolong life but don't prevent death).
• Prevention: Education, safe sex practices, screening blood, disposable needles, advocating against drug abuse. NACO (National AIDS Control Organisation) and NGOs play vital roles.

12. Cancer:

• Uncontrolled cell growth and division. Normal cells show contact inhibition (contact with other cells inhibits their further growth), which is lost in cancer cells.
• Tumors: Masses of cells.
  • Benign: Remain confined to original location, don't spread. Cause little damage generally.
  • Malignant: Proliferating cells (neoplastic/tumor cells) grow rapidly, invade and damage surrounding normal tissues. Cells sloughed from such tumors reach distant sites via blood, forming new tumors (metastasis - most feared property).
• Causes (Carcinogens): Agents causing cancer.
  • Physical: Ionizing radiations (X-rays, gamma rays), Non-ionizing (UV rays).
  • Chemical: Tobacco smoke (major cause of lung cancer), vinyl chloride, nicotine, caffeine, etc.
  • Biological: Oncogenic viruses (cancer-causing viruses). Cellular oncogenes (c-onc) or proto-oncogenes in normal cells can get activated under certain conditions.
• Detection and Diagnosis: Biopsy and histopathological studies, blood/bone marrow tests (leukemia), imaging (Radiography, CT scan, MRI), antibodies against cancer-specific antigens. Molecular biology techniques to detect cancer-related genes.
• Treatment:
  • Surgery: Removal of tumor mass.
  • Radiation therapy: Tumor cells irradiated lethally, minimizing damage to surrounding normal tissue.
  • Chemotherapy: Use of cytotoxic drugs to kill cancer cells (often have side effects like hair loss, anaemia).
  • Immunotherapy: Use of biological response modifiers like α-interferon to activate the immune system to destroy the tumor.

13. Drugs and Alcohol Abuse:

• Adolescence is a vulnerable period. Curiosity, peer pressure, excitement, experimentation, stress relief are common causes.
• Opioids:
  • Bind to opioid receptors in CNS and GIT.
  • Source: Poppy plant (Papaver somniferum) latex.
  • Example: Morphine (sedative, painkiller), Heroin (smack - diacetylmorphine, white, bitter, crystalline, obtained by acetylation of morphine).
  • Mode of intake: Snorting, injection.
  • Effect: Depressant, slows down body functions.
• Cannabinoids:
  • Interact with cannabinoid receptors 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. Hallucinogenic properties (alter thoughts, perceptions, feelings).
• Coca Alkaloids (Cocaine):
  • Source: Coca plant (Erythroxylum coca), native to South America.
  • Mode of intake: Snorting.
  • Effect: Interferes with dopamine transport. Potent CNS stimulant, produces euphoria, increased energy. Excessive dosage causes hallucinations. Crack is a form.
• Other abused substances: Atropa belladonna, Datura (hallucinogenic). Barbiturates, amphetamines, benzodiazepines, LSD (Lysergic acid diethylamide) - used as medicines for mental illness but often abused.
• Smoking: Tobacco (chewed, smoked). Contains nicotine (alkaloid). Stimulates adrenal gland (adrenaline, nor-adrenaline release -> increased BP, heart rate). Associated with cancers (lung, urinary bladder, throat), bronchitis, emphysema, coronary heart disease, gastric ulcer.
• Alcohol Abuse: Affects nervous system, liver (cirrhosis).
• Addiction: Psychological attachment to effects like euphoria.
• Dependence: Tendency of the body to manifest unpleasant withdrawal syndrome if regular dose is abruptly discontinued (anxiety, shakiness, nausea, sweating).
• Effects of Abuse: Reckless behaviour, vandalism, violence, drop in academic performance, depression, isolation, family problems, health issues (including risk of infections like AIDS, Hepatitis B if using shared needles).
• Prevention and Control: Avoid undue peer pressure, education/counselling, seek parental/peer help, look for danger signs, seek professional/medical help (psychologists, psychiatrists, de-addiction centres).

Multiple Choice Questions (MCQs):

1. The Widal test is used for the diagnosis of:
   a) Malaria
   b) Pneumonia
   c) Typhoid
   d) Common Cold

2. Which pathogen causes malignant malaria, often fatal?
   a) Plasmodium vivax
   b) Plasmodium malariae
   c) Plasmodium falciparum
   d) Entamoeba histolytica

3. Which of the following provides passive immunity to the infant?
   a) Vaccination with MMR
   b) Antibodies received through colostrum
   c) Recovery from measles infection
   d) Injection of polio vaccine

4. Cell-mediated immunity is primarily provided by:
   a) B-lymphocytes
   b) T-lymphocytes
   c) Neutrophils
   d) Macrophages

5. HIV primarily attacks which of the following cells, leading to immunodeficiency?
   a) B-lymphocytes
   b) Cytotoxic T-lymphocytes
   c) Helper T-lymphocytes (TH cells)
   d) Natural Killer cells

6. The property of cancer cells by which they spread to distant sites in the body is called:
   a) Contact inhibition
   b) Metastasis
   c) Benign growth
   d) Apoptosis

7. Ringworm infection in humans is caused by:
   a) Bacteria
   b) Viruses
   c) Fungi
   d) Helminths

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

9. Which type of antibody is associated with allergic reactions?
   a) IgG
   b) IgA
   c) IgM
   d) IgE

10. Interferons are proteins secreted by virus-infected cells that belong to which type of innate immunity barrier?
    a) Physical barrier
    b) Physiological barrier
    c) Cellular barrier
    d) Cytokine barrier

Answer Key:

1. c) Typhoid
2. c) Plasmodium falciparum
3. b) Antibodies received through colostrum
4. b) T-lymphocytes
5. c) Helper T-lymphocytes (TH cells)
6. b) Metastasis
7. c) Fungi
8. d) Papaver somniferum
9. d) IgE
10. d) Cytokine barrier

Revise these notes thoroughly. Understanding the causative agents, modes of transmission, symptoms, and the principles of immunity is key for your exams. Good luck!