Human Health and Diseases
'The IMMUNE SYSTEM is the body's personal army — it distinguishes SELF from NON-SELF and eliminates threats with remarkable precision.'
1. Chapter Overview
This chapter explores HEALTH and DISEASE from a biological perspective. Topics include: COMMON HUMAN DISEASES (bacterial, viral, protozoan, helminthic — their pathogens, symptoms, and prevention), the IMMUNE SYSTEM (innate and acquired immunity, active and passive immunity, B-cells and T-cells, antibodies), AIDS (HIV structure, transmission, progression, prevention), CANCER (types, causes, detection, treatment), and DRUGS AND ALCOHOL ABUSE (types of drugs, effects, addiction, prevention).
2. Common Human Diseases
Bacterial Diseases
| Disease | Pathogen | Transmission | Symptoms | Prevention |
|---|---|---|---|---|
| Typhoid | Salmonella typhi | Contaminated food/water | High fever (up to 2 weeks), abdominal pain, intestinal perforation | Sanitation, vaccination |
| Pneumonia | Streptococcus pneumoniae, Haemophilus influenzae | Airborne droplets | Fever, chills, cough with phlegm, difficulty breathing | Vaccination |
| Dysentery | Shigella, E. coli | Contaminated food/water | Diarrhoea with blood/mucus | Hygiene |
| Tetanus | Clostridium tetani | Wound infection | Muscle spasms, lockjaw | Vaccination |
Viral Diseases
| Disease | Pathogen | Transmission | Symptoms |
|---|---|---|---|
| Common cold | Rhinovirus | Airborne droplets | Nasal congestion, sore throat, cough |
| Influenza | Influenza virus | Airborne droplets | Fever, body aches, fatigue |
| Dengue | Dengue virus (Flavivirus) | Mosquito (Aedes) | High fever, severe joint pain, rash, haemorrhagic fever |
| Hepatitis B | HBV (Hepadnavirus) | Blood, body fluids | Liver inflammation, jaundice, cirrhosis, cancer |
| Rabies | Rabies virus | Animal bite (dog) | Hydrophobia, paralysis, FATAL once symptoms appear |
Protozoan and Helminthic Diseases
| Disease | Pathogen | Vector/Transmission | Symptoms |
|---|---|---|---|
| Malaria | Plasmodium (P. vivax, P. falciparum, etc.) | Anopheles mosquito | Fever alternating with chills, anaemia |
| Amoebiasis | Entamoeba histolytica | Contaminated food/water | Abdominal pain, dysentery |
| Ascariasis | Ascaris lumbricoides (roundworm) | Contaminated soil/food | Abdominal pain, malnutrition |
| Filariasis (Elephantiasis) | Wuchereria bancrofti | Culex mosquito | Lymphatic obstruction, swelling of limbs |
3. The Immune System
Innate Immunity (Non-Specific)
- PRESENT AT BIRTH — provides FIRST LINE OF DEFENCE.
- Barriers: Physical (skin, mucus), Physiological (stomach acid, lysozyme in tears), Cellular (phagocytes — neutrophils, macrophages), Inflammatory response.
Acquired Immunity (Specific)
- DEVELOPED after exposure to a pathogen — has MEMORY.
- Components: B-cells (BONE MARROW-derived) and T-cells (THYMUS-derived).
- B-cells: Produce ANTIBODIES (humoral immunity). Memory B-cells provide long-term immunity.
- T-cells: CELL-MEDIATED immunity. Helper T-cells (CD4⁺) ACTIVATE B-cells. Killer T-cells (CD8⁺) DESTROY infected cells.
Active vs Passive Immunity
| Type | Antibody Source | Duration | Onset | Example |
|---|---|---|---|---|
| Active (Natural) | Self — after infection | LONG (memory) | SLOW | Recovering from COVID-19 |
| Active (Artificial) | Self — after vaccination | LONG (memory) | SLOW | Vaccination |
| Passive (Natural) | Mother to foetus/infant (via placenta/milk) | SHORT | FAST | Maternal antibodies in newborn |
| Passive (Artificial) | External source — ready-made antibodies | SHORT | FAST | Anti-tetanus serum, snake antivenom |
4. AIDS (Acquired Immunodeficiency Syndrome)
- Pathogen: HIV (Human Immunodeficiency Virus — a RETROVIRUS).
- Structure: RNA genome + REVERSE TRANSCRIPTASE enzyme (converts RNA → DNA).
- Transmission: (1) Sexual contact. (2) Blood transfusion / contaminated needles. (3) Mother to child (during pregnancy, birth, or breastfeeding).
- NOT transmitted by: Casual contact, hugging, sharing utensils, mosquito bites.
Progression
- Acute stage (2-4 weeks): Flu-like symptoms. High viral load.
- Chronic stage (latency) : Virus replicating slowly. CD4⁺ count GRADUALLY decreases. Patient MAY appear healthy for years.
- AIDS (CD4⁺ count < 200 cells/μL): Immune system SEVERELY compromised. OPPORTUNISTIC INFECTIONS (tuberculosis, pneumonia, certain cancers).
Prevention and Treatment
- No CURE — but ANTIRETROVIRAL THERAPY (ART) controls viral replication.
- Prevention: SAFE SEX (condoms), needle exchange programmes, blood screening, preventing mother-to-child transmission.
- 'The ELISA test detects HIV ANTIBODIES. The PCR test detects HIV RNA directly — used for early diagnosis.'
5. Cancer
Types
- Benign: LOCALISED — does NOT spread. Usually REMOVABLE by surgery.
- Malignant: INVASIVE — spreads to surrounding tissues. CAN metastasise (spread via blood/lymph).
- Carcinomas: Epithelial cells (lungs, breast, colon, skin). Sarcomas: Connective tissue (bone, muscle). Leukaemias: Blood-forming tissues. Lymphomas: Lymphatic system.
Causes
- Chemical carcinogens: Tobacco smoke (lung cancer), asbestos (mesothelioma).
- Physical carcinogens: UV radiation (skin cancer), ionising radiation.
- Biological: Oncogenic viruses (HPV → cervical cancer, Hepatitis B → liver cancer).
Detection and Treatment
- Detection: MRI, CT scan, biopsy, PET scan, mammography, Pap smear.
- Treatment: Surgery, RADIATION THERAPY, CHEMOTHERAPY, IMMUNOTHERAPY, TARGETED THERAPY.
- Two key genes: ONCOGENES (promote cancer — mutated proto-oncogenes). TUMOUR SUPPRESSOR GENES (p53 — prevent cancer). 'Cancer develops when MULTIPLE mutations accumulate.'
6. Drugs and Alcohol Abuse
Commonly Abused Substances
| Substance | Source | Effect | Health Risks |
|---|---|---|---|
| Opioids (heroin, morphine) | Opium poppy | PAIN RELIEF, EUPHORIA | Addiction, respiratory depression, overdose DEATH |
| Cannabinoids (marijuana, hashish) | Cannabis sativa | RELAXATION, altered perception | Impaired memory, addiction, lung damage (if smoked) |
| Cocaine | Coca plant | STIMULANT — intense EUPHORIA | Cardiovascular damage, addiction, stroke |
| Amphetamines | Synthetic | STIMULANT | Insomnia, paranoia, cardiac damage |
| Barbiturates | Synthetic | DEPRESSANT | Sedation, overdose (especially with alcohol) |
| LSD | Ergot fungus | HALLUCINOGEN — altered perception | Bad trips, flashbacks, psychological effects |
| Alcohol | Fermented grains | DEPRESSANT | Liver cirrhosis, addiction, accidents |
Addiction and Dependence
- Psychological dependence: CRAVING — the substance becomes CENTRAL to the person's life.
- Physical dependence: WITHDRAWAL SYMPTOMS when the substance is stopped (nausea, sweating, tremors, anxiety).
Prevention
- Education about consequences. Building SELF-ESTEEM and COPING SKILLS. PEER EDUCATION. Identifying EARLY WARNING SIGNS. Seeking professional HELP (counselling, rehabilitation).
7. Comparison Table: Bacterial vs Viral Diseases
| Feature | Bacterial | Viral |
|---|---|---|
| Pathogen type | Bacteria (prokaryote) | Virus (non-living outside host) |
| Treatable with antibiotics? | YES | NO (except some antivirals) |
| Vaccine available? | Some (tetanus, typhoid) | Some (hepatitis, rabies, flu) |
| Examples | Typhoid, Tetanus, Pneumonia | AIDS, Common cold, Dengue |
8. Common Mistakes
- Antibiotics do NOT work against viruses: Antibiotics kill BACTERIA. They are USELESS against viral infections like the common cold or flu.
- AIDS is NOT transmitted by casual contact: Shaking hands, hugging, or sharing food with an HIV-positive person is SAFE.
- Cancer is NOT a single disease: There are over 200 types of cancer — each with different causes, treatments, and prognoses.
- Not all tumours are cancerous: BENIGN tumours do NOT spread or invade other tissues — they are NOT cancer.
9. CBSE Exam Focus
- Common diseases — bacterial (typhoid, pneumonia), viral (common cold, hepatitis), protozoan (malaria, amoebiasis)
- Immune system — innate vs acquired, active vs passive immunity, B-cells and T-cells
- AIDS — HIV structure, transmission, progression, prevention, diagnosis (ELISA)
- Cancer — types (benign vs malignant), carcinogens, oncogenes and tumour suppressor genes
- Drugs and alcohol abuse — types of drugs, effects, prevention
10. Self-Test
Q1: Differentiate between active and passive immunity. A1: Active: Body PRODUCES its own antibodies after exposure to antigen (infection or vaccination). LONG-LASTING. Passive: READY-MADE antibodies are transferred (mother to child, anti-snake venom). IMMEDIATE but SHORT-LIVED.
Q2: Which cells are primarily destroyed by HIV? What is the consequence? A2: HIV primarily destroys HELPER T-CELLS (CD4⁺ T-cells). These cells are CRUCIAL for activating both B-cells (antibody production) and killer T-cells. Their destruction leads to PROGRESSIVE IMMUNE DEFICIENCY — the hallmark of AIDS.
Q3: Name the vector and pathogen for malaria. A3: Vector: Female Anopheles MOSQUITO. Pathogen: Plasmodium (protozoan) — P. vivax, P. falciparum, etc.
Q4: What is the difference between benign and malignant tumours? A4: Benign: LOCALISED, does NOT spread, usually REMOVABLE. Malignant: INVASIVE, spreads to neighbouring tissues and can METASTASISE to distant sites — LIFE-THREATENING.
Q5: Name TWO bacterial and TWO viral diseases. A5: Bacterial: Typhoid, Pneumonia, Tetanus (any 2). Viral: Common cold, AIDS, Influenza, Hepatitis B (any 2).
11. Conclusion
Human health and disease is about the BODY'S DEFENCES and their FAILURE:
- IMMUNE SYSTEM: 'A COMPLEX network of cells, tissues, and organs — working together to defend the body against pathogens.'
- AIDS: 'A MODERN PANDEMIC — caused by a virus that attacks the immune system itself. Preventable but not curable.'
- CANCER: 'Uncontrolled cell division — caused by genetic mutations. Early detection SAVES lives.'
- 'Understanding our immune system is the first step to understanding how to keep our bodies HEALTHY and fight disease.'
