Human Health and Disease Class 12 Notes

Key Concepts & Health Basics

• Health is a state of complete physical, mental, and social well-being, not merely the absence of disease or infirmity.
• Disease refers to any condition that impairs the normal functioning of an organism.
• Pathogens are disease-causing microorganisms (bacteria, viruses, fungi, protozoans, helminths).
• Infectious Diseases can be transmitted from one person to another (e.g., common cold, malaria).
• Non-infectious Diseases cannot be transmitted (e.g., cancer, diabetes, heart disease).
• Immunity is the ability of the host to fight against disease-causing organisms.
• Vaccination/Immunisation is the process of introducing a weakened or inactivated pathogen (vaccine) to stimulate the immune system and build immunity.
• Allergy is an exaggerated response of the immune system to certain antigens present in the environment (allergens).
• Autoimmunity occurs when the immune system mistakenly attacks the body's own healthy cells.
• Cancer is characterized by uncontrolled growth and division of cells, leading to tumor formation.

Common Human Diseases: Causes, Transmission & Symptoms

Understanding common human diseases involves knowing their causative agents, how they spread, and their typical symptoms. This knowledge is crucial for prevention and treatment.

1. Bacterial Diseases:

• Typhoid: Caused by Salmonella typhi. Transmitted via contaminated food and water. Symptoms include sustained high fever (39°C to 40°C), weakness, stomach pain, constipation, headache, and loss of appetite. Widal test is used for diagnosis.
• Pneumonia: Caused by Streptococcus pneumoniae and Haemophilus influenzae. Infects alveoli, filling them with fluid. Transmitted by inhaling droplets from an infected person. Symptoms include fever, chills, cough, headache, and in severe cases, lips and fingernails may turn greyish to bluish.

2. Viral Diseases:

• Common Cold: Caused by Rhinoviruses. Infects nose and respiratory passages (not lungs). Transmitted through droplets from coughing/sneezing. Symptoms include nasal congestion, discharge, sore throat, hoarseness, cough, headache, and fatigue, usually lasting 3-7 days.

3. Protozoan Diseases:

• Malaria: Caused by Plasmodium (P. vivax, P. malariae, P. falciparum – most severe). Transmitted by female Anopheles mosquito. Life cycle involves both human and mosquito hosts. Symptoms include recurring high fever (chills and fever recurring every 3-4 days) and sweating. Malarial parasite requires two hosts to complete its life cycle.
• Amoebiasis (Amoebic Dysentery): Caused by Entamoeba histolytica. Transmitted via contaminated food and water, often by houseflies. Symptoms include constipation, abdominal pain, cramps, and stools with excess mucus and blood clots.

4. Helminthic Diseases:

• Ascariasis: Caused by Ascaris lumbricoides (roundworm). Transmitted via contaminated food, water, and soil. Symptoms include internal bleeding, muscular pain, fever, anaemia, and blockage of intestinal passage.
• Filariasis (Elephantiasis): Caused by Wuchereria bancrofti and W. malayi (filarial worms). Transmitted by female Culex mosquito. Symptoms involve chronic inflammation of lymphatic vessels of lower limbs, leading to gross deformities (elephantiasis).

5. Fungal Diseases:

• Ringworm: Caused by fungi like Microsporum, Trichophyton, and Epidermophyton. Highly contagious. Transmitted via soil or infected individuals/articles. Symptoms include dry, scaly lesions on skin, nails, and scalp, often accompanied by intense itching.

Immunity: Our Body's Defence Mechanisms

Immunity

The ability of the host to fight against disease-causing organisms (pathogens) conferred by the immune system.

Innate Immunity

Non-specific defence present from birth, providing different types of barriers to the entry of foreign agents.

Acquired Immunity

Pathogen-specific immunity developed during an individual's lifetime, characterized by memory.

Antibody

Protein molecules (immunoglobulins, e.g., IgA, IgM, IgG, IgE, IgD) produced by B-lymphocytes in response to antigens. They have a Y-shaped structure with two light and two heavy chains.

Antigen

Any substance that elicits an immune response, typically a foreign molecule.

Active Immunity

Immunity acquired when the body produces its own antibodies in response to an antigen (e.g., due to infection or vaccination).

Passive Immunity

Immunity acquired when pre-formed antibodies are given to the body (e.g., from mother to foetus or through antitoxins).

Cell-mediated Immunity (CMI)

Immune response mediated by T-lymphocytes, primarily targeting infected cells, cancer cells, and foreign tissue grafts.

Humoral Immunity (Antibody-mediated)

Immune response mediated by B-lymphocytes that produce antibodies circulating in body fluids (humors) to neutralize pathogens.

Innate vs. Acquired Immunity

Immune System Malfunctions & Major Health Challenges

The immune system, while usually protective, can sometimes malfunction or face overwhelming challenges.

Allergies: An exaggerated response of the immune system to certain environmental substances (allergens) like pollen, dust mites, or animal dander. Symptoms include sneezing, watery eyes, running nose, and difficulty breathing. Mediated by IgE antibodies and chemicals like histamine and serotonin released from mast cells.

Autoimmunity: A disorder where the immune system loses the ability to distinguish between 'self' and 'non-self' and attacks the body's own tissues. Examples include rheumatoid arthritis and multiple sclerosis.

AIDS (Acquired ImmunoDeficiency Syndrome): Caused by the Human Immunodeficiency Virus (HIV), a retrovirus. HIV primarily attacks helper T-lymphocytes (CD4+ T-cells), crucial for immune responses. This leads to a severe immunodeficiency, making the patient susceptible to various opportunistic infections (e.g., Mycobacterium, Toxoplasma, viruses, fungi) and certain cancers. Transmission occurs through sexual contact, contaminated blood/needles, or from infected mother to child. No cure exists, but antiretroviral drugs can prolong life.

Cancer: An abnormal, uncontrolled proliferation of cells. Normal cells exhibit contact inhibition, preventing uncontrolled growth. Cancerous cells lose this property. Tumors can be benign (localized, non-spreading) or malignant (invade surrounding tissues, metastasize to distant sites). Carcinogens (physical, chemical, biological agents) can cause cancer. Detection involves biopsy, radiography, CT scans, MRI, and molecular biology techniques. Treatment includes surgery, radiotherapy, chemotherapy, and immunotherapy.

Drugs and Alcohol Abuse

Substance abuse is a significant health and social problem. Drugs of abuse primarily affect the central nervous system and behaviour.

1. Opioids: Derived from the poppy plant (Papaver somniferum). Examples: Morphine, Heroin (diacetylmorphine). Act on opioid receptors in CNS and gastrointestinal tract. Heroin is a depressant, slowing down body functions.

2. Cannabinoids: Obtained from Cannabis sativa. Examples: Marijuana, hashish, charas, ganja. Act on cannabinoid receptors in the brain. Affect cardiovascular system.

3. Stimulants: Examples: Cocaine (from coca plant Erythroxylum coca), Amphetamines. Cocaine interferes with dopamine transport, causing euphoria and increased energy. Excessive doses lead to hallucinations.

4. Hallucinogens: Examples: LSD (Lysergic acid diethylamide), certain fungi, Atropa belladonna, Datura. Alter thoughts, perceptions, and feelings.

Adolescence and Drug/Alcohol Abuse: Adolescence is a vulnerable period due to pressure to experiment, curiosity, stress, and desire for excitement. Effects include reckless behaviour, violence, poor academic performance, depression, and social isolation. Intravenous drug abuse increases risk of AIDS and Hepatitis B.

Prevention and Control: Education, avoiding peer pressure, seeking help from parents/peers, professional help, and identifying warning signs are crucial steps to prevent and control substance abuse.

Conceptual Example: Immune Response Scenario

• Scenario: A child receives a vaccine for measles. A few weeks later, the child is exposed to the measles virus. Explain the immune response. Explanation: The measles vaccine contains attenuated (weakened) measles virus, acting as an antigen. Upon vaccination, the child's immune system (B and T lymphocytes) recognizes this antigen and mounts a primary immune response, producing specific antibodies and memory cells. When the child is later exposed to the actual measles virus, the pre-existing memory cells rapidly recognize the pathogen. This triggers a much faster and stronger secondary immune response, producing a large number of specific antibodies quickly, effectively neutralizing the virus before it can cause disease symptoms. This is an example of active acquired immunity.

Exam Mastery Tips for Human Health & Disease

This chapter is highly scoring and often features direct questions. Focus on:

• Causative Agents & Diseases: Create flashcards for pathogens and the diseases they cause (e.g., Salmonella typhi -> Typhoid). Be precise with scientific names.
• Life Cycles: Understand the life cycle of Plasmodium (Malaria) and Wuchereria (Filariasis), noting the hosts and stages. Diagrams are key!
• Immunity Types: Clearly differentiate between innate/acquired, active/passive, and humoral/cell-mediated immunity with examples.
• Antibody Structure: Practice drawing and labelling the Y-shaped antibody structure. Mention the types of antibodies (IgA, IgM, IgG, IgE, IgD) and their functions.
• AIDS & Cancer: Know the causative agent, transmission, target cells, and symptoms/effects for AIDS. For cancer, understand contact inhibition, benign vs. malignant tumors, metastasis, and common detection/treatment methods.
• Substance Abuse: Focus on the source plant, specific drug names, their effects (depressant/stimulant/hallucinogenic), and methods of prevention.

Practice Questions with Solutions

• Q: Name the causative agent of Typhoid and the diagnostic test for it. A: Causative agent: Salmonella typhi. Diagnostic test: Widal test.
• Q: Differentiate between active and passive immunity with one example each. A: Active immunity: Body produces its own antibodies (e.g., vaccination). Passive immunity: Pre-formed antibodies are given (e.g., antibodies from mother to foetus).
• Q: What is the primary target cell for HIV in the human body? A: Helper T-lymphocytes (CD4+ T-cells).
• Q: Give two examples of drugs that are stimulants and state their effect. A: Cocaine and Amphetamines. They increase alertness, activity, and can cause euphoria.

Frequently Asked Questions