REVISION SUMMARY: Human Health and Disease (Chapter 7)
1. Chapter at a Glance
- Health is defined as a state of complete physical, mental and social well-being; disease occurs when one or more organs or systems are adversely affected, showing signs and symptoms.
- Diseases are grouped as infectious (transmitted from one person to another) and non-infectious (e.g., cancer); pathogens include bacteria, viruses, protozoans, helminths and fungi.
- Common infectious diseases include typhoid (Salmonella typhi), pneumonia (Streptococcus pneumoniae), common cold (rhinoviruses), malaria (Plasmodium spp.), amoebiasis (Entamoeba histolytica), ascariasis (Ascaris), filariasis (Wuchereria) and ringworm (Microsporum/Trichophyton).
- Immunity comprises innate (non-specific barriers present at birth) and acquired (pathogen-specific with memory); acquired immunity is mediated by B-lymphocytes (antibodies) and T-lymphocytes (CMI).
- Active immunity is produced by the host after exposure to antigens; passive immunity involves direct transfer of ready-made antibodies.
- Vaccination introduces antigenic proteins or weakened pathogens to generate memory cells; allergies are exaggerated IgE responses to allergens, while autoimmunity involves attack on self-cells.
- AIDS is caused by HIV (retrovirus) leading to progressive loss of helper T-lymphocytes; cancer results from loss of contact inhibition, forming benign or malignant tumours with metastasis.
- Drug/alcohol abuse leads to addiction, dependence and withdrawal; prevention requires education, counselling and avoidance of peer pressure.
2. Definitions and Laws (Exact NCERT Framing)
- Health: “a state of complete physical, mental and social well-being.”
- Disease: “When the functioning of one or more organs or systems of the body is adversely affected, characterised by appearance of various signs and symptoms, we say that we are not healthy, i.e., we have a disease.”
- Pathogens: “Such disease-causing organisms are called pathogens.”
- Immunity: “This overall ability of the host to fight the disease-causing organisms, conferred by the immune system is called immunity.”
- Innate immunity: “Innate immunity is non-specific type of defence, that is present at the time of birth.”
- Acquired immunity: “Acquired immunity, on the other hand is pathogen specific. It is characterised by memory.”
- Active immunity: “When a host is exposed to antigens… antibodies are produced in the host body. This type of immunity is called active immunity.”
- Passive immunity: “When ready-made antibodies are directly given to protect the body against foreign agents, it is called passive immunity.”
- Allergy: “The exaggerated response of the immune system to certain antigens present in the environment is called allergy.”
- Auto-immune disease: “sometimes, due to genetic and other unknown reasons, the body attacks self-cells. This results in damage to the body and is called auto-immune disease.”
- AIDS: “The word AIDS stands for Acquired Immuno Deficiency Syndrome. This means deficiency of immune system, acquired during the lifetime of an individual.”
- Cancer (malignant tumour): “The malignant tumors… are a mass of proliferating cells called neoplastic or tumor cells… This property called metastasis is the most feared property of malignant tumors.”
- Addiction: “Addiction is a psychological attachment to certain effects… associated with drugs and alcohol.”
- Dependence: “Dependence is the tendency of the body to manifest a characteristic and unpleasant withdrawal syndrome if regular dose of drugs/alcohol is abruptly discontinued.”
(No formulas or SI units appear in the chapter.)
3. Important Diagrams and Activities
- Figure 7.1 – Stages in the life cycle of Plasmodium: demonstrates two-host (human + female Anopheles) cycle with sporozoites, liver/RBC stages and haemozoin release.
- Figure 7.2 – Inflammation in lower limb due to elephantiasis: shows chronic lymphatic blockage by Wuchereria.
- Figure 7.3 – Ringworm-affected area of skin: illustrates dry, scaly lesions caused by dermatophytes.
- Figure 7.4 – Structure of an antibody molecule: shows H₂L₂ arrangement (two heavy + two light chains) of Ig.
- Figure 7.5 – Diagrammatic representation of lymph nodes: shows primary (bone marrow, thymus) and secondary lymphoid organs.
- Figure 7.6 – Replication of retrovirus: illustrates HIV entry, reverse transcriptase, integration into host DNA and production in macrophages/T-cells.
- Figure 7.7–7.11 (Morphine, opium poppy, cannabinoid, Cannabis sativa, Datura): demonstrate sources and structures of common drugs of abuse.
4. Common Misconceptions and Exam Pitfalls
- Confusing innate (non-specific, at birth) with acquired (specific, memory-based) immunity or active (host produces antibodies) with passive (ready-made antibodies transferred).
- Mistaking vector for pathogen (female Anopheles is vector; Plasmodium is pathogen) or assuming all malaria is fatal (only P. falciparum causes malignant malaria).
- Thinking AIDS spreads by touch/contact (only via body fluids); overlooking that HIV infects macrophages first then helper T-cells.
- Assuming benign tumours spread (they remain localised); malignant tumours show metastasis.
- Believing vaccines give immediate protection (active immunity is slow; passive is used for quick response).
- Overlooking that drug abuse includes medicinal drugs taken without prescription or in excess.
5. Formula Sheet
No formulas, equations or numerical relationships are present in the chapter.