Human Health and Diseases Class 12 Notes Biology Chapter 8 - CBSE


What are Human Health and Diseases?

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    Health is the state of complete physical, mental, and social well-being.


    A condition of the living body or plant or one of its parts that impairs normal functioning and is typically manifested by distinguishing signs and symptoms : like sickness, malady etc.



    ➥ Communicable or infectious diseases
    • Viral diseases (common cold, chikungunya & dengue)
    • Bacterial diseases (typhoid, pneumonia, diphtheria & plague)
    • Protozoal diseases (amoebiasis & malaria)
    • Helminthic diseases (ascariasis & filariasis)
    • Fungal diseases (ring worm)


    ➥ Non-Communicable or non-infectious diseases
    • Allergies
    • Cancer

    Pathogenic Diseases

    Pathogens also known as infectious agents are the parasites that enter the human body through various means, then multiply, and interfere with normal metabolic activities of the host. They are organisms that can cause disease. There are five main types of Pathogens :

    • Bacteria
    • Viruses
    • Fungi
    • Protists
    • Parasitic Worms

    Controlling The Spread Of Pathogenic Disease

    • Keeping up to date with recommended vaccines.
    • Keeping surfaces clean
    • Cleaning kitchen and bathrooms
    • Cells
    • Staying home when ill
    • Avoid insects bites
    • Practicing safe sex


    • A branch of biology covering study of immune systems in all organisms.
    • Pistil (Female Reproductive Part) consist of: Stigma, Style, Ovary.


    • The ability of body to fight the disease-causing organisms is called immunity. In other words it is the state of protection from infectious disease.


    Adaptive Immunity

    ➥ Natural

    • Passive (Maternal)
    • Active (Infection)

    Innate Immunity

    ➥ Artificial

    • Passive (Antibody Transfer)
    • Active (Immunization)

    Innate Immunity

    • ➥ Physical Barriers
    • ➥ Physiological Barriers
    • ➥ Cellular Barriers
    • ➥ Cytokine Barriers

    Acquired Immunity

    • It is acquired, which means that it is produced in response to a second encounter with a pathogen. It is based on memory and is pathogen specific.
    • When a pathogen for the first time infects a person, low intensity immune response is generated (primary response).
    • Self-incompatibility.
    • When the same pathogen attacks again, intensified immune response in generated (secondary response).
    • Acquired immunity involves two types of cells − B-lymphocytes and T- lymphocytes.


    Vaccination is the term used for giving a vaccine i.e., the process of introducing a substance to a host.


    Immunisation is the term used for the process of both getting the vaccine and becoming immune to the disease as a result of the vaccine.

    Organs Of Human Immune System

    Lymphoid Organs

    ➥ Primary Lymphoid Organ ➥ Secondary Lymphoid Organ
    ➥ It consist of bone marrow and thymus. ➥ Lymphocytes migrate here after attaining maturity.

    Aids (Acquired Immuno Deficiency Syndrome)

    It is caused by HIV (Human Immunodeficiency Virus) [HIV is a retrovirus (RNA virus)].

    Transmission of HIV occurs through:

    Sexual contact with infected person, Sharing infected needles, Transfusion of contaminated Infected blood from mother to child through placenta.

    Diagnosis of AIDS

    By ELISA (Enzyme Linked Immuno Sorbent Assay)


    No permanent cure; antiretroviral therapies can prolong the life of patient.

    Prevention of AIDS

    • Ensuring use of disposable syringes, screening blood from blood banks, Advocating safe sex
    • NACO (National AIDS Control Organization) and many NGOs are creating a lot of awareness among people.


    • The process of development of cancer is called oncogenic transformation.
    • Normal cells have the property of contact inhibition (stoppage of growth on coming in contact with other cells), but cancer cells lose this property.

    Types Of Tumor

    Benign Tumors

    Remain confined to their original location and do not spread.

    Malignant Tumors

    These exhibit metastasis i.e., the cells sloughed from such tumors reach distant sites and wherever they reach, new tumor is formed.

    Diagnosing Cancer

    • ➥ Biopsy
    • ➥ Radiography
    • ➥ CT Scan
    • ➥ MRI Scan

    Treatment of Cancer

    • ➥ Radiotherapy
    • ➥ Chemotherapy
    • ➥ Immunotherapy

    Types of Drugs

    • ➥ Opioids (Heroin)
    • ➥ Cannabinoids
    • ➥ Cocaine
    • ➥ Nicotine

    Alcohol/drug Uses

    • Alcohol / drug abuse normally starts in adolescence (period between 12-18 yrs. − transition phase between childhood and adulthood).
    • When a person uses alcohol/ drug on regular basis, he becomes addicted.
    • Withdrawal syndrome − Anxiety, nausea, sweating, shakiness, and sometimes may be fatal.
    • Excess alcohol causes damage to liver (cirrhosis) nervous system.