Human Health And Diseases: Complete Class 12 NEET Zoology Revision Notes by PW

Keeping track of diseases, their causes, symptoms, prevention, and different types of immunity can make Human Health and Diseases difficult to revise for NEET. With several closely related concepts and NCERT details to remember, you need clear explanations and regular revision to build a strong grasp of the chapter. 

The Human Health and Diseases Class 12 NEET Zoology One- Shot by Physics Wallah covers the important concepts from the chapter in a way that supports focused revision. You can use it to strengthen your understanding of human health, diseases, immunity and related topics while preparing for NEET.

What do Health and Immunity mean?

Understanding the difference between health and immunity helps you connect the basic concepts of the chapter. While health refers to overall well-being, immunity focuses on how the body protects itself from infections and diseases. 

 Health includes:

• Mental Well-Being

• Physical Well-Being

• Emotional Well-Being

The immune system protects the body against disease. Immunity is the body’s mechanism of defence and is classified into innate immunity and adaptive immunity.

 Components Of Innate Immunity

Innate immunity has four major components:

1. Physical Barriers: Skin, mucous membranes, nasal hair, and respiratory cilia prevent pathogen entry.

2. Physiological Barriers: HCl in the stomach and lysozyme in saliva and tears destroy microorganisms. Vaginal acidity also prevents infection. Lysozyme mainly acts against bacteria, not viruses.

3. Cellular Barriers: Monocytes, macrophages, neutrophils, and natural killer cells destroy pathogens or infected cells. Monocytes become macrophages after entering tissues.

4. Cytokine Barriers: Virus-infected cells release interferons, which protect nearby cells from viral infection.

Features Of Adaptive Immunity

Adaptive immunity shows:

• Specificity: Different pathogens produce different antibodies.

• Diversity: The body can produce many types of antibodies.

• Self–Non-Self Discrimination: Immune cells identify foreign cells.

• Memory: Memory cells create a faster response during later exposure.

MHC molecules act as identifying markers on body cells. Different MHC types help the immune system recognise transplanted cells as foreign.

Immune Response And Lymphocytes

The first exposure produces a slow and weaker primary response. A later exposure produces a rapid and stronger secondary or anamnestic response because of memory cells. IgM appears first during the primary response, while IgG is produced prominently during the secondary response.

• B Cells: Produce antibodies and provide Humoral-Mediated Immunity (HMI) against pathogens in body fluids.

• T Cells: Provide Cell-Mediated Immunity (CMI) against pathogens inside cells.

• Helper T Cells: Support B cells and cytotoxic T cells.

• Cytotoxic T Cells: Destroy infected or foreign cells.

A cytotoxic T cell releases perforin, which forms pores in the membrane of an infected cell. This also explains graft rejection when transplanted tissue has a different MHC type.

Antibodies And Antigens

Antibodies are proteins called immunoglobulins or gamma globulins. Each antibody contains:

• Two heavy chains

• Two light chains

• Disulfide bridges

• A variable antigen-binding region

• A constant region

The antibody structure is represented as H₂L₂. An antigen is a molecule that stimulates antibody production. Antibodies bind to specific surface points called epitopes.

The five antibody isotypes are IgG, IgA, IgM, IgE, and IgD.

• IgG: Smallest antibody; crosses the placenta and can act as an antitoxin.

• IgA: Secretory antibody present in saliva, colostrum, and breast milk.

• IgM: Largest antibody; consists of five units and causes rapid agglutination.

• IgE: Associated with allergy and present on mast cells and eosinophils.

• IgD: Membrane-bound receptor on B cells.

Antibodies do not directly kill bacteria. They bind pathogens, reduce their movement, cause agglutination, and help phagocytes engulf them.

Active And Passive Immunity

Active immunity develops after infection or vaccination. Passive immunity includes maternal IgG crossing the placenta, IgA received through breast milk, and antiserum given after snake bites or injuries.

Vaccines

Edward Jenner developed the first vaccine against smallpox and is regarded as the father of immunology. A vaccine introduces weakened, killed, or selected components of a pathogen. It activates B cells, produces antibodies, and forms memory cells. A vaccine acts like a practice exercise for the immune system.

Modern vaccines may contain:

• Weakened or inactivated pathogens

• Selected antigenic fragments

• Recombinant proteins produced by organisms such as yeast

Recombinant vaccines are made by inserting the gene for a pathogen’s antigen into a host organism, which produces the required protein.

Allergy And Autoimmunity

An allergy is an excessive immune response to a normally harmless substance called an allergen. Dust, pollen, mites, animal dander, and certain metals may cause allergy.

Symptoms include sneezing, itching, watery eyes, skin redness, breathing difficulty, and wheezing.

• Hay Fever: Affects the upper respiratory tract.

• Eczema: Affects the skin.

• Asthma: Affects the lower respiratory tract.

Allergens bind to IgE on mast cells and eosinophils. These cells release histamine, causing blood-vessel dilation. Excessive histamine release can cause anaphylactic shock, severe blood-pressure reduction, and possible death. Antihistamines, adrenaline, and immunosuppressive drugs may be used.

Autoimmunity occurs when the immune system attacks the body’s own cells. Rheumatoid arthritis is an example in which immune reactions may affect synovial fluid and joints.

Lymphoid Organs

Primary Lymphoid Organs

• Bone Marrow: Origin of all lymphocytes and maturation site of B cells.

• Thymus: Maturation site of T cells; it is large in childhood and reduces after puberty.

Secondary Lymphoid Organs

These are sites where mature lymphocytes meet antigens and form effector cells.

• Spleen: Filters blood and detects blood-borne pathogens.

• Lymph Nodes: Filter tissue fluid.

• Tonsils: Monitor pathogens entering through the mouth.

• Peyer’s Patches: Present in the ileum.

• MALT: Protects mucosal surfaces.

• Appendix: Associated with lymphoid tissue.

AIDS And Cancer

AIDS

AIDS means Acquired Immunodeficiency Syndrome. It is caused by HIV, an RNA-containing retrovirus. HIV uses the GP120 glycoprotein to bind to the CD4 receptor on macrophages and helper T cells.

Memory Tip: GP120 is the key, CD4 is the lock, and the macrophage is the factory of HIV.

HIV converts RNA into DNA using reverse transcriptase. The viral DNA integrates with host DNA and produces new virus particles. Destruction of helper T cells weakens both humoral and cell-mediated immunity.

Transmission occurs through:

• Unprotected sexual contact

• Contaminated needles

• Infected blood transfusion

• Infected mother to child

HIV is not spread by hugging, dry kissing, sharing food, or mosquito bites. ELISA is used as a preliminary test, while PCR provides confirmation. AZT inhibits reverse transcription.

Cancer

Cancer is uncontrolled cell division. A tumour may be benign or malignant. Malignant tumours spread through blood by metastasis.

Cancer cells show:

• Loss of contact inhibition

• Uncontrolled proliferation

• Immature and undifferentiated structure

Cancer may involve activated proto-oncogenes and inactive tumour-suppressor genes. Carcinogens include radiation, tobacco, asbestos, pollutants, and oncogenic viruses.

Diagnosis may involve biopsy, histopathology, CT scan, MRI, and bone-marrow examination. Treatment includes surgery, radiation, chemotherapy, and immunotherapy.

• Carcinoma: Cancer of epithelial tissue

• Leukaemia: Blood cancer

• Sarcoma: Cancer of muscle, bone, or other mesodermal tissue

Memory Tip: Carcinoma means epithelial lining, leukaemia means blood, and sarcoma means muscle or bone.

Important Infectious Diseases

In malaria, sporozoites enter humans through a mosquito bite and first reach the liver. They later enter red blood cells and consume haemoglobin. Rupture of infected red blood cells releases hemozoin, causing chills and recurring fever. F for falciparum, F for fatal: P. falciparum may cause cerebral malaria.

Drug Abuse

Drug abuse means using medicines or chemicals for non-medical purposes or in excessive amounts.

• Opioids: Obtained from Papaver somniferum. Morphine is a painkiller and depressant. Heroin, or smack, is more dangerous.

• Cannabinoids: Obtained from Cannabis sativa. Products include ganja, charas, hashish, marijuana, and bhang.

• Cocaine: Obtained from Erythroxylum coca. It is a stimulant that increases alertness, energy, and euphoria.

• LSD: Obtained from Claviceps purpurea and may cause hallucinations.

• Benzodiazepines And Barbiturates: Sedatives that slow body functions.

• Amphetamines: Stimulants that increase activity and may be misused in sports.

Revise Human Health and Diseases with PW to strengthen your understanding of important disease, immunity and health-related concepts.

Combine concept revision with NCERT-based practice and NEET questions to check how well you can apply what you have learned. 

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