Human Health and DiseaseNEET Zoology · Class 12 · NCERT Chapter 7

Introduction

Human Health and Disease is one of the highest-yield chapters in NEET. Expect 3 to 4 questions every year. The chapter has five big sections: common diseases (pathogens), immunity, AIDS, cancer, and drugs of abuse. Most NEET questions are direct fact recall, so the goal here is to lock in the right facts cleanly.

I will keep facts NCERT-exact, group diseases by pathogen type (the way NEET tests them), and call out every common trap.

Common Diseases in Humans

NCERT groups human diseases by the type of pathogen. The categories you must know are: bacterial, viral, protozoan, fungal and helminthic. NEET asks pathogen-disease matching questions every year.

Bacterial Diseases

• Typhoid: caused by Salmonella typhi. Spread by contaminated food and water. Symptoms: sustained high fever, weakness, stomach pain, constipation, headache. Confirmed by the Widal test. Mary Mallon ("Typhoid Mary") was a famous carrier.
• Pneumonia: caused mainly by Streptococcus pneumoniae and Haemophilus influenzae. Infects alveoli, which fill with fluid. Symptoms: fever, chills, cough, headache. Severe cases turn the lips and finger nails grey to bluish.

Viral Diseases

• Common cold: caused by rhinoviruses. Infects the nose and upper respiratory tract (not lungs). Symptoms: nasal congestion, sore throat, cough, headache, tiredness. Spread by inhaled droplets and contaminated objects.

Protozoan Diseases

• Malaria: caused by Plasmodium (a protozoan). Four species infect humans: P. vivax, P. malariae, P. ovale, and P. falciparum (most lethal, causes malignant malaria). Transmitted by the bite of a female Anopheles mosquito.
• Amoebiasis (amoebic dysentery): caused by Entamoeba histolytica. Infects the large intestine. Spread by contaminated food and water; the housefly is the mechanical vector. Symptoms: constipation, abdominal pain, cramps, stools with mucus and blood.

Fungal and Helminthic Diseases

• Ringworm: a fungal infection caused by Microsporum, Trichophyton and Epidermophyton. Causes dry, scaly skin lesions (often in groin and between toes). Spread by contact with infected persons or fomites.
• Ascariasis: caused by the intestinal roundworm Ascaris lumbricoides. Symptoms: stomach pain, fever, anaemia, blockage of intestinal passage. Spread by ingestion of eggs in contaminated food and water.
• Filariasis (elephantiasis): caused by the filarial worms Wuchereria bancrofti and W. malayi. Transmitted by mosquito bite. Causes chronic blockage of lymphatic vessels, leading to gross swelling of the limbs (elephantiasis) and sometimes the genital organs.

Immunity

Immunity is the body's ability to fight pathogens. NCERT divides it into two main types: innate (present from birth, non-specific) and acquired (develops after exposure, specific).

Innate vs Acquired Immunity

The four barriers of innate immunity

1. Physical barriers: skin is the main barrier. Mucus coating the respiratory and digestive tracts traps microbes.
2. Physiological barriers: saliva in the mouth, hydrochloric acid in the stomach, tears (with lysozyme). They kill or destroy pathogens.
3. Cellular barriers: phagocytic cells like macrophages, neutrophils, monocytes; and natural killer (NK) cells. They engulf or destroy pathogens.
4. Cytokine barriers: virus-infected cells secrete interferons, which protect neighbouring cells from viral infection.

Two arms of acquired immunity

• Humoral (antibody-mediated) immunity: driven by B lymphocytes that produce antibodies into the blood and lymph.
• Cell-mediated immunity (CMI): driven by T lymphocytes that directly attack infected cells or activate other immune cells. Also responsible for graft rejection.

Both arms have memory: after the first exposure (primary response), the body remembers the pathogen. A second exposure (secondary response) produces a faster, stronger response. This is why vaccines work.

Active vs Passive Immunity

• Active immunity: your own body produces antibodies after exposure to antigen. Slow to develop, long lasting. Examples: recovering from chickenpox; BCG vaccination; hepatitis-B vaccine.
• Passive immunity: ready-made antibodies are transferred from outside. Acts fast, short lasting. Examples: a baby getting antibodies through the placenta (IgG) and through colostrum from the mother (IgA); tetanus antiserum injection; snake-bite antivenom.

Antibody Structure and Types

An antibody is a Y-shaped protein made by plasma cells (mature B cells). Each antibody molecule has the formula H₂L₂: two heavy (H) chains and two light (L) chains held together by disulphide bonds.

• The tip of the Y is the variable region; it is the part that binds the antigen and is called the paratope.
• The part of the antigen the antibody binds to is called the epitope.
• The base of the Y (constant region of the heavy chain) decides the isotype of the antibody (IgG, IgA, IgM, IgD or IgE).

Lymphoid Organs

Lymphoid organs are where lymphocytes mature, proliferate and interact with antigens. They are of two types:

• Primary lymphoid organs: bone marrow (where all lymphocytes originate; B cells mature here) and thymus (where T cells mature). The thymus is large in young children and shrinks with age.
• Secondary lymphoid organs: spleen (filters blood), lymph nodes (filter lymph), tonsils, Peyer's patches (in the small intestine), and MALT (mucosa-associated lymphoid tissue lining the respiratory, digestive and uro-genital tracts).

AIDS and HIV

AIDS (Acquired Immuno-Deficiency Syndrome) is caused by HIV, the Human Immunodeficiency Virus.

What is HIV?

• HIV is a retrovirus.
• Its genetic material is single-stranded RNA.
• It carries the enzyme reverse transcriptase, which makes a DNA copy from its RNA inside the host cell.
• It mainly infects helper T (CD4) cells and macrophages.

How HIV causes AIDS

1. HIV enters the body via infected fluids and infects a macrophage or CD4 T cell.
2. Reverse transcriptase copies the viral RNA into DNA. This viral DNA gets integrated into the host chromosome.
3. The infected cell starts producing new virus particles, which infect more T cells.
4. The CD4 T-cell count drops. The immune system collapses. The patient becomes vulnerable to ordinary infections (opportunistic infections), and is now in AIDS stage.

Transmission of HIV

HIV is spread by:

• Unprotected sexual contact with an infected person
• Transfusion of infected blood
• Sharing infected needles (especially drug users)
• Mother to fetus through the placenta (vertical transmission)

HIV is NOT spread by mosquito bites, hugging, sharing food, touching, sneezing, coughing, or living with an infected person. NEET tests this every other year.

Detection and treatment

HIV infection is confirmed by the ELISA (Enzyme-Linked Immunosorbent Assay) test, which detects anti-HIV antibodies. There is no cure. Antiretroviral drugs slow the disease but cannot eliminate the virus.

Cancer

Cancer is uncontrolled cell division. Normal cells have contact inhibition (they stop dividing when they touch other cells). Cancer cells have lost contact inhibition and divide uncontrolled.

Benign vs Malignant Tumours

• Benign tumour: stays in its original location. Does not spread. Usually not life-threatening unless it presses on a vital organ.
• Malignant tumour: grows rapidly and invades surrounding tissue. Cells can break off, travel through blood or lymph, and form new tumours at distant sites. This is metastasis, the dangerous property of cancer.

Carcinogens

Anything that causes cancer is a carcinogen. NCERT-tested examples:

• Physical: X-rays, gamma rays, UV rays
• Chemical: tobacco smoke, asbestos
• Biological: oncogenic viruses (HPV, hepatitis B)

Detection and treatment

• Detection: biopsy (gold standard, examines a tissue sample under microscope), imaging (X-ray, CT scan, MRI), blood tests for tumour markers, and antibody tests for cancer-specific antigens.
• Treatment: surgery (removes the tumour), radiotherapy (kills cancer cells with radiation), chemotherapy (kills cancer cells with drugs), and immunotherapy (uses interferonsto activate the body's immune response against the tumour).

Drugs and Alcohol Abuse

NCERT covers four classes of commonly abused drugs. Know the source plant and the main effect of each.

1. Opioids

Drugs that bind to opioid receptors in the gastrointestinal tract and central nervous system. Strong depressants and pain killers.

• Heroin (smack): chemically modified form of morphine. Obtained from the latex of the opium poppy (Papaver somniferum).
• Morphine: a powerful pain killer; medically useful but addictive.

2. Cannabinoids

From the cannabis plant (Cannabis sativa). Forms: marijuana, hashish, ganja and charas. Affect the cardiovascular system. Taken by inhalation or oral ingestion.

3. Cocaine

Obtained from the coca plant (Erythroxylum coca). A powerful stimulant of the central nervous system. Interferes with the transport of dopamine. Causes a sense of euphoria followed by hallucinations and increased aggression.

4. Tobacco and Alcohol

Tobacco contains nicotine, which stimulates the adrenal gland to release adrenaline and noradrenaline. Raises blood pressure and heart rate. Smoking causes lung cancer, oral cancer and bronchitis. Chewing tobacco causes oral cancer.

Alcohol depresses the central nervous system. Long-term abuse damages the liver (cirrhosis).

Worked NEET Problems

Summary Cheat Sheet

• Typhoid: Salmonella typhi; Widal test. Pneumonia: Streptococcus pneumoniae + Haemophilus influenzae. Common cold: rhinovirus.
• Malaria: Plasmodium (4 species; P. falciparum is most lethal); female Anopheles. Amoebiasis: Entamoeba histolytica; housefly carrier.
• Ringworm: Microsporum, Trichophyton, Epidermophyton (fungal). Ascariasis: Ascaris lumbricoides. Filariasis: Wuchereria bancrofti (mosquito-borne).
• Innate immunity: 4 barriers (physical, physiological, cellular, cytokine); non-specific, present from birth.
• Acquired immunity: 2 arms (humoral via B cells and antibodies; cell-mediated via T cells). Has memory.
• Active immunity: your own antibodies. Slow, long lasting (vaccines, infection).
• Passive immunity: ready-made antibodies. Fast, short lasting (colostrum, antiserum).
• Antibody: H₂L₂; tip of Y = variable region (paratope, binds antigen at the epitope).
• 5 antibodies (GAMED): IgG (most abundant, placenta), IgA (secretions), IgM (first in primary, pentamer), IgD (B-cell surface), IgE (allergy, parasites).
• Primary lymphoid organs: bone marrow + thymus. Secondary: spleen, lymph nodes, tonsils, Peyer's patches, MALT.
• HIV: retrovirus, RNA + reverse transcriptase, infects CD4 T cells. Detected by ELISA. NOT spread by casual contact or mosquito bite.
• Cancer: uncontrolled division, loss of contact inhibition. Malignant tumours metastasise.
• Cancer detection: biopsy is gold standard. Treatment: surgery, radio, chemo, immunotherapy (interferons).
• Drugs: heroin from Papaver somniferum; cannabinoids from Cannabis sativa; cocaine from Erythroxylum coca; nicotine from tobacco.

Next: use the interactive learning widgets to drill disease-pathogen matching, compare immunity types, and review antibody isotypes, or work through the 90+ NEET PYQs with full solutions. To time yourself, take the free 10-question mock test.