Human Health and Disease — NEET revision one-pager

01Chapter map & what health means

This chapter is almost pure recall — pathogen names, vectors, antibody types, karyotype-style facts. It reliably yields 3–4 NEET questions, and every one of them is winnable if the tables below are memorised cleanly. The losses here are never conceptual; they are name-swaps.

Definition to write verbatim

Health is a state of complete physical, mental and social well-being — not merely the absence of disease or infirmity. It is affected by genetic disorders, infections, lifestyle, food and water, rest and exercise, and personal hygiene.

Priority 1

Pathogen – disease – vector table (all 9 diseases)
Malaria life cycle and the stage that causes fever
Innate vs acquired immunity; the four innate barriers
Antibody structure and the five classes

Priority 2

Primary vs secondary immune response
AIDS: HIV replication, ELISA, transmission
Cancer: metastasis, oncogenes, detection, treatment
Drugs and alcohol abuse; adolescence

02Common infectious diseases

Disease	Pathogen	Type	Transmission	Symptoms & notes
Typhoid	Salmonella typhi	bacterium	contaminated food and water	Sustained high fever 39–40°C, weakness, stomach pain, constipation, headache, loss of appetite; intestinal perforation in severe cases. Confirmed by the Widal test. Mary Mallon (Typhoid Mary) was a cook who spread it through the food she prepared.
Pneumonia	Streptococcus pneumoniae, Haemophilus influenzae	bacterium	droplets/aerosols; sharing utensils	Alveoli fill with fluid → severe breathing problems; fever, chills, cough, headache; lips and finger nails turn grey to bluish.
Common cold	Rhinoviruses	virus	droplets, contaminated objects	Infects nose and respiratory passage but not the lungs. Nasal congestion and discharge, sore throat, hoarseness, cough, headache, tiredness; lasts 3–7 days.
Malaria	Plasmodium vivax, P. falciparum, P. malariae	protozoan	bite of female Anopheles	Chill and high recurring fever every 3–4 days. Malignant malaria is caused by P. falciparum and can be fatal.
Amoebiasis (amoebic dysentery)	Entamoeba histolytica	protozoan	contaminated food and water; housefly is the mechanical carrier	Lives in the large intestine; constipation, abdominal pain and cramps, stools with excess mucous and blood clots.
Ascariasis	Ascaris lumbricoides	helminth (roundworm)	contaminated water, vegetables, fruits, soil	Internal bleeding, muscular pain, fever, anaemia, blockage of the intestinal passage.
Filariasis (elephantiasis)	Wuchereria bancrofti, W. malayi	helminth (filarial worm)	bite of a female *Culex* mosquito	Chronic inflammation of the lymphatic vessels of the lower limbs; the genital organs are also often affected. Deformity appears after years.
Ringworm	Microsporum, Trichophyton, Epidermophyton	fungus	soil, contaminated towels, clothes, combs	Dry, scaly lesions with intense itching on skin, nails and scalp; heat and moisture help the fungus grow.

Pathogen quick-fire tap a disease to check yourself

The name-swaps that cost marks

Anopheles carries malaria; Culex carries filariasis; Aedes carries dengue and chikungunya.
Housefly is the mechanical carrier of amoebiasis — it does not host a life-cycle stage, unlike the mosquito in malaria.
The common cold does not reach the lungs. Pneumonia is the one that fills the alveoli.

03Life cycle of Plasmodium

Two hosts. Humans are the secondary (intermediate) host where asexual multiplication occurs; the female Anopheles mosquito is the primary (definitive) host where the sexual phase is completed.

The fever is caused by haemozoin, released when infected red blood cells rupture — not by the parasite entering the cell.

Three lines that answer most malaria questions

The infective stage to humans is the sporozoite; the stage infective to the mosquito is the gametocyte.
Sexual reproduction happens in the mosquito, which is why the mosquito is the primary host even though we call it the vector.
Only the female Anopheles bites for blood — she needs it for egg development.

04Immunity — innate and acquired

Innate immunity (non-specific, present from birth) — four barriers

Barrier	Components
Physical	Skin; mucus coating of the epithelium lining the respiratory, gastrointestinal and urogenital tracts
Physiological	Acid in the stomach, saliva in the mouth, tears from the eyes
Cellular	Polymorphonuclear leucocytes (neutrophils), monocytes, natural killer lymphocytes in blood; macrophages in tissues
Cytokine	Virus-infected cells secrete interferons which protect the neighbouring uninfected cells

Acquired immunity (specific, has memory)

Pathogen-specific and characterised by memory. The first encounter gives a primary response of low intensity; a later encounter with the same pathogen gives a much faster, much stronger secondary (anamnestic) response.
Carried out by two kinds of lymphocyte. B-lymphocytes produce an army of proteins — antibodies — giving humoral (antibody-mediated) immunity. T-lymphocytes do not make antibodies but help B cells and attack infected cells, giving cell-mediated immunity (CMI). CMI is what rejects a transplanted graft, and it is why the body can tell self from non-self.

Live: primary vs secondary antibody response slide through the days

Day after first exposure

Second exposure on day

Antibody structure

Every antibody is H₂L₂: two identical heavy chains and two identical light chains, with two antigen-binding sites.

Class	Where / when
IgG	Most abundant; the only class that crosses the placenta — natural passive immunity to the foetus
IgA	Secretions — saliva, tears, mucus and especially colostrum, the first milk
IgM	Largest; the first antibody made in a primary response
IgE	Mediates allergy; binds mast cells and basophils
IgD	Receptor on the surface of B-lymphocytes

Active vs passive immunity

	Active	Passive
How	The body makes its own antibodies after exposure to a live or dead antigen	Ready-made antibodies are given directly
Speed	Slow — takes time to build up	Immediate
Memory	Yes, long lasting	No, short lived
Examples	Natural infection; vaccination	Mother's antibodies across the placenta (IgG) and in colostrum (IgA); anti-tetanus and anti-venom serum

Lymphoid organs

Primary (where lymphocytes mature and become immunocompetent): bone marrow and thymus.
Secondary (where they meet the antigen and proliferate): spleen, lymph nodes, tonsils, Peyer's patches of the small intestine, appendix.
The spleen is a large bean-shaped organ full of lymphocytes and phagocytes; it filters trapped microorganisms from the blood and is a reservoir of erythrocytes.
MALT (mucosa-associated lymphoid tissue) makes up about 50% of the lymphoid tissue in the human body.
The thymus is large at birth and shrinks steadily with age.

Vaccination, allergy, autoimmunity

Vaccination introduces an inactivated or weakened pathogen (or its antigenic proteins) so the body forms antibodies and, more importantly, memory B and T cells. If preformed antibodies are injected instead, that is passive immunisation — used for snake bite and tetanus, where there is no time to wait.
Allergy: exaggerated response to environmental antigens (mites, pollen, animal dander). IgE antibodies are produced; mast cells release histamine and serotonin, giving sneezing, watery eyes, running nose, difficulty in breathing. Treated with anti-histamines, adrenaline and steroids.
Autoimmunity: the immune system attacks self cells. Rheumatoid arthritis is the standard example.

05AIDS — Acquired Immuno Deficiency Syndrome

Caused by the Human Immunodeficiency Virus (HIV), a retrovirus — it has RNA and an envelope, and reverse transcribes its genome into DNA. First reported in 1981.

Transmission

Sexual contact with an infected person.
Transfusion of contaminated blood; sharing infected needles (a major route among drug abusers).
From an infected mother to her child through the placenta.
Not spread by touching, shaking hands, hugging, sharing food, or insect bites. There is no risk in ordinary social contact.

Replication — the sequence to write in order

Diagnosis is by ELISA. Treatment uses anti-retroviral drugs (AZT) — only partly effective; it delays death but does not cure.

Prevention — NACO points

Make blood from licensed blood banks safe from HIV, use disposable needles and syringes, distribute free condoms, control drug abuse, advocate safe sex, and promote regular check-ups. HIV/AIDS-infected people need help and sympathy, not isolation — that line is asked directly.

06Cancer

In a normal cell, growth and differentiation are strictly regulated. Cancer cells have lost contact inhibition — the property by which contact with other cells stops uncontrolled growth — so they divide continuously and pile up into a mass of cells called a tumour.

	Benign tumour	Malignant tumour
Growth	Confined to its original site	Rapidly growing mass that invades and damages surrounding tissue
Spread	Does not spread	Metastasis — cells break away, travel in the blood and start new tumours elsewhere
Effect	Little damage	Starves the normal cells by competing for nutrients; usually fatal if untreated

Causes

Physical carcinogens: ionising radiations — X-rays, gamma rays; non-ionising — UV.
Chemical carcinogens: tobacco smoke is the biggest single one, responsible for a large share of lung and throat cancers.
Biological: oncogenic viruses carry viral oncogenes. Normal cells carry proto-oncogenes (cellular oncogenes, c-onc) which, when activated under certain conditions, transform the cell into a cancerous one.

Detection and treatment

Biopsy and histopathological studies of the tissue; blood and bone marrow tests for leukaemias.
Radiography (X-rays), CT scan, MRI — CT uses X-rays to build a three-dimensional image; MRI uses strong magnetic fields and non-ionising radiation.
Monoclonal antibodies against cancer-specific antigens detect certain cancers; techniques of molecular biology can find genes that make a person susceptible.
Treatment: surgery, radiotherapy (tumour cells are irradiated lethally while normal tissue is protected) and chemotherapy (drugs, most with side effects such as hair loss and anaemia). Most cancers are treated with a combination. α-interferon is given as a biological response modifier — it activates the patient's own immune system.

Two-word answers that get asked

Loss of contact inhibition → uncontrolled division. Metastasis → the property that makes a tumour malignant. Proto-oncogene → the normal gene; oncogene → the activated cancer-causing form.

07Drugs and alcohol abuse

Group	Source	Drug	Action
Opioids	Papaver somniferum (poppy) latex	Morphine; heroin (smack) = diacetylmorphine, a white, odourless, bitter crystalline compound obtained by acetylation of morphine	Bind opioid receptors in the central nervous system and gut; depressant, slows body functions. Morphine is a very effective sedative and painkiller, used after surgery.
Cannabinoids	Cannabis sativa — inflorescences, resin, leaves	Marijuana, hashish, charas, ganja	Interact with cannabinoid receptors present principally in the brain; affect the cardiovascular system. Also abused by some sportspersons.
Coca alkaloid	Erythroxylum coca	Cocaine, coke, crack	Interferes with the transport of the neurotransmitter dopamine; a potent stimulant of the CNS, giving euphoria and increased energy, then hallucinations.
Other hallucinogens	plants	from Atropa belladonna and Datura	hallucinogenic
Tobacco	Nicotiana tabacum	Nicotine	Stimulates the adrenal medulla to release adrenaline and nor-adrenaline → raised blood pressure and heart rate. Linked to cancers of lung, urinary bladder and throat, bronchitis, emphysema, coronary heart disease, gastric ulcer. Smoking raises carbon monoxide in blood and lowers the oxygen-carrying haemoglobin.

Why adolescents, and what to watch for

Adolescence is the period between 12 and 18–19 years — a bridge between childhood and adulthood, with major biological and psychological change. It is a vulnerable phase.
Common causes: curiosity, adventure and excitement, the desire to do something new, peer pressure, academic or examination stress, unstable family structures, and media and film glamorisation.
Warning signs: drop in academic performance, unexplained absence from school, poor personal hygiene, withdrawal and isolation, depression, fatigue, aggressive and rebellious behaviour, deteriorating relationships, change in sleeping and eating habits, fluctuating weight and appetite.
Addiction is a psychological attachment to the effects of a drug. Dependence is the body adapting so that it functions normally only in the drug's presence; withdrawal then produces anxiety, shakiness, nausea and sweating.
Prevention and control: avoid undue peer pressure, educate and counsel to face problems and stress, seek help from parents and peers, look for professional and medical help, and use the help of de-addiction and rehabilitation programmes.

Long-term consequences

Damage to the nervous system and liver cirrhosis from alcohol; in pregnant women, harm to the growing foetus. Intravenous drug use with shared needles is a major route for AIDS and hepatitis B. Anabolic steroid misuse causes acne, aggression, and in females masculinisation, menstrual irregularity, deepening of voice, and in males reduced sperm production and enlargement of the prostate.

08Last-hour recall sheet & rapid drill

Prompt	Answer
Widal test	typhoid (Salmonella typhi)
ELISA	AIDS (HIV)
Haemozoin	toxin released when infected RBCs rupture → chill and fever in malaria
Infective stage to human / to mosquito	sporozoite / gametocyte
Antibody in colostrum	IgA (passive immunity to the newborn)
Antibody crossing the placenta	IgG
Antibody of allergy	IgE; mast cells release histamine and serotonin
Primary lymphoid organs	bone marrow and thymus
Interferons	cytokine barrier of innate immunity, from virus-infected cells
Graft rejection	cell-mediated immunity (T-lymphocytes)
Property lost by cancer cells	contact inhibition
Spread of malignant tumours	metastasis
Source of heroin / cocaine / marijuana	Papaver somniferum / Erythroxylum coca / Cannabis sativa
Nicotine acts on	adrenal medulla → adrenaline and nor-adrenaline

Rapid drill — 10 one-liners tap to reveal

Final checklist

Vector questions: Anopheles = malaria, Culex = filariasis, housefly = amoebiasis (mechanical only).
Antibody questions: match the class to the place (colostrum, placenta, allergy, B-cell surface, first response).
Immunity questions: ask first whether it has memory. Memory ⇒ acquired; no memory ⇒ innate.
Assertion–reason on immunity is a recurring loss — check whether the reason is a true statement and the correct explanation.
Do not confuse the primary lymphoid organs (maturation) with the secondary ones (antigen encounter).