Chapter Notes: Human Health and Diseases

Table of Contents
1. Introduction
2. Components of Health
3. Maintaining Good Health
4. Infectious and Non-infectious Diseases
5. Common Diseases in Humans
6. Prevention and Control of Infectious Diseases
7. Advancements in Biological Science
8. Immunity
9. Vaccination and Immunisation
10. Allergies
11. Autoimmunity
12. Immune System in the Body
13. AIDS
14. Cancer
15. Drugs and Alcohol Abuse
16. Adolescence and Drug/Alcohol Abuse
17. Prevention and Control
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NEET  2026 Guidance: 13 questions were asked in last 2 years and 28 questions were asked in last 5 years.

Introduction

• Health is not merely the absence of disease or physical fitness; it is a state of complete physical, mental, and social well-being.
• Good health enhances work efficiency, leading to increased productivity and economic prosperity; it also contributes to greater longevity and reduces infant and maternal mortality.

Components of Health

• Genetic disorders: Conditions present at birth or inherited from parents (examples: cystic fibrosis, hemophilia).
• Infections: Diseases caused by pathogenic organisms such as bacteria, viruses, fungi, protozoa, or helminths (examples: influenza, tuberculosis, malaria).
• Lifestyle factors: Diet, quality of drinking water, rest, exercise and habits like smoking or excessive alcohol use that influence health.

Maintaining Good Health

• Balanced diet: Adequate proportions of carbohydrates, proteins, fats, vitamins and minerals to meet physiological needs.
• Personal hygiene: Regular handwashing, dental care and bathing to reduce infection risk.
• Regular exercise: Physical activities such as walking, running, yoga or sports to maintain fitness.
• Yoga: Practice of physical postures, breathing exercises and meditation to promote physical and mental well-being.
• Awareness and prevention: Knowledge of diseases and preventive measures such as vaccination, safe waste disposal and food/water hygiene.

Infectious and Non-infectious Diseases

• Diseases are broadly classified as infectious (transmissible between individuals) and non-infectious (not transmitted person-to-person).
• Infectious diseases: Caused by pathogens and spread by direct contact, droplets, vectors or contaminated food/water (examples: common cold, influenza, tuberculosis, HIV/AIDS).
• Non-infectious diseases: Result from genetic, lifestyle or environmental factors (examples: cancer, heart disease, diabetes).

Common Diseases in Humans

Organisms that cause disease are called pathogens. Pathogens include bacteria, viruses, fungi, protozoans and helminths. They enter the body by various routes, multiply and disrupt normal functions. Pathogens must adapt to conditions within the host, for example, surviving acidic stomach conditions if they enter via the gut.

1. Typhoid

• Cause: The bacterium Salmonella typhi, usually transmitted by contaminated food and water.
• Symptoms: Sustained high fever (39-40°C), weakness, abdominal pain, constipation, headache and loss of appetite.
• Severe cases may lead to intestinal perforation and death.
• Diagnosis can include the Widal test.
• Historical note: Mary Mallon (known as Typhoid Mary) was a cook who unknowingly spread typhoid by contaminating food.

2. Pneumonia

• Causes: Common bacterial agents include Streptococcus pneumoniae and Haemophilus influenzae.
• Pathology: Infection of the alveoli (air sacs) causes them to fill with fluid or pus, impairing gas exchange and causing respiratory distress.

• Symptoms: Fever, chills, cough and headache; in severe cases lips and fingertips may appear grey or bluish from inadequate oxygenation.
• Transmission: Spread by inhalation of infected droplets; shared utensils or close contact can transmit the causative agents.
• Other important bacterial diseases: Dysentery, plague, diphtheria.

3. Common Cold

• Cause: Primarily rhinoviruses, affecting the nose and upper respiratory passages but not usually the lungs.
• Symptoms: Nasal congestion and discharge, sore throat, hoarseness, cough, headache and tiredness; typically last 3-7 days.
• Transmission: Spread by respiratory droplets and by contact with contaminated objects (pens, cups, doorknobs, keyboards).

4. Malaria

• Cause: Protozoan parasites of the genus Plasmodium.
• Species of medical importance: P. vivax, P. malariae, P. falciparum (the latter causes the most severe, potentially fatal malaria).

Life cycle of Plasmodium (summary)

• Entry into human: Infective sporozoites enter when an infected female Anopheles mosquito bites.
• Multiplication in liver: Sporozoites invade and multiply within liver cells.
• Blood infection: Parasites enter and multiply within red blood cells (RBCs), causing rupture of RBCs.
• Symptoms: Rupture releases toxic pigment haemozoin, causing chills and high fever at periodic intervals (every 48-72 hours depending on species).
• Transmission to mosquito: When a mosquito bites an infected person, it ingests sexual stages that develop and multiply within the mosquito to produce sporozoites stored in salivary glands.
• Cycle continues: Subsequent mosquito bites transmit sporozoites to new human hosts.

Life Cycle of Plasmodium

Note: The malarial parasite requires two hosts - humans and female Anopheles mosquitoes; the mosquito serves as both vector and definitive host for sexual stages.

5. Amoebiasis (Amoebic Dysentery)

• Cause: The protozoan Entamoeba histolytica residing in the large intestine.
• Symptoms: Abdominal pain and cramps, constipation or loose stools containing excess mucus and blood clots.
• Transmission: Faecal-oral route; houseflies can mechanically transfer cysts from faeces to food. Contaminated food and water are the main sources of infection.

6. Ascariasis

• Cause: The roundworm Ascaris lumbricoides.
• Symptoms: Internal bleeding, muscular pain, fever, anaemia and intestinal blockage in severe infections.
• Transmission: Eggs excreted in faeces contaminate soil; ingestion of contaminated water, vegetables or fruits infects new hosts.

7. Elephantiasis (Filariasis)

Elephantiasis

• Cause: Filarial worms such as Wuchereria bancrofti and W. malayi.
• Pathology: Chronic infection causes inflammation and obstruction of lymphatic vessels, leading to severe swelling of limbs and sometimes genital deformities.
• Transmission: Spread by bites of infected female mosquitoes.

8. Fungal Infections

Ringworm affected area of the skin

Superficial fungal infections such as ringworm are caused by dermatophytes from genera Microsporum, Trichophyton and Epidermophyton. These fungi prefer warm, moist areas such as skin folds.

• Sources: Contaminated soil and personal items (towels, clothes, combs) can spread infection.
• Symptoms: Dry, scaly lesions on skin, nails or scalp together with intense itching.

Prevention and Control of Infectious Diseases

Personal Hygiene

• Body cleanliness: Regular bathing and handwashing to reduce the load of infectious agents.
• Safe consumption: Use of clean drinking water and properly washed/cooked food, fruits and vegetables.

Public Hygiene

• Waste disposal: Proper removal and treatment of waste and excreta to prevent environmental contamination.
• Water reservoirs: Regular cleaning and disinfection of tanks, pools and ditches.
• Public catering: Observance of hygiene standards in food preparation and serving.

Prevention of Air-borne Diseases

Avoid close contact with infected persons; isolate infected individuals where appropriate and avoid sharing personal items that may be contaminated.

Prevention of Insect-borne Diseases

• Vector control: Eliminate mosquito breeding sites (stagnant water), clean household coolers, use mosquito nets and screens.
• Biological control: Introducing fish like Gambusia in ponds to feed on larvae.
• Chemical control: Spraying appropriate insecticides in ditches and swamps.
• Physical barriers: Wire mesh on doors and windows to prevent mosquito entry.

Advancements in Biological Science

• Vaccines and immunisation: Vaccination has eradicated diseases like smallpox and controlled others such as polio, diphtheria, pneumonia and tetanus.
• Biotechnology: Development of newer and safer vaccines and diagnostic tools using molecular and recombinant methods.
• Antibiotics and drugs: Discovery of antibiotics and other therapeutic agents has improved treatment of many infectious diseases.

Immunity

Immunity is the ability of the body to resist and eliminate infectious agents. Two broad types of immunity are recognised: innate (natural) immunity and acquired (adaptive) immunity.

Innate Immunity

Innate immunity is non-specific and present at birth. It consists of barriers that prevent pathogen entry and early cellular responses.

• Physical barriers: Skin and mucus linings of the respiratory, gastrointestinal and urogenital tracts trap or block microbes.
• Physiological barriers: Stomach acid, saliva and tears contain substances that inhibit microbes.
• Cellular barriers: Phagocytic cells such as neutrophils, monocytes (macrophages) and natural killer (NK) cells engulf and destroy microbes.
• Cytokine barriers: Interferons secreted by virus-infected cells help protect neighbouring cells from viral replication.

Acquired (Adaptive) Immunity

Acquired immunity is specific to particular pathogens and shows memory. The first encounter with an antigen produces a primary response; subsequent encounters produce a stronger secondary (anamnestic) response due to memory cells.

Key Cells: B-lymphocytes and T-lymphocytes

• B-lymphocytes: Differentiate into plasma cells that produce antibodies (immunoglobulins).
• T-lymphocytes: Include helper T cells that assist B cells and cytotoxic T cells that kill infected cells; T cells mediate cell-mediated immunity and do not secrete antibodies themselves.

Antibody Structure

Structure of an Antibody

Antibodies are proteins composed of two identical heavy chains and two identical light chains, often written as H2L2. The variable regions bind specific antigens.

Types of Antibodies

Major classes include IgA, IgM, IgE and IgG. Antibody-mediated responses circulating in body fluids are referred to as the humoral immune response.

Types of Acquired Immune Response

• Antibody-mediated (humoral) response: Involves B-cells and antibodies to neutralise extracellular pathogens.
• Cell-mediated immune response (CMI): Mediated by T-cells to eliminate infected or abnormal cells without using antibodies.

Importance of Tissue and Blood Group Matching in Transplants

• Tissue matching: Human leukocyte antigen (HLA) compatibility reduces graft rejection.
• Blood group matching: ABO compatibility is essential for safe transplantation.
• Even with matching, recipients frequently require lifelong immunosuppressants to prevent rejection because the immune system distinguishes 'self' from 'non-self' and may mount a cell-mediated response against grafts.

Active and Passive Immunity

When a host produces its own antibodies after exposure to antigens (natural infection or vaccination), this is active immunity - it develops slowly but is long-lasting. Passive immunity is the immediate protection provided by transfer of preformed antibodies (e.g. maternal antibodies through placenta or colostrum in mother's milk).

Active Immunity

• Occurs when the body is exposed to antigens and produces its own antibodies and memory cells.
• Can be induced by immunisation (vaccines) or by natural infection.
• Provides long-term protection but requires time to develop.

Passive Immunity

• Occurs when ready-made antibodies are given directly (e.g. antitoxins, immune globulins) and gives immediate but short-term protection.
• Examples: maternal antibodies transferred via placenta and antibody-rich colostrum in breast milk (notably IgA in the gut of infants).

Vaccination and Immunisation

• Vaccines present antigenic components (attenuated, inactivated organisms or antigenic proteins) to stimulate antibody production and generate memory B and T cells for long-term protection.
• Passive immunisation: In emergencies where immediate protection is required (e.g. tetanus, snakebite), preformed antibodies or antitoxins are administered.
• Recombinant DNA technology: Enables production of antigenic polypeptides in bacteria or yeast for large-scale vaccine manufacture (example: hepatitis B vaccine produced in yeast).

Allergies

An allergy is an exaggerated immune response to normally harmless environmental antigens (allergens) such as pollen, dust mites or animal dander. Exposure stimulates production of IgE antibodies and sensitises mast cells and basophils.

Causes and Symptoms

• Causes: Immune overreaction to environmental particles (dust, pollen, pet dander).
• Symptoms: Sneezing, watery eyes, runny nose, wheezing and difficulty breathing.

Mechanism

• Exposure to an allergen leads to IgE production and sensitisation of mast cells.
• On re-exposure, mast cells release mediators such as histamine and serotonin causing allergic symptoms.
• Allergy testing exposes patients to small amounts of potential allergens and monitors reactions to identify causative agents.

Treatment

• Medicines include antihistamines, adrenaline (epinephrine for anaphylaxis) and steroids to control inflammation and symptoms rapidly.
• Environmental and lifestyle changes (reducing exposure to allergens) help reduce incidence; urban environmental changes have been linked to rising allergy and asthma rates in children.

Autoimmunity

Sometimes the immune system incorrectly recognises self components as foreign and attacks them, causing autoimmune diseases. Genetic and other factors contribute to loss of self-tolerance. An example is rheumatoid arthritis, where immune attack leads to chronic joint inflammation and damage.

Immune System in the Body

The immune system consists of organs, tissues, cells and molecules that recognise, respond to and remember foreign substances.

Lymphoid Organs

Primary lymphoid organs are sites of lymphocyte production and maturation; secondary lymphoid organs are sites where immune responses are initiated.

Diagrammatic representation of Lymph nodes

Primary lymphoid organs

• Bone marrow: Site of production of all blood cells including lymphocytes; B-cells mature in bone marrow.
• Thymus: Lobed organ above the heart where T-lymphocytes mature; large in infancy and involutes with age.

Secondary lymphoid organs

• Spleen: Filters blood, traps microorganisms and contains reserves of blood cells.
• Lymph nodes: Small structures along lymphatic vessels that trap antigens and activate lymphocytes.
• Tonsils: Located in the throat, they help trap pathogens entering via the mouth and nose.
• Peyer's patches: Lymphoid aggregates in the small intestine that monitor intestinal microbes.
• Appendix: Small pouch associated with the large intestine with putative immune functions.

Mucosa-Associated Lymphoid Tissue (MALT): Lymphoid tissue in the mucosal linings of major tracts (respiratory, digestive and urogenital) constitutes about half of the body's lymphoid tissue.

AIDS

AIDS stands for Acquired Immuno Deficiency Syndrome, indicating an immune deficiency acquired during life rather than congenital. It was first identified in 1981. Over the subsequent decades it has caused millions of deaths worldwide; the causative agent is the Human Immunodeficiency Virus (HIV), a retrovirus with an RNA genome enclosed in an envelope.

Replication of retrovirus

Transmission of HIV

• Sexual contact: Unprotected sexual intercourse with an infected person.
• Contaminated blood: Transfusion of infected blood or blood products.
• Shared needles: Use of contaminated needles among intravenous drug users.
• Mother to child: Vertical transmission across the placenta, during childbirth or through breast feeding.

Individuals at high risk: People with multiple sexual partners; intravenous drug users; those requiring frequent blood transfusions; children born to HIV-infected mothers.

HIV is not transmitted by casual contact; it is transmitted through certain body fluids. Stigmatisation of infected individuals is harmful; infected persons require medical care and social support.

HIV Replication and Immune System Impact

• HIV infects macrophages and helper T-lymphocytes (TH cells). Using its enzyme reverse transcriptase, the virus converts its RNA genome into DNA which integrates into host DNA.
• Infected cells produce new virus particles; persistent infection leads to progressive decline in helper T-cell numbers.
• Loss of TH cells impairs immune coordination, causing susceptibility to opportunistic infections (bacterial, viral, fungal and protozoan) and malignancies.

Diagnosis and Treatment

• Serological tests such as ELISA are commonly used for HIV screening and diagnosis.
• Antiretroviral therapy (ART): Combination antiretroviral drugs can suppress viral replication, prolong life and improve quality of life but do not eliminate the virus completely.

Prevention of AIDS

• Safe blood screening in blood banks.
• Use of disposable needles and syringes in healthcare settings.
• Promotion and free distribution of condoms.
• Control of intravenous drug abuse and needle-exchange programmes.
• Awareness of safe sexual practices and regular HIV testing for vulnerable populations.
• Organisations such as the National AIDS Control Organisation (NACO) and the World Health Organization (WHO) run prevention and education programmes.

Stigmatisation and Social Responsibility

• HIV/AIDS should not be hidden; concealment may increase spread.
• Infected individuals need compassion, medical care and social support, not ostracism.
• Addressing HIV/AIDS requires coordinated societal and medical efforts.

Cancer

• Cancer is the uncontrolled growth and proliferation of cells and is a leading cause of death worldwide.
• Regulation of cell growth and differentiation normally prevents uncontrolled proliferation; loss of these controls leads to malignancy.
• Contact inhibition is a property of normal cells to stop dividing on contact with neighbouring cells; cancer cells often lose this property.

Tumours

• Benign tumours: Localised and usually non-invasive.
• Malignant tumours: Invasive, can metastasise (spread) to distant sites and compete with normal tissues for nutrients.

Causes of Cancer

• Carcinogens: Agents that cause transformation of normal cells into cancerous ones.
• Physical agents: Ionising radiation (X-rays, gamma rays) and non-ionising radiation (ultraviolet light) can damage DNA.
• Chemical carcinogens: Substances in tobacco smoke are major causes of lung cancer.
• Biological agents: Oncogenic viruses carry viral oncogenes that may initiate cancer; activation of cellular proto-oncogenes (c-onc) can also lead to malignancy.

Cancer Detection and Diagnosis

• Early detection improves treatment success.
• Biopsy: Tissue sample examined histopathologically to confirm malignancy.
• Blood and bone marrow tests: Useful in haematological cancers such as leukemia.
• Imaging: Radiography, CT (computed tomography) and MRI (magnetic resonance imaging) help locate and stage tumours.
• Immunodiagnostics and molecular techniques: Antibodies to tumour antigens and molecular tests for susceptibility genes aid diagnosis and prevention strategies.

Treatment of Cancer

• Surgery: Removal of tumour and surrounding tissue where feasible.
• Radiation therapy: High-energy radiation to kill tumour cells while protecting normal tissue.
• Chemotherapy: Drugs to kill dividing cells; many have systemic side effects.
• Combination therapy: Most cancers are treated by combining surgery, radiation and chemotherapy for best outcomes.
• Immunotherapy: Boosting the immune response (e.g. interferons, checkpoint inhibitors) to target tumour cells.

Drugs and Alcohol Abuse

Drug and alcohol abuse is a growing public-health concern, particularly among the youth. Education, counselling and early intervention are crucial to prevent and treat substance misuse.

Commonly Abused Drugs

• Opioids, cannabinoids and coca alkaloids (cocaine) are commonly abused; many are plant-derived.

Opioids

• Opioids bind to specific opioid receptors in the central nervous system and gastrointestinal tract.
• Heroin (diacetylmorphine) is an opioid derived from morphine (from Papaver somniferum); commonly abused by snorting or injection.
• Opioids act as central depressants, slowing bodily functions and carrying risk of dependence and overdose.

Chemical Structure of Morphine

Cannabinoids

Chemical structure of Cannabinoid Molecule

• Cannabinoids act via cannabinoid receptors in the brain.
• Natural cannabinoids are obtained from Cannabis sativa; products include marijuana, hashish, charas and ganja.
• Consumption is usually by inhalation or oral ingestion; cardiovascular and cognitive effects may occur.

Leaves of Cannabis sativa

Coca Alkaloids (Cocaine)

• Derived from the coca plant Erythroxylum coca.
• Cocaine interferes with the transport and reuptake of the neurotransmitter dopamine, producing intense stimulation, euphoria and addictive behaviour.
• Common route of abuse is snorting; excessive use can lead to hallucinations and severe health consequences.

Flowering Branch of Datura

Hallucinogenic Plants and Prescription Drug Misuse

• Plants such as Atropa belladonna and Datura have hallucinogenic properties and have been used in traditional contexts; misuse carries serious risks.
• Prescription drugs (e.g. barbiturates, amphetamines, benzodiazepines, and sometimes morphine) may be misused, producing dependence and adverse effects.

Tobacco Use and Consequences

• Tobacco is used by smoking, chewing or sniffing and contains nicotine, which stimulates release of adrenaline and noradrenaline, raising blood pressure and heart rate.
• Smoking is linked to cancers (lung, urinary bladder, throat), bronchitis, emphysema, coronary heart disease and gastric ulcers.
• Tobacco chewing increases risk of oral cancers.
• Smoking raises blood carbon monoxide (CO), reducing oxygen carrying capacity and causing tissue hypoxia.
• Statutory warnings are present on packaging, yet use remains widespread among all age groups.

Conclusion

• Drug and alcohol abuse is a major concern; education and guidance are essential to help youth avoid harmful behaviours and adopt healthier lifestyles.
• Commonly abused substances include opioids, cannabinoids and coca alkaloids; each class has distinct pharmacological effects and health risks.
• Tobacco use causes serious long-term health problems including cancers and cardiovascular and respiratory diseases; prevention efforts must continue.

Adolescence and Drug/Alcohol Abuse

Adolescence is a developmental period (roughly ages 12-18) during which children mature emotionally, behaviourally and socially; it is a vulnerable time for initiation of substance use.

Key Characteristics of Adolescence

• Curiosity: Drives experimentation including with substances.
• Need for adventure: Risk-taking behaviours may increase susceptibility.
• Stress and pressure: Academic and social pressures may contribute to substance use as a coping mechanism.
• Social perception: Perceived 'coolness' of substance use influenced by peers and media.
• Family and peer influence: Unstable family environments and peer pressure are significant risk factors.

Initial experimentation can develop into reliance and addiction in some adolescents.

Addiction and Dependence

• Addiction: Psychological attachment to positive effects (euphoria, short-term relief) that compels repeated use despite harm.
• Tolerance: Repeated use reduces receptor sensitivity so higher doses are required to achieve the same effect, promoting escalation of use.
• Withdrawal: Stopping a regularly used substance can produce physical and psychological symptoms (anxiety, tremors, nausea, sweating) which may be alleviated by resuming use; severe withdrawal can be life-threatening and may need medical supervision.

Impact on Social Behaviour and Life

• Dependence can lead to neglect of social norms, financial difficulties and criminal behaviour to obtain substances.
• Family and social relationships often deteriorate; mental health and academic performance decline.

Immediate and Long-term Effects

• Immediate: Reckless behaviour, violence, overdose leading to coma or death (respiratory or cardiac failure).
• Long-term: Chronic damage to nervous system and liver (e.g. cirrhosis), higher risk of chronic infections (HIV, Hepatitis B) among injecting users, adverse effects on pregnancy and offspring.

Warning Signs Among Youth

• Decline in academic performance and unexplained absences.
• Neglect of personal hygiene, withdrawal and isolation.
• Depressive symptoms, fatigue, aggression and rebellious behaviour.
• Loss of interest in hobbies, changes in sleep and appetite, weight fluctuations.

Far-Reaching Implications

• Financial distress and possible involvement in theft to fund use.
• Impact on the mental and financial well-being of families and communities.
• Increased risk of blood-borne infections among intravenous drug users.

Misuse of Drugs in Sports

• Narcotic analgesics: Used to mask pain.
• Anabolic steroids: Used to increase muscle mass and strength.
• Diuretics: Used to reduce body weight quickly.
• Hormones: Used to enhance aggression or performance.

Side Effects of Anabolic Steroids

In females:

• Masculinisation, increased aggressiveness, mood swings and depression.
• Abnormal menstrual cycles, excessive hair growth, enlargement of the clitoris and voice deepening.

In males:

• Acne, increased aggressiveness, mood swings and depression.
• Testicular atrophy, reduced sperm production, risk of kidney and liver dysfunction, gynecomastia (breast enlargement), premature baldness and prostate enlargement.

In adolescents: Severe acne and premature closure of growth plates in long bones leading to stunted growth.

Prevention and Control

Prevention is preferable to cure. Substance misuse often begins in adolescence; early recognition and intervention reduce long-term harm. Parents, teachers and community play vital roles.

Parenting and Prevention

Positive parenting - combining nurturance with consistent discipline - is linked to lower risk of substance abuse.

• Avoiding peer pressure: Respect each child's personality and avoid pushing them beyond reasonable limits in studies, sports or activities.
• Education and counselling: Teach children coping strategies for stress, failure and disappointment; encourage engagement in positive activities (sports, music, reading, yoga).
• Seeking help: Encourage children to confide in parents or trusted peers; social support helps relieve anxiety and guilt.
• Identifying warning signs: Parents, teachers and friends should report and act on signs of substance use early to enable intervention.
• Professional help: Psychologists, psychiatrists and de-addiction centres provide assessment and rehabilitation services to those affected.