Revision: Class 12 >> Human Health and Diseases NEET (UG) Human Health and Diseases

Health is defined as the state of complete physical, mental, and social well-being and not merely the absence of disease or infirmity.

The overall ability of the host to fight the disease-causing organisms conferred by the immune system is called immunity.

The study of the immune system and immune responses is called immunology.

Innate immunity is the inborn, non-specific defence that protects the body from pathogens from birth.

The immunity developed when the body produces its own antibodies in response to exposure to antigens through infection or vaccination is called as active immunity.

The immunity obtained by the direct transfer of ready-made antibodies from another individual is called as passive immunity.

Acquired immunity is the specific defence developed after exposure to a pathogen, characterised by memory and a stronger response on re-exposure.

The immunity obtained by the direct transfer of ready-made antibodies from another individual is called as passive immunity.

Acquired immunity is the specific defence developed after exposure to a pathogen, characterised by memory and a stronger response on re-exposure.

The immunity developed when the body produces its own antibodies in response to exposure to antigens through infection or vaccination is called as active immunity.

Infection is the entry, development, or multiplication of an infectious agent in the human body or animals.

A preparation containing specific antigens that is administered to induce temporary or permanent immunity against a particular disease is called a vaccine.

The process of administering a vaccine to stimulate the immune system and provide protection against infectious diseases is called vaccination.

Preparation of antigenic proteins of pathogens (weakened or killed) which on inoculation into a healthy person provides temporary/permanent immunity against a particular disease.

Antibiotics are metabolic products of microorganisms whose very low concentrations are inhibitory or detrimental to other microbes.

The substance that triggers an allergic immune response in a sensitive individual is called an allergen.

The exaggerated response of the immune system to certain antigens present in the environment is called an allergy.

Allergies, also known as allergic diseases, are a number of conditions caused by hypersensitivity of the immune system to something in the environment that usually causes no adverse effects to most people. These diseases include hay fever, dermatitis, asthma, food allergies, etc.

Autoimmunity is the condition in which the immune system fails to recognise self and reacts against the body’s own cells and tissues.

Autoimmune response is an immune reaction in which antibodies or immune cells are produced against the body’s own antigens.

Autoimmune disease is a pathological condition caused due to autoimmunity, where self-tissues are damaged or destroyed by the immune system.

The defence mechanism involving lymphocytes and macrophages without antibody production is called cell-mediated (cellular) immune response.

The system of defence mechanisms that protects the body against harmful agents is called immune system.

The antibody-mediated defence mechanism is called humoral immune response.

The immunity developed during an individual’s lifetime after exposure to antigens is called acquired (specific) immunity.

The hereditary, non-specific protection present from birth is called innate (natural) immunity.

Malignant tumour is a cancerous tumour that grows rapidly, invades surrounding tissues and spreads to distant organs.

Benign tumour is a non-cancerous tumour that remains confined to its original site and does not spread to other parts of the body.

Cancer is a disease characterised by uncontrolled and abnormal division of body cells due to loss of normal growth regulation.

Metastasis is the process by which cancer cells spread from the primary site to distant organs through blood or lymph.

Tumour is a mass of abnormally proliferating cells formed due to uncontrolled cell division.

Agents that cause cancer by disturbing the normal genetic and regulatory processes of cells are called carcinogens.

A cancer-causing gene that induces transformation of normal cells into cancerous cells is called an oncogene.

A normal cellular gene involved in growth and development, which can become an oncogene after mutation or activation, is called a proto-oncogene.

Drug abuse is the improper or excessive use of drugs that leads to harmful effects on physical, mental and social health.

• Health is a state of complete physical, mental, and social well-being — not just the absence of disease.
• Health is affected by genetic disorders, infections from microbes, and lifestyle (food, water, exercise, rest).
• Good health is maintained by a balanced diet, personal hygiene, regular exercise, immunisation, and vector control.
• Diseases are of two types: infectious (transmitted person to person) and non-infectious (cannot be transmitted).
• Disease-causing organisms are called pathogens - they include bacteria, viruses, fungi, protozoans, and helminths.
• Pathogens enter the body, multiply, and disrupt vital functions; they adapt to the host environment (e.g., survive low pH in the gut).

• Typhoid is caused by Salmonella typhi and spreads through contaminated food and water.
• Typhoid symptoms include high fever, weakness, stomach pain, and loss of appetite; confirmed by the Widal test.
• Pneumonia is caused by Streptococcus pneumoniae and Haemophilus influenzae and spreads through air droplets.
• Pneumonia affects the lungs, causing fluid-filled alveoli, cough, fever, and breathing difficulty.
• Other bacterial diseases include dysentery, cholera, tuberculosis, tetanus, and plague.
• These diseases spread through various modes like contaminated food/water, air droplets, direct contact, or insect vectors.
• Severe infections can lead to serious complications or death if untreated.

• Common cold is caused by Rhinovirus, spreads via droplets from cough/sneezes and contaminated objects, with symptoms like nasal congestion, sore throat, and headache, lasting 3-7 days.
• Dengue and Chikungunya are both spread by the Aedes mosquito; Dengue is caused by the Dengue virus and Chikungunya by the CHIK virus.
• Influenza spreads via coughing/sneezing, Measles spreads via droplets, while Mumps and Chickenpox spread through airborne droplets.
• German measles spreads via close contact, Smallpox via direct contact, and Rabies is transmitted through the bite of a rabid dog.
• Polio is caused by the polio virus and spreads via faeces and air, seriously affecting the nervous system.
• Avian flu is caused by the H5N1 virus and spreads through contact with infected poultry as well as through airborne spread.
• Chickenpox is caused by Varicella zoster and spreads via airborne droplets, while Smallpox, caused by Variola virus, spreads via direct contact and is now globally eradicated.

• Ascariasis is caused by Ascaris and spreads through faeces-contaminated soil, water, vegetables, and fruits.
• Symptoms of Ascariasis - internal bleeding, muscular pain, fever, anaemia, and intestinal blockage.
• Filariasis is caused by Wuchereria bancrofti and W. malayi, transmitted by female Culex mosquito bite.
• Filarial worms live in the lymphatic vessels of the lower limbs, causing chronic inflammation for many years.
• Filariasis leads to deformity of limbs and genital organs due to long-term swelling.

• Ringworm is caused by fungi Microsporum, Trichophyton, and Epidermophyton.
• It spreads from soil or by sharing an infected person's towels, clothes, and comb; heat and moisture help fungi grow.
• Symptoms include dry, scaly lesions on the skin, nails, and scalp with intense itching.
• Ringworm commonly appears in the groin area and between the toes.

1. Hygiene: Maintaining personal hygiene (clean food/water) and public sanitation (waste disposal) prevents waterborne diseases such as typhoid and amoebiasis.
2. Isolation: Avoiding close contact with infected individuals and their belongings helps prevent airborne diseases such as pneumonia and the common cold.
3. Vector Control: Eliminating stagnant water, using mosquito nets, and introducing Gambusia fish controls insect-borne diseases like malaria and dengue.
4. Vaccination: Immunisation programs successfully eradicate (e.g., smallpox) or control (e.g., polio, tetanus) deadly infectious diseases.
5. Medical Advances: The use of antibiotics and the development of newer vaccines through biotechnology enable effective disease treatment and prevention.

• Immunology studies the immune system, while immunity is the host's ability to fight disease-causing organisms.
• Body defence works at two levels: external local barriers that prevent entry, and the internal immune system that fights invading germs.
• The immune system can accurately distinguish between the body's own cells (self) and foreign invaders (non-self).
• Foreign substances that trigger an immune response are antigens, and the protective chemicals produced against them are antibodies.
• Stimulated lymphocytes divide into active effector cells (to fight the immediate infection) and dormant memory cells.
• Memory cells stay in the lymph nodes to mount a much faster and stronger immune response upon subsequent encounters with the same antigen.

• Innate immunity is a non-specific, natural defence present at birth that prevents the entry of and destroys foreign agents.
• Physical barriers, such as the skin and mucous membranes, physically block and trap invading microorganisms.
• Physiological barriers utilise bodily secretions - like stomach acid, saliva, and lysozyme in tears - to inhibit or destroy microbial growth.
• Cellular barriers rely on phagocytic cells (neutrophils, macrophages) and Natural Killer cells to actively ingest and destroy pathogens.
• Cytokine barriers consist of interferons, which are secreted by virus-infected cells to protect surrounding healthy cells from further viral infection.
• Additional systemic defences include fever, the complement protein system, and acute-phase proteins that enhance host resistance and eliminate pathogens.

• Acquired immunity is a pathogen-specific defence system developed over a lifetime that remembers infections and forms the basis of vaccination.
• Its main features include specificity against distinct pathogens, diversity in recognising various antigens, self/non-self recognition, and immunological memory.
• Initial pathogen exposure causes a low-intensity primary response, while later exposures trigger a much faster and stronger secondary response due to memory cells.
• B-lymphocytes produce protective proteins called antibodies (structured as H₂L₂), and T-lymphocytes help B-cells while mediating cellular responses.
• The immune response is classified as either humoral (antibody-mediated in the blood) or cell-mediated (T-cell mediated, responsible for graft rejection).
• Immunity can be active (the body produces its own antibodies, providing long-term protection) or passive (the body receives ready-made antibodies for immediate, short-term protection).

• Acquired immunity is a pathogen-specific defence system developed over a lifetime that remembers infections and forms the basis of vaccination.
• Its main features include specificity against distinct pathogens, diversity in recognising various antigens, self/non-self recognition, and immunological memory.
• Initial pathogen exposure causes a low-intensity primary response, while later exposures trigger a much faster and stronger secondary response due to memory cells.
• B-lymphocytes produce protective proteins called antibodies (structured as H₂L₂), and T-lymphocytes help B-cells while mediating cellular responses.
• The immune response is classified as either humoral (antibody-mediated in the blood) or cell-mediated (T-cell mediated, responsible for graft rejection).
• Immunity can be active (the body produces its own antibodies, providing long-term protection) or passive (the body receives ready-made antibodies for immediate, short-term protection).

• Vaccination and immunisation work on the immune system's memory.
• A vaccine may contain a weakened pathogen, an inactivated pathogen, or antigenic proteins.
• The body produces antibodies against these antigens.
• Memory B-cells and T-cells enable a faster response during later exposure.
• Passive immunisation involves direct injection of preformed antibodies or antitoxins.
• Examples of passive immunisation include tetanus and snakebite treatment.
• Vaccines may be made from protein or sugar from a pathogen, a dead or inactivated pathogen, a toxoid, or a weakened pathogen.
• Antigenic polypeptides can also be produced using recombinant DNA technology in bacteria or yeast.

• An allergy is an exaggerated immune response to environmental antigens.
• IgE is the antibody involved in allergic reactions.
• Histamine and serotonin released from mast cells are responsible for allergic symptoms.
• H1 receptors are related to allergic manifestations, whereas H2 receptors are related to gastric acid secretion.
• Severe systemic allergy is called anaphylactic shock.
• Diagnosis is done by testing with small doses of allergens.
• Antihistamines, adrenaline, steroids, and sodium cromoglycate are used in treatment.

• Autoimmunity is a condition where the immune system loses its ability to distinguish between "self" and "non-self" cells, mistakenly targeting the body's own tissues.
• An autoimmune response is a specific abnormal reaction in which the body actively produces antibodies or immune cells directed against its own self-antigens.
• Autoimmune disease is the resulting pathological condition where this misdirected immune response causes actual physical damage and destruction to self-tissues.
• Common examples include Rheumatoid arthritis, Hashimoto’s disease (targeting the thyroid), myasthenia gravis (targeting muscles), Addison’s disease, and chronic anaemia (targeting red blood cells).

• The immune system defends the body against infectious agents and consists of lymphoid organs, tissues, cells, and soluble molecules like antibodies.
• Primary lymphoid organs (bone marrow and thymus) are the sites where immature lymphocytes originate, develop, and differentiate into antigen-sensitive cells.
• Secondary lymphoid organs (spleen, lymph nodes, tonsils, and MALT) provide the specific sites where mature lymphocytes interact with antigens and proliferate.
• The spleen acts as a blood filter, trapping blood-borne microorganisms, while lymph nodes trap antigens in the lymphatic fluid, triggering localised immune responses.
• The humoral immune response is driven by specific lymphocytes that produce circulating antibodies to bind, neutralise, and eliminate foreign antigens.
• The cellular immune response does not involve circulating antibodies, but instead relies on the direct cooperation of lymphocytes and macrophages to destroy pathogenic organisms.

• AIDS is a fatal, non-congenital condition caused by HIV, leading to severe immune system deficiency.
• HIV is a spherical retrovirus featuring two single-stranded RNA molecules, the enzyme reverse transcriptase, and a lipid envelope with specific glycoproteins.
• The virus targets and destroys CD4 (T4) helper T-cells and uses macrophages as replication factories, progressively weakening the host's immune response.
• Transmission occurs through contact with infected body fluids, specifically via sexual intercourse, contaminated blood transfusions, shared needles, or from mother to child.
• Individuals at high risk include those with multiple sexual partners, intravenous drug users, recipients of repeated blood transfusions, and children born to infected mothers.
• Diagnosis involves a primary screening test called ELISA, followed by a highly specific confirmatory test known as Western Blot.
• While there is no cure, antiretroviral drugs like AZT can partially reduce viral load and extend patients' lifespans.
• Prevention - including education, safe sexual practices, blood screening, and the use of disposable needles - is critical, supported by social sympathy for those living with HIV.

• Carcinogens disrupt normal cellular genetics, potentially transforming growth-regulating proto-oncogenes into cancer-causing oncogenes.
• Chemical factors such as nicotine, polycyclic aromatic hydrocarbons, and imbalanced sex hormones are known to induce various cancers.
• Radiation acts as a physical carcinogen, with ionising (e.g., X-rays) and non-ionising (e.g., UV rays) radiation damaging DNA and increasing cancer risk.
• Biological factors such as oncogenic viruses (e.g., HPV and EBV) carry viral oncogenes that can transform normal cells into cancerous ones.
• Lifestyle habits, particularly smoking, tobacco chewing, and alcohol abuse, significantly heighten the risk for multiple types of cancer.

• Cancer is detected through biopsy (tissue sample stained and examined under a microscope), histopathological studies, and blood/bone marrow tests (for leukaemia).
• CT scan uses X-rays to produce 3D images of internal organs; MRI uses strong magnetic fields and non-ionising radiation to detect tissue changes.
• Antibodies against cancer-specific antigens are also used for detecting certain cancers.
• Molecular biology techniques identify genes associated with inherited cancer susceptibility, helping in early prevention.
• Individuals with inherited cancer susceptibility are advised to avoid specific carcinogens, e.g., tobacco smoke in case of lung cancer.

• Opioids: Source - Papaver somniferum (poppy). Effect - depressant, pain killer. Example - Heroin (diacetyl morphine).
• Cannabinoids: Source - Cannabis sativa (hemp). Effect - daydreaming affects the cardiovascular system. Examples - Marijuana, hashish, charas, ganja.
• Cocaine: Source - Erythroxylum coca. Effect - stimulates the CNS, causes euphoria, irritability, paranoia. Example - Cocaine.
• Hallucinogens: Source - Atropa belladonna, Datura. Effect - unreal perceptions of unreal objects. Examples - LSD, cannabis.
• General Effect: All abused drugs cause addiction, dependence, and impair physical, physiological, and psychological functions.

• Adolescence (12-18 years) bridges childhood and adulthood; marked by biological and behavioural changes, making it a vulnerable phase for mental development.
• Curiosity, excitement, and a need for adventure are the main reasons youngsters are drawn towards drugs and alcohol.
• Drug/alcohol use starts with curiosity but later becomes a means to escape stress and academic pressure.
• Perception of drugs/alcohol being 'cool' and media promotion are major causes for youth starting these habits.
• Unsupportive family structures and peer pressure are major contributing factors to drug/alcohol abuse in adolescents.

• Addiction is a psychological attachment to drug-induced effects like euphoria and well-being, driving users to continue despite harmful consequences.
• Repeated exposure increases the tolerance of body receptors, necessitating higher doses to achieve the same effect.
• Even a single use of these substances can act as a forerunner to a persistent cycle of abuse.
• Dependence occurs when the body manifests an unpleasant withdrawal syndrome - including anxiety, nausea, shakiness, and sweating - upon the abrupt discontinuation of regular use.
• Severe dependence may cause individuals to disregard social norms to secure funds for their needs, leading to significant social and adjustment problems.

• Immediate adverse effects include reckless behaviour, violence, and life-threatening conditions such as respiratory failure, heart failure, or cerebral haemorrhage due to overdose.
• Long-term use leads to chronic damage to the liver (cirrhosis) and nervous system, affects fetal development, and can cause pancreatitis or loss of balance in adolescents.
• Intravenous drug abuse involving shared needles carries a high risk of transmitting serious infections, specifically AIDS and Hepatitis B.
• Behavioural and social consequences include academic decline, isolation, aggression, and potential criminal behaviour like stealing to fund the addiction, causing distress to family and friends.

• The principle of "prevention is better than cure" is vital because substance use often begins during adolescence, necessitating early identification of risky situations by parents and teachers.
• Nurturing parenting that incorporates consistent discipline is associated with a lowered risk of tobacco, alcohol, and drug abuse.
• Prevention efforts include avoiding undue peer pressure, respecting individual personality, providing counselling to manage stress and failure, and encouraging healthy extracurricular activities.
• If danger signs are identified, seeking guidance from trusted friends, parents, or professionals - such as psychologists, psychiatrists, and rehabilitation programs - is essential for successful recovery and a return to a healthy life.