Revision: Human Health and Diseases Biology HSC Science (General) 12th Standard Board Exam Maharashtra State Board

It is to maintain a stable equilibrium of the body in accordance with the pressures and changes of the body environment.

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

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

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

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

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

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

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

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.

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.

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.

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.

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

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

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

Blood transfusion is the process of introducing blood from a healthy donor into the bloodstream of a patient, typically through a vein, often during surgery or after heavy blood loss.

Rhesus factor is a hereditary protein present in red blood cells. If present, the individual is Rh-positive; if absent, they are Rh-negative.

A Blood Recipient is a person who receives blood during a transfusion, requiring compatibility with the donor's blood group.

Antigens are specific proteins present on the surface of red blood cells that determine an individual’s blood group (e.g., Antigen A or Antigen B).

Antibodies are proteins present in blood plasma that react against specific antigens not found on the individual's own red blood cells, playing a key role in blood group compatibility.

A person with blood group AB is called a universal recipient because they can receive blood from all major blood groups (A, B, AB, and O) without risk of incompatibility.

Disease:
The disease can be defined as an impairment or malfunctioning of the normal state of the living organism that disturbs or modifies the performance of vital functions of the body.

A pathogen is a biological agent that causes disease to its host. e.g. bacteria, virus, etc.

Any deviation from normal state of health is called disease.

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.

Adolescence is the period between the beginning of sexual maturation and entry into adult life.

Addiction is a condition of physical and psychological dependence on a substance or habit, leading to compulsive use despite harmful effects.

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

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

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

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.

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

• 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.

• 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).

• Two Main Cell Types: Lymphocytes and Antigen Presenting Cells (APCs), both originating from hematopoietic stem cells.
• Lymphocytes: B-lymphocytes (differentiate in bursal lymphoid tissues) handle humoral immunity; T-lymphocytes (differentiate in the thymus) handle cell-mediated immunity.
• T-lymphocyte Clones: On antigen contact, T-cells form — Helper, Killer/Cytotoxic, Suppressor, and Memory T-cells.
• B-lymphocytes & Plasma Cells: Activated B-cells produce plasma cells (secrete antibodies) and memory B-cells.
• Antibody Functions: Agglutination, opsonisation, and neutralisation.
• APCs: Dendritic cells, macrophages, and B-cells engulf pathogens, process antigens, and present them on their surface to activate Helper T-cells.

• 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.

• Nature: Y-shaped glycoproteins called Immunoglobulins (Igs), produced by plasma cells at ~2000 molecules per second.
• Structure: Made of 4 polypeptide chains — 2 Heavy (H) and 2 Light (L) chains, held by disulphide bonds.
• Regions: Each chain has a Variable region (antigen-binding site) and a Constant region. The junction between arms and stem is the hinge.
• Antigen Binding: Variable region (paratope) binds to a specific antigen, forming an antigen-antibody complex. Most antibodies have two binding sites — called bivalent.
• Types: Five immunoglobulins — IgG, IgM, IgA, IgE, and IgD.

• Serology: The study of antigen-antibody interactions is called serology.
• Key Terms: Combining sites on antigen = Epitopes; binding sites on antibody = Paratopes (on variable region).
• Lock & Key Mechanism: Epitopes bind paratopes in a lock and key manner to form the antigen-antibody complex. Small variations in the variable region make each antibody highly specific.
• Antigen on Blood Cells: RBCs carry several antigens giving rise to different blood groups — ABO, Rh, Duffy, Kidd, MNS, Bombay, etc. (genetically determined).
• Specificity: Each antibody binds only to its specific antigen, imparting individuality to all humans.

• ABO System: Introduced by Karl Landsteiner (1900). Based on the presence/absence of antigen A and B on RBCs, four groups: A, B, AB, O.
• Universal Donor & Acceptor: AB = universal acceptor (both antigens, no antibodies); O = universal donor (no antigens, both antibodies).
• Rh Factor: Discovered by Landsteiner & Wiener (1940). 80–85% people are Rh⁺; the rest are Rh⁻.
• HDN (Erythroblastosis Foetalis): When a Rh⁻ mother carries a Rh⁺ foetus, she produces anti-Rh antibodies (after the first delivery), which attack subsequent Rh⁺ foetuses.
• Prevention: Rh⁻ mother is injected with anti-D antibodies during all pregnancies with Rh⁺ foetus to prevent HDN.

• 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.

• 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.

• Adolescence is the stage between childhood and adulthood (ages 10–19), marked by fast physical and emotional changes.
• It has three stages: Early (10–14), Middle (15–17), and Late (18–19), each with different body and thinking developments.
• Puberty brings sexual and physical changes due to hormones—testosterone in boys and oestrogen in girls.
• Physical changes include growth in height, changes in body shape, changes in voice, and increased sweat/oil production.
• Emotional and social changes include mood swings, seeking independence, peer pressure, and identity formation.

• Meaning: Physical, mental, and physiological dependence on habits (gambling) or substances (nicotine, alcohol, drugs) despite harmful consequences.
• Brain Mechanism: Involves the brain's reward & reinforcement pathways using the neurotransmitter dopamine, affecting motivation.
• Reversibility: Neurological changes are reversible once substance use or behaviour is stopped.
• Effects: Impairs physical, physiological, and psychological functions of the body.
• Causes in Adolescents: Insufficient parental supervision, lack of communication, family conflicts, risk-taking behaviour, and favourable parental attitudes towards drugs/alcohol.

• 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.

• 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.