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 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 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.

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.

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.

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

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

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

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.

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.

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

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.

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.

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.

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

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

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.

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

The process of introducing weakened or inactivated pathogens or their antigenic components into the body to induce immunity is called as vaccination.

The process by which an individual acquires protection against a specific disease through vaccination or antibody administration is called as immunisation.

The process of providing immediate protection by injecting preformed antibodies into the body is called as passive immunisation.

The exaggerated or hypersensitive immune response of the body to certain harmless environmental substances is called as allergy.

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

The condition in which the immune system fails to distinguish self from non-self and attacks the body’s own cells is called as autoimmunity.

A state of complete physical, mental and social well-being and not merely the absence of disease or infirmity is called health.

Adverse functioning of one or more organs or systems of the body, characterised by specific signs and symptoms, is called disease.

Diseases that are easily transmitted from one person to another are called infectious diseases.

Diseases that do not spread from one person to another and arise due to genetic factors, lifestyle or physiological disorders are called non-infectious diseases.

Organisms such as bacteria, viruses, fungi, protozoans and helminths that cause diseases in humans are called pathogens.

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.

• WHO Health = Complete physical, mental and social well-being; not merely absence of disease.
• Immunity = Ability of the host to fight disease via the immune system; distinguishes self from non-self.
• Antigen = foreign substance stimulating an immune response; Antibody = protective chemical produced against antigens.
• Concept started by Edward Jenner — developed cowpox vaccine against smallpox. Study of the immune system = Immunology.
• Memory Cells — Formed after infection; live for years; on second invasion → rapidly multiply → faster, stronger response → explains why childhood diseases are not contracted twice.

• Meaning: Non-specific, hereditary defence present from birth; not affected by prior infection or vaccination.
• Physical Barriers: Skin, mucus lining, nasal hair, cough reflex, and flushing action of urine/tears block microbial entry.
• Physiological Barriers: Stomach acid, saliva, and tears (containing Lysozyme) prevent microbial growth.
• Cellular Barriers: Neutrophils, monocytes, and macrophages destroy microbes via phagocytosis; NK cells fight viruses and tumours.
• Cytokine Barriers: Infected cells release interferons to protect neighbouring cells from viral infection.
• Blood Proteins: The complement system (30+ proteins) eliminates pathogens; Acute Phase Proteins (CRP, etc.) surge during infection to aid repair and resistance.

• Meaning: Immunity developed during lifetime; also called Adaptive/Specific immunity. Works by producing antibodies against specific antigens.
• Key Features: Specificity, Diversity, Self vs Non-self discrimination, and Memory (faster response on second exposure to the same pathogen).
• Active Immunity: The body produces its own antibodies. Natural — after infection (e.g., measles, lifelong). Artificial — via vaccines (e.g., Polio, BCG).
• Passive Immunity: Ready-made antibodies received externally. Natural — from mother via placenta/colostrum. Artificial — injected serum from immunised animals (e.g., anti-rabies from horses).
• Key Difference: Active immunity is long-lasting (memory cells formed); Passive immunity is short-lived (no memory cells).

• 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.

• Principle: Works on the immune system's memory. A vaccine (weakened/inactivated pathogen or its proteins) stimulates antibody production and generates memory B and T-cells.
• On Re-exposure: Memory cells quickly recognise the pathogen and produce massive antibodies to neutralise it.
• Passive Immunisation: Preformed antibodies/antitoxins are directly injected when quick response is needed (e.g., tetanus, snakebite).
• Types of Vaccines: Protein/sugar from pathogen, dead/inactivated pathogen, toxoid, or attenuated (weakened) pathogen.
• Recombinant DNA Vaccines: Antigenic polypeptides produced in bacteria/yeast for large-scale production (e.g., Hepatitis B vaccine from 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.

• Chemicals: Nicotine, caffeine, polycyclic hydrocarbons, coal/oil combustion products, and excess sex hormones are carcinogenic (e.g., breast cancer linked to hormones).
• Radiation: X-rays, gamma rays, UV rays, and cosmic rays cause cancer. High UV exposure increases the risk of skin cancer.
• Viruses: Oncogenic viruses carry v-onc genes (e.g., EBV, HPV).
• Oncogenes: Normal cells contain proto-oncogenes (c-onc genes), which, when activated, transform cells into cancerous ones.
• Addiction: Tobacco → mouth, lips, lung cancer; Alcohol → oesophagus, liver cancer; Drugs (marijuana, steroids) → also cause cancer.

• 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.

• Dependence: Repeated use of drugs/alcohol creates a psychological attachment. Stopping suddenly causes withdrawal syndrome.
• Immediate Effects: Reckless behaviour, violence, heart failure, cerebral haemorrhage — may lead to coma and death.
• Long-term Effects: Mental and financial distress to the addict and family. Chronic use causes nervous system damage and liver cirrhosis. Alcohol use in adolescence may lead to heavy drinking in adulthood.
• Prevention Measures: Avoid undue peer pressure, seek education and counselling, maintain open communication with parents, and look out for danger signs early.
• Medical Help: Professional and medical help should be sought immediately upon identifying signs of drug/alcohol abuse — early intervention improves recovery.

• The immune system consists of lymphoid organs, tissues, cells and soluble molecules like antibodies that protect the body against foreign antigens.
• It has the unique ability to recognise antigens, respond to them and retain memory for faster and stronger responses on repeated exposure.
• Primary lymphoid organs (bone marrow and thymus) are responsible for the origin, development and maturation of lymphocytes.
• Secondary lymphoid organs such as spleen, lymph nodes, tonsils, Peyer’s patches and appendix are sites where lymphocytes interact with antigens and initiate immune responses.
• Mucosa-associated lymphoid tissue (MALT), present in respiratory, digestive and urogenital tracts, forms nearly 50% of the body’s lymphoid tissue and provides defence at body surfaces.