Human Health and Disease

The One Thing

Human health depends on physical, mental, and social well-being, while disease results from harmful changes that disturb normal body functions. Prevention, immune protection, early detection, appropriate treatment, and social support are central to controlling infectious and non-infectious diseases.

Reactions, Processes and Experiments

Key Terms

• Health: A state of physical, mental, and social well-being, not merely the absence of disease.
• Disease: A condition that disturbs the normal structure or functioning of the body.
• Infectious disease: A disease caused by disease-producing organisms and capable of spreading from one person or source to another.
• Pathogen: An organism or infectious agent that causes disease, such as a bacterium, virus, protozoan, or worm.
• Common cold: A viral infection of the upper respiratory tract, commonly caused by rhinoviruses; it spreads through droplets and contaminated objects.
• Pneumonia: An infection of the lungs in which alveoli may fill with fluid, commonly caused by bacteria such as Streptococcus pneumoniae or viruses.
• Malaria: A disease caused by Plasmodium parasites and transmitted through the bite of an infected female Anopheles mosquito.
• Plasmodium: The protozoan parasite responsible for malaria; its asexual multiplication in red blood cells causes periodic fever and chills.
• Typhoid: A bacterial disease caused by Salmonella typhi, usually transmitted through contaminated food and water.
• Ascariasis: A worm infection caused by Ascaris lumbricoides, commonly acquired by consuming food or water contaminated with eggs.
• Amoebiasis: An intestinal infection caused by Entamoeba histolytica, often spread through contaminated food and water.
• Immunity: The ability of the body to resist or control infection and disease.
• Innate immunity: The non-specific, inborn defense system present from birth.
• Physical barriers: First-line defenses such as skin, mucus, and ciliated epithelium that prevent pathogen entry.
• Physiological barriers: Chemical defenses such as acidic conditions in the stomach, lysozyme in tears and saliva, and body temperature.
• Cellular barriers: Defense provided by cells such as neutrophils, monocytes, macrophages, and natural killer cells.
• Cytokine barriers: Defense molecules, especially interferons, released by virus-infected cells to protect nearby cells.
• Acquired immunity: Specific immunity that develops during a person's lifetime and has memory of previously encountered antigens.
• Antigen: A foreign substance that triggers a specific immune response.
• Antibody: A specific immunoglobulin protein produced by B lymphocytes or plasma cells in response to an antigen.
• B lymphocytes: Immune cells that differentiate into plasma cells and produce antibodies.
• T lymphocytes: Immune cells involved in cell-mediated immunity, including activation of other immune cells and destruction of infected cells.
• Primary immune response: The slower and usually weaker response produced when an antigen enters the body for the first time.
• Secondary immune response: A faster and stronger response caused by memory cells when the same antigen enters the body again.
• Vaccination: The introduction of a harmless form or component of a pathogen to stimulate protective immune memory.
• Active immunity: Immunity produced by the person's own immune system after infection or vaccination.
• Passive immunity: Immunity obtained by receiving ready-made antibodies, such as maternal antibodies through colostrum or injected antiserum.
• Allergy: An exaggerated immune response to normally harmless substances called allergens.
• Autoimmunity: A condition in which the immune system attacks the body's own cells or tissues.
• AIDS: Acquired Immunodeficiency Syndrome, a condition in which HIV progressively weakens the immune system.
• HIV: Human Immunodeficiency Virus, a retrovirus that infects helper T lymphocytes and reduces immune defense.
• Reverse transcriptase: An enzyme in retroviruses that forms DNA using viral RNA as a template.
• Cancer: A group of diseases involving uncontrolled cell division, abnormal growth, and possible invasion of nearby or distant tissues.
• Oncogene: A gene that can promote cancerous growth when activated or altered.
• Tumour: An abnormal mass of cells formed by uncontrolled cell division; it may be benign or malignant.
• Benign tumour: A localized tumour that generally does not invade surrounding tissues or spread to distant organs.
• Malignant tumour: A cancerous tumour that invades tissues and may spread through blood or lymph.
• Metastasis: The spread of cancer cells from the original site to other parts of the body.
• Carcinogen: A cancer-causing agent, such as certain chemicals, tobacco smoke, radiation, or some viruses.
• Drug abuse: The harmful or non-medical use of drugs that can cause dependence, health damage, and social problems.
• Addiction: A strong physical or psychological dependence on a substance, often accompanied by loss of control over its use.
• Withdrawal symptoms: Unpleasant physical or psychological effects that occur when a dependent person stops taking a drug.
• Opioids: Drugs derived from or related to opium that affect the nervous system and may cause dependence; examples include heroin and morphine.
• Cannabinoids: Compounds obtained from Cannabis that affect brain function and may impair coordination, memory, and judgment.
• Cocaine: A stimulant obtained from the coca plant that produces short-term excitement but can cause dependence and serious cardiovascular effects.

Easily Confused

• Health and absence of disease: Health includes physical, mental, and social well-being; it is not merely the absence of disease.
• Infectious and non-infectious disease: Infectious diseases are caused by pathogens and can spread; non-infectious diseases result from factors such as genetics, lifestyle, environmental conditions, or uncontrolled cell growth.
• Innate and acquired immunity: Innate immunity is non-specific, immediate, and present from birth; acquired immunity is antigen-specific and develops memory.
• Active and passive immunity: Active immunity is produced by the person's own immune system after infection or vaccination; passive immunity results from receiving ready-made antibodies.
• Primary and secondary immune responses: The primary response is slower and weaker after first exposure; the secondary response is faster and stronger because of memory cells.
• Antigen and antibody: An antigen triggers an immune response; an antibody is the specific immunoglobulin produced against it.
• Benign and malignant tumours: Benign tumours are generally localized; malignant tumours invade tissues and may spread.
• HIV and AIDS: HIV is the virus; AIDS is the condition resulting from progressive weakening of the immune system by HIV.
• Radiotherapy and chemotherapy: Radiotherapy uses directed high-energy radiation; chemotherapy uses anti-cancer drugs.
• Drug abuse and dependence: Drug abuse is harmful or non-medical use; dependence is the physical or psychological reliance that may produce withdrawal symptoms.
• Antibiotics and viral infection: Antibiotics are suitable for certain bacterial infections but are ineffective against viral infections such as the common cold.
• Disease transmission and casual contact: HIV transmission occurs through identifiable routes such as sexual contact, infected blood, contaminated needles, or mother-to-child transmission, not through handshakes, hugging, sharing food, or mosquito bites.

What Gets Asked

• Define health and disease, and distinguish infectious from non-infectious disease. Marks are lost by treating health as merely the absence of disease or by omitting the role of pathogens in infectious disease.
• Describe named diseases such as the common cold, pneumonia, malaria, typhoid, ascariasis, and amoebiasis, including their causative organisms and routes of transmission. For malaria, the specific Anopheles–Plasmodium transmission cycle and haemozoin-associated fever are important.
• Explain the four components of innate immunity and compare innate immunity with acquired immunity. A common error is to describe innate immunity as antigen-specific or to omit cytokine barriers and interferons.
• Explain primary and secondary immune responses, vaccination, active immunity, passive immunity, and the role of colostrum and IgA. Marks are lost by confusing immunity produced by the person's own immune system with immunity obtained from ready-made antibodies.
• Describe HIV transmission, infection of helper T cells, diagnosis by tests such as ELISA, and methods of control. HIV should not be stated to spread through casual contact or mosquito bites; antiretroviral therapy suppresses viral multiplication but is not a complete cure.
• Explain cancer development, benign and malignant tumours, metastasis, risk factors, diagnosis, and treatment. Distinctions between radiotherapy and chemotherapy, and between localized and invasive tumours, must be stated accurately.
• Discuss drug abuse, addiction, withdrawal symptoms, risk factors among adolescents, effects on body systems and social life, and prevention or rehabilitation. Dependence should be treated as a medical and psychological health concern rather than a moral failure.