Human Health and Diseases

The One Thing

Human health depends on physical, mental, and social well-being and is protected through personal habits, immune defenses, medical care, sanitation, and public-health measures. Disease may result from pathogens, genetic or cellular abnormalities, environmental conditions, or unhealthy habits, so prevention and timely treatment are central.

Reactions, Processes and Experiments

Key Terms

• Health: A state of complete physical, mental, and social well-being, not merely the absence of disease.
• Disease: An abnormal condition that interferes with the normal structure or functioning of the body.
• Pathogen: A disease-causing organism or infectious agent, such as a bacterium, virus, protozoan, fungus, helminth, or abnormal cell.
• Communicable disease: A disease that can spread from an infected person, animal, or source to another person.
• Innate immunity: Non-specific defense present from birth, including skin, mucus, phagocytes, inflammation, and antimicrobial substances.
• Acquired immunity: Specific protection developed during life after exposure to antigens or vaccination.
• Antigen: A foreign substance that stimulates a specific immune response.
• Antibody: A specific protein produced by B lymphocytes that binds to and helps neutralize a particular antigen.
• B lymphocyte: An immune cell that produces antibodies and forms memory cells during humoral immunity.
• T lymphocyte: An immune cell involved in cell-mediated immunity, including destruction of infected cells and coordination of immune responses.
• Primary immune response: The slower and weaker response produced when the body encounters an antigen for the first time.
• Secondary immune response: A faster and stronger response caused by memory cells during later exposure to the same antigen.
• Vaccine: A preparation containing weakened, killed, or harmless components of a pathogen that stimulates protective immunity.
• Passive immunity: Short-term protection obtained by receiving ready-made antibodies, such as 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.
• Interferons: Proteins released by virus-infected cells that help protect nearby cells from viral infection.
• Malaria: A protozoan disease caused by Plasmodium and transmitted through the bite of an infected female Anopheles mosquito.
• Plasmodium: The malaria-causing parasite whose sexual reproduction occurs in the female Anopheles mosquito.
• Pneumonia: An infection of the lungs, commonly caused by bacteria or viruses, in which the alveoli may fill with fluid.
• Common cold: A viral infection of the nose and upper respiratory tract, commonly caused by rhinoviruses.
• Amoebiasis: An intestinal disease caused by Entamoeba histolytica, often spread through contaminated food or water.
• Ascariasis: A worm infection caused by Ascaris lumbricoides, transmitted through contaminated food, water, or soil.
• Typhoid: A bacterial disease caused by Salmonella typhi and generally spread through contaminated food and water.
• Cancer: A group of diseases characterized by uncontrolled cell division, abnormal growth, and possible invasion of other tissues.
• Oncogene: A gene that can promote uncontrolled cell growth when activated or altered.
• Tumor: An abnormal mass of cells; it may be benign and localized or malignant and invasive.
• Metastasis: The spread of malignant cancer cells from their original site to distant parts of the body.
• Carcinogen: A cancer-causing agent, such as tobacco smoke, certain chemicals, ionizing radiation, or some viruses.
• Benign tumor: A non-cancerous growth that usually remains localized and does not invade nearby tissues.
• Malignant tumor: A cancerous growth that invades surrounding tissues and may spread through blood or lymph.
• HIV: Human immunodeficiency virus, a retrovirus that attacks immune cells, especially CD4-positive helper T cells.
• AIDS: Acquired immunodeficiency syndrome, the advanced condition caused by severe HIV-related weakening of the immune system.
• Reverse transcriptase: An enzyme used by HIV to make DNA from its RNA genetic material.
• ELISA: An antibody-based laboratory test commonly used to detect HIV infection; a positive result requires appropriate confirmatory testing.
• Substance abuse: The harmful or excessive use of substances such as alcohol, tobacco, opioids, cannabinoids, or stimulants.
• Addiction: A strong physical or psychological dependence that makes stopping substance use difficult.
• Withdrawal symptoms: Physical and psychological effects that occur when a dependent person reduces or stops using a substance.
• Opioids: Drugs that act on opioid receptors and may relieve pain but can cause dependence, respiratory depression, and overdose.
• Cannabinoids: Compounds from Cannabis that affect the brain and may alter perception, coordination, memory, and judgment.
• Tobacco dependence: Dependence caused mainly by nicotine, which increases the risk of cardiovascular disease, respiratory disease, and cancer.

Easily Confused

• Innate immunity vs acquired immunity: Innate immunity is non-specific and present from birth, whereas acquired immunity is specific and develops after antigen exposure or vaccination.
• Humoral immunity vs cell-mediated immunity: Humoral immunity is mainly mediated by antibodies produced by B lymphocytes, whereas cell-mediated immunity mainly involves T lymphocytes.
• Primary vs secondary immune response: The primary response is slower and weaker on first exposure; the secondary response is faster and stronger because of memory cells.
• Active vs passive immunity: Active immunity develops through immune activation after infection or vaccination; passive immunity results from receiving ready-made antibodies and is short-term.
• Vaccine vs treatment: Vaccines are preventive and stimulate immune memory; they are not curative.
• Benign vs malignant tumor: A benign tumor usually remains localized, whereas a malignant tumor invades surrounding tissues and may spread.
• Cancer vs metastasis: Cancer is uncontrolled cell growth; metastasis is the spread of malignant cells from the original site to distant parts of the body.
• HIV vs AIDS: HIV is the virus; AIDS is the advanced condition caused by severe HIV-related weakening of the immune system.
• HIV transmission vs casual contact: HIV may be transmitted through unprotected sexual contact, contaminated blood or needles, and infected mother-to-child transmission, but not through handshakes, sharing food, hugging, or mosquito bites.
• Antibiotics vs antiviral treatment: Antibiotics act against susceptible bacteria and do not cure viral diseases such as the common cold.
• Addiction vs withdrawal symptoms: Addiction is dependence on a substance; withdrawal symptoms are the physical and psychological effects of reducing or stopping its use.
• Opioids vs cannabinoids: Opioids act on opioid receptors and may cause respiratory depression and overdose, whereas cannabinoids may alter perception, coordination, memory, and judgment.

What Gets Asked

• Define health, disease, pathogens, communicable disease, innate immunity, acquired immunity, antigens, antibodies, vaccines, HIV, AIDS, cancer, or substance abuse. Marks are lost when health is defined merely as the absence of disease.
• Compare humoral immunity with cell-mediated immunity and explain the roles of B lymphocytes, T lymphocytes, antibodies, and memory cells. Marks are lost when B- and T-lymphocyte functions are interchanged.
• Explain vaccination, primary and secondary immune responses, and passive immunity. Marks are lost when vaccination is described as curative or when passive immunity is treated as long-term immune memory.
• Describe named diseases and their transmission: malaria involves Plasmodium and the infected female Anopheles mosquito; amoebiasis involves Entamoeba histolytica; ascariasis involves Ascaris lumbricoides; and typhoid involves Salmonella typhi. Marks are lost when the pathogen or transmission route is omitted.
• Explain cancer development, tumor types, metastasis, detection, and treatment. Marks are lost when benign tumors are described as invasive or when malignant tumors are not linked to invasion and possible spread.
• Explain HIV transmission, the role of CD4-positive helper T cells and reverse transcriptase, ELISA testing, and antiretroviral therapy. Marks are lost when HIV is said to spread through casual contact or mosquito bites, or when antiretroviral therapy is described as eliminating the virus.
• Explain the effects and prevention of substance abuse. Marks are lost when the effects of alcohol, tobacco, opioids, and cannabinoids are generalized without identifying dependence, organ damage, impaired judgment, respiratory depression, or cancer risk where relevant.