Human Health and Disease notes

This chapter connects health, disease, immunity, infection, cancer and substance abuse into one NEET-important framework. Health is not only absence of disease but physical, mental and social well-being. Diseases may be infectious, caused by pathogens such as bacteria, viruses, protozoans and helminths, or non-infectious, such as cancer and lifestyle disorders. NCERT strongly emphasizes common human diseases like typhoid, pneumonia, common cold, malaria, amoebiasis, ascariasis and filariasis. Immunity protects the body through innate barriers and acquired responses mediated by B cells, T cells and antibodies. Vaccination uses immunological memory. AIDS, cancer and drug abuse are high-yield topics because they combine causation, symptoms, prevention, diagnosis and social awareness.

Pathogens are disease-causing organisms such as bacteria, viruses, protozoans and helminths. Infectious diseases spread through direct contact, droplets, contaminated food and water, vectors, sexual contact or blood. NCERT emphasizes specific pathogen-disease pairs: Salmonella typhi causes typhoid, Streptococcus pneumoniae and Haemophilus influenzae cause pneumonia, rhinoviruses cause common cold, Plasmodium causes malaria, Entamoeba histolytica causes amoebiasis, Ascaris causes ascariasis and Wuchereria causes filariasis. NEET often asks symptoms, body sites affected and transmission routes. Understanding life cycles is crucial, especially malaria, where female Anopheles mosquito acts as vector and Plasmodium alternates between human liver, red blood cells and mosquito gut.

Immunity is the ability of the body to fight disease-causing organisms and foreign substances. Innate immunity is present from birth and acts non-specifically through physical, physiological, cellular and cytokine barriers. Acquired immunity develops after exposure to a specific antigen and shows specificity and memory. It has two major arms: humoral immunity, mediated by antibodies produced by B lymphocytes, and cell-mediated immunity, mediated mainly by T lymphocytes. Antibodies are Y-shaped immunoglobulins with two heavy and two light chains. Vaccination introduces harmless antigenic material to produce memory B and T cells, causing a faster secondary response. Allergies are exaggerated immune responses, while autoimmune disorders occur when immunity attacks self tissues.

AIDS stands for Acquired Immuno Deficiency Syndrome and is caused by HIV, a retrovirus. HIV has an envelope, RNA genome and the enzyme reverse transcriptase. The virus mainly attacks helper T lymphocytes, especially CD4 cells, weakening cell-mediated immunity. HIV spreads through sexual contact with an infected person, transfusion of contaminated blood, sharing infected needles and from infected mother to child through placenta or breast milk. It does not spread by hugging, sharing food, mosquito bite or casual contact. After infection, HIV may remain clinically silent for years while CD4 count declines. Diagnosis is commonly by ELISA, and prevention depends on safe sex, screened blood, sterile needles and public awareness.

Cancer is a disease in which normal cells lose growth control and divide continuously to form tumours. Tumours may be benign, remaining localized, or malignant, invading surrounding tissues and spreading to distant organs by metastasis. Cancer cells show loss of contact inhibition, rapid proliferation, ability to evade immune destruction and abnormal metabolism. Causes include physical carcinogens such as ionising radiations and UV rays, chemical carcinogens such as tobacco smoke components, biological agents such as oncogenic viruses and genetic changes activating oncogenes. Detection uses biopsy, histopathology, blood and bone marrow tests, radiography, CT, MRI and antibodies against cancer-specific antigens. Treatment includes surgery, radiotherapy, chemotherapy and immunotherapy using biological response modifiers.

Drug, alcohol and tobacco abuse refers to harmful use of substances that alter body and mind. NCERT highlights opioids, cannabinoids and cocaine. Opioids such as morphine and heroin bind to opioid receptors and depress body functions. Cannabinoids from Cannabis affect the cardiovascular system and brain. Cocaine from Erythroxylum coca interferes with dopamine transport and produces euphoria and increased energy, but overdose can cause hallucinations and damage. Alcohol abuse damages liver, nervous system and social life. Tobacco smoking exposes the body to nicotine, tar, carbon monoxide and carcinogens, increasing risk of cancer, bronchitis, emphysema and heart disease. Prevention involves education, family support, counselling, peer resistance and medical help.