Human Health and Disease — Notes

Health is a state of complete physical, mental and social well-being. It is affected by genetic disorders, infections and lifestyle (food and water, rest and exercise, habits). Disease-causing organisms are pathogens.

Plasmodium needs two hosts. Female Anopheles injects sporozoites → multiply in liver cells → attack RBCs, multiply, burst them (haemozoin: chill and fever every 3–4 days) → gametocytes form in RBCs → taken up by a female Anopheles → fertilisation and development in the mosquito's stomach wall → sporozoites stored in the salivary glands → injected at the next bite.

Prevention and control:

• Personal hygiene: clean body; safe drinking water, food, vegetables and fruits.
• Public hygiene: proper disposal of waste and excreta; periodic cleaning and disinfection of water reservoirs, pools, cesspools and tanks; standard practices in public catering.
• Air-borne diseases: avoid close contact with infected persons and their belongings.
• Vector-borne diseases (malaria, filariasis, dengue, chikungunya): avoid stagnant water near homes; clean household coolers regularly; use mosquito nets; introduce Gambusia fish that feed on mosquito larvae; spray insecticides in ditches, drainage areas and swamps; fit wire mesh on doors and windows.
• Vaccination and modern medicines have controlled many diseases; smallpox has been eradicated.

Innate immunity (non-specific, present at birth): physical barriers (skin, mucus of respiratory, gastrointestinal and urogenital tracts); physiological (stomach acid, saliva, tears); cellular (PMNL-neutrophils, monocytes, natural killer lymphocytes, macrophages); cytokine (interferons from virus-infected cells).

Acquired immunity (pathogen-specific, with memory): primary response of low intensity; secondary (anamnestic) response highly intensified. B-lymphocytes produce antibodies (humoral immunity); T-lymphocytes help B cells and mediate cell-mediated immunity (CMI), which is responsible for graft rejection (hence tissue and blood-group matching and immunosuppressants).

Antibody: four polypeptide chains, two heavy and two light (H₂L₂); IgA, IgM, IgE, IgG.

Active immunity: the host makes antibodies after exposure to antigens (infection or vaccine); slow, long-lasting. Passive immunity: ready-made antibodies given — colostrum (IgA), antibodies through the placenta, anti-tetanus serum, snake antivenom; quick, short-lived.

Vaccination: antigenic proteins or inactivated/weakened pathogens produce memory B and T cells; a later exposure gives a rapid, massive response. Recombinant DNA technology allows antigens to be produced in bacteria or yeast (hepatitis B vaccine from yeast).

Allergy: exaggerated response to allergens (dust mites, pollen, animal dander); IgE; mast cells release histamine and serotonin; treated with anti-histamines, adrenalin, steroids. Autoimmunity: attack on self cells, e.g. rheumatoid arthritis.

Lymphoid organs: primary — bone marrow, thymus; secondary — spleen, lymph nodes, tonsils, Peyer's patches, appendix; MALT forms about half the lymphoid tissue.

AIDS (Acquired Immuno Deficiency Syndrome), first reported in 1981, is caused by HIV, a retrovirus with an RNA genome. Transmission: sexual contact with an infected person; transfusion of contaminated blood or blood products; sharing infected needles; infected mother to child through the placenta. Not by casual contact. Time lag of 5–10 years from infection to symptoms.

How it acts: HIV enters macrophages; RNA → viral DNA by reverse transcriptase; viral DNA incorporated into host DNA; infected cells make virus particles (macrophage as an HIV factory); HIV enters helper T-lymphocytes, replicates and destroys them; their number falls; immunodeficiency leads to opportunistic infections (Mycobacterium, viruses, fungi, Toxoplasma).

Diagnosis: ELISA. Treatment: antiretroviral drugs (partly effective; prolong life). Prevention: NACO and other organisations; disposable needles and syringes; screening of blood; condoms and safe practices; control of drug abuse; regular check-ups for susceptible groups; awareness and acceptance rather than stigma.

Normal cells show contact inhibition; cancer cells lose it and divide uncontrollably, forming tumours. Benign tumours stay confined and cause little damage. Malignant tumours grow rapidly, invade surrounding tissues and spread to distant sites through blood (metastasis).

Causes (carcinogens): physical — ionising radiations (X-rays, gamma rays) and non-ionising UV; chemical — tobacco smoke (major cause of lung cancer); biological — oncogenic viruses with viral oncogenes. Cellular oncogenes (c-onc, proto-oncogenes) in normal cells can be activated and cause cancer.

Detection: biopsy and histopathology; blood and bone marrow tests (leukaemia); radiography, CT (computed tomography) and MRI (magnetic resonance imaging); antibodies against cancer-specific antigens; molecular techniques to detect genes for inherited susceptibility.

Treatment: surgery, radiation therapy, chemotherapy (side effects such as hair loss and anaemia), immunotherapy with biological response modifiers such as α-interferon; usually a combination.

Commonly abused drugs:

• Opioids bind opioid receptors in the CNS and gut. Heroin (smack, diacetylmorphine) is made by acetylation of morphine from the latex of the poppy (Papaver somniferum); a depressant that slows body functions.
• Cannabinoids (marijuana, hashish, charas, ganja) from Cannabis sativa; affect the cardiovascular system.
• Cocaine from Erythroxylum coca; interferes with dopamine transport; stimulation and euphoria; excessive doses cause hallucinations. Other hallucinogens: Atropa belladonna, Datura. Medicines such as barbiturates, amphetamines and benzodiazepines are also misused.

Tobacco: nicotine stimulates the adrenal gland to release adrenaline and nor-adrenaline, raising blood pressure and heart rate. Smoking causes cancers of lung, urinary bladder and throat, bronchitis, emphysema, coronary heart disease and gastric ulcer; CO reduces oxygen bound to haemoglobin. Chewing tobacco causes oral cancer.

Adolescence (12–18 years): curiosity, adventure, experimentation, stress, peer pressure, media. Repeated use → addiction and dependence, with a withdrawal syndrome (anxiety, shakiness, nausea, sweating). Effects: reckless behaviour, vandalism, violence; overdose may cause coma and death; shared needles spread HIV and hepatitis B; chronic alcohol damages the nervous system and liver (cirrhosis) and harms the foetus. Misuse of anabolic steroids in sport causes hormonal and organ damage.

Prevention: avoid undue peer pressure; education and counselling; help from parents and peers; looking for danger signs; professional and medical help (de-addiction and rehabilitation).