Biology: Class 12 — Chapter 7: Human Health and Disease

• Typhoid Fever: Caused by the bacterium Salmonella typhi. It enters the small intestine through contaminated food/water and migrates via blood. Symptoms include sustained high fever (39° to 40°C), weakness, stomach pain, constipation, headache, and loss of appetite. Intestinal perforation and death may occur in severe cases. Confirmed by the Widal test. A classic carrier case is Mary Mallon ("Typhoid Mary").
• Pneumonia: Caused by Streptococcus pneumoniae and Haemophilus influenzae. It infects the alveoli of the lungs, filling them with fluid and leading to respiratory issues. Symptoms include fever, chills, cough, headache, and gray-to-blue lips/fingernails. Transmitted by inhaling droplets/aerosols or sharing utensils.
• Other Bacterial Diseases: Dysentery, plague, and diphtheria.

• Common Cold: Caused by Rhino viruses. They infect the nose and respiratory passage but not the lungs. Symptoms include nasal congestion, discharge, sore throat, hoarseness, cough, headache, and tiredness (lasting 3-7 days). Transmitted via droplets or contaminated objects (pens, books, doorknobs).

• Malaria: Caused by Plasmodium species (P. vivax, P. malaria, and P. falciparum). Malignant malaria caused by P. falciparum is the most serious and fatal. Let us trace the life cycle of the parasite:
  1. Infectious stage (sporozoites) enters the human body through the bite of an infected female Anopheles mosquito.
  2. Parasites multiply within liver cells, then attack red blood cells (RBCs), causing them to rupture.
  3. Rupture of RBCs releases a toxic substance, haemozoin, which causes recurring chills and high fever every 3-4 days.
  4. Female Anopheles mosquito bites an infected person, taking up gametocytes.
  5. Fertilization and development take place in the mosquito's gut; mature sporozoites migrate to salivary glands.
• Amoebiasis (Amoebic Dysentery): Caused by the protozoan parasite Entamoeba histolytica in the large intestine. Symptoms include constipation, abdominal pain, cramps, and stools with excess mucus and blood clots. Houseflies act as mechanical carriers to contaminate food and water.

• Ascariasis: Caused by the intestinal roundworm parasite Ascaris. Symptoms include internal bleeding, muscular pain, fever, anemia, and blockage of the intestinal passage. Eggs are excreted with feces, contaminating soil, water, and plants.
• Elephantiasis / Filariasis: Caused by filarial worms Wuchereria bancrofti and W. malayi. It causes chronic inflammation of the lymphatic vessels of the lower limbs and genital organs, leading to gross deformities. Transmitted by female mosquito vectors.

• Ringworms: Caused by fungi belonging to genera Microsporum, Trichophyton, and Epidermophyton. Symptoms include dry, scaly lesions on skin, nails, and scalp, accompanied by intense itching. Heat and moisture help these fungi thrive in skin folds (groin, toes).

• Personal Hygiene: Keeping the body clean, consuming clean drinking water, food, vegetables, and fruits.
• Public Hygiene: Proper disposal of waste/excreta, periodic cleaning/disinfection of water reservoirs, pools, and tanks.
• Vector Control: Eliminating breeding places, avoiding stagnant water, regular cleaning of coolers, using mosquito nets, introducing larvivorous fish like Gambusia in ponds, spraying insecticides, and installing wire mesh on doors/windows. Essential for preventing vector-borne diseases like malaria, filariasis, dengue, and chikungunya (transmitted by Aedes mosquitoes).
• Immunisation: Use of vaccines has helped eradicate smallpox and control polio, diphtheria, pneumonia, and tetanus.

Non-specific type of defense present at the time of birth, consisting of four barriers:

• Physical barriers: Skin (prevents entry of microbes) and mucus coating of respiratory, gastrointestinal, and urogenital tracts.
• Physiological barriers: Acid in the stomach, saliva in the mouth, and tears from the eyes.
• Cellular barriers: Leukocytes like polymorpho-nuclear leukocytes (PMNL-neutrophils), monocytes, natural killer cells, and macrophages in tissues.
• Cytokine barriers: Virus-infected cells secrete proteins called interferons, which protect non-infected cells from further viral infection.

Pathogen-specific immunity characterized by memory. It involves two types of lymphocytes:

• B-lymphocytes: Produce proteins called antibodies into the blood to fight pathogens (Humoral immune response).
• T-lymphocytes: Do not secrete antibodies but help B-cells produce them. They mediate the cell-mediated immunity (CMI), which is responsible for graft rejection during organ transplantation.

Antibody Structure: Each antibody molecule has four peptide chains: two small light chains and two longer heavy chains, represented as $H_2L_2$. Types include IgA, IgM, IgE, and IgG.

• Active Immunity: Produced when a host is exposed to antigens (living/dead microbes or proteins). It is slow and takes time to give a full response.
• Passive Immunity: Readily prepared antibodies are directly given to protect the body. Examples: colostrum (yellowish fluid secreted by mother during initial days of lactation containing abundant IgA antibodies) and antibodies received by the fetus through the placenta.

Based on the property of 'memory' of the immune system. In vaccination, antigenic proteins or inactivated pathogens are introduced, generating antibodies and memory B and T-cells. Recombinant DNA technology allows large-scale production of vaccines (e.g., Hepatitis B vaccine from yeast).

Passive Immunisation: Direct injection of preformed antibodies or antitoxins (e.g., for tetanus or snakebites) when a quick immune response is required.

• Allergies: Exaggerated response of the immune system to environmental antigens (allergens like pollen, mites, dander). Mediated by IgE antibodies and release of histamine and serotonin from mast cells. Treated with anti-histamines, adrenalin, and steroids.
• Auto Immunity: When the body attacks its own self-cells due to genetic or unknown reasons (e.g., Rheumatoid arthritis).
• Lymphoid Organs:
  • Primary: Bone marrow and thymus (where lymphocytes mature and differentiate).
  • Secondary: Spleen, lymph nodes, tonsils, Peyer's patches of small intestine, and appendix (sites for interaction with antigens).
  • MALT: Mucosa-associated lymphoid tissue constitutes about 50% of lymphoid tissue in the human body, lining major tracts.

• Opioids: Bind to specific receptors in the CNS and gastrointestinal tract. Example: Heroin (smack / diacetylmorphine), extracted from the latex of the poppy plant Papaver somniferum. It is a depressant that slows down body functions.
• Cannabinoids: Interact with cannabinoid receptors in the brain. Obtained from inflorescences of Cannabis sativa (marijuana, hashish, charas, ganja). Affect the cardiovascular system.
• Coca Alkaloids / Cocaine: Obtained from Erythroxylum coca. It interferes with dopamine transport, producing euphoria and increased energy. Excessive dosage causes hallucinations.
• Hallucinogens: Obtained from plants like Atropa belladona and Datura.
• Other Abused Drugs: Barbiturates, amphetamines, and benzodiazepines (used medically to treat depression/insomnia). Morphine is used medically as a sedative and painkiller.
• Tobacco: Contains nicotine, which stimulates adrenal glands to release adrenaline and nor-adrenaline, raising blood pressure and heart rate. Smoking is associated with lung, urinary bladder, and throat cancers, bronchitis, emphysema, and coronary heart disease.

• Addiction: Psychological attachment to effects like euphoria and temporary well-being. Repeated use increases tolerance levels of receptors, leading to higher consumption.
• Dependence: Tendency of the body to manifest an unpleasant withdrawal syndrome (anxiety, shakiness, nausea, sweating) if drug/alcohol use is abruptly discontinued.
• Effects of Abuse: Reckless behavior, vandalism, violence, coma, and death due to respiratory/heart failure or cerebral hemorrhage. Chronic use causes damage to the nervous system and liver (cirrhosis).
• Anabolic Steroids Side-Effects:
  • In Females: Masculinisation, aggressiveness, mood swings, abnormal menstrual cycles, excessive hair growth, and deepening of voice.
  • In Males: Acne, aggressiveness, mood swings, reduction of testicle size, decreased sperm production, breast enlargement, and premature baldness.

1. Avoid undue peer pressure.
2. Education and counselling to face problems and accept disappointments.
3. Seeking help from parents and peers.
4. Looking for danger signs of abuse.
5. Seeking professional and medical help (psychologists, psychiatrists, and de-addiction programs).