Biology Notes of Chapter 7 Human Health and Disease

This chapter discusses human health, defining it beyond just the absence of disease to encompass physical, mental, and social well-being. Health is influenced by genetic disorders, infections, and lifestyle. Diseases are broadly classified as infectious (transmissible) and non-infectious (like cancer). The chapter details various common infectious diseases caused by bacteria, viruses, protozoans, and helminths, along with their transmission and prevention. Immunity, the body's ability to fight pathogens, is explained through innate (non-specific) and acquired (specific, memory-based) mechanisms, including the roles of antibodies, lymphocytes, and the immune system organs. It also covers allergies, auto-immune diseases, AIDS (a fatal acquired immune deficiency caused by HIV), and cancer (uncontrolled cell growth, metastasis). Finally, it addresses the significant issue of drug and alcohol abuse, especially among youth, highlighting causes, effects, addiction, dependence, and prevention strategies.

Common Diseases in Humans

• Definition of Health: Not just absence of disease or physical fitness. Defined as a state of complete physical, mental and social well-being. Healthy people are more efficient, increasing productivity and economic prosperity. Health increases longevity and reduces infant/maternal mortality.
• Factors Affecting Health:
• Genetic disorders: deficiencies present from birth or inherited.
• Infections.
• Lifestyle: includes food, water, rest, exercise, habits.
• Maintaining Good Health: Balanced diet, personal hygiene, regular exercise. Yoga helps achieve physical and mental health. Awareness about diseases, vaccination, proper waste disposal, vector control, hygiene in food/water are necessary.
• Disease: Occurs when functioning of organs/systems is adversely affected, shown by signs and symptoms.
• Disease Classification:
• Infectious Diseases: Easily transmitted from person to person. Very common. Examples: Typhoid, Pneumonia, Common cold, Malaria, Amoebiasis, Ascariasis, Filariasis, Ringworms. Some are fatal, like AIDS.
• Non-infectious Diseases: Not easily transmitted. Cancer is a major cause of death. Drug and alcohol abuse also affect health adversely.
• Pathogens: Disease-causing organisms (bacteria, viruses, fungi, protozoans, helminths). Most parasites are pathogens.
• Enter body, multiply, interfere with vital activities, causing damage.
• Must adapt to host environment (e.g., survive low pH in stomach).

Specific Infectious Diseases Mentioned:

• Typhoid:
• Caused by: Salmonella typhi (pathogenic bacterium).
• Transmission: Through contaminated food and water. Pathogen enters small intestine, migrates to organs via blood.
• Symptoms: Sustained high fever (39-40°C), weakness, stomach pain, constipation, headache, loss of appetite. Severe cases: intestinal perforation, death.
• Diagnosis: Widal test.
• Classic case: Mary Mallon (Typhoid Mary), a cook who spread typhoid for years as a carrier.
• Pneumonia:
• Caused by: Streptococcus pneumoniae , Haemophilus influenzae (bacteria).
• Infects: Alveoli (air filled sacs) of lungs, filling them with fluid.
• Symptoms: Fever, chills, cough, headache. Severe cases: lips and fingernails turn gray to bluish.
• Transmission: Inhaling droplets/aerosols from infected person, sharing glasses/utensils.
• Other bacterial diseases: Dysentery, plague, diphtheria.
• Common Cold:
• Caused by: Rhino viruses.
• Affects: Nose and respiratory passage (NOT lungs). Most infectious human ailment.
• Symptoms: Nasal congestion/discharge, sore throat, hoarseness, cough, headache, tiredness. Usually lasts 3-7 days.
• Transmission: Inhaling droplets from cough/sneezes, or through contaminated objects (pens, books, doorknobs, etc.).
• Malaria:
• Caused by: Plasmodium (protozoan). Different species cause different types; P. falciparum causes malignant malaria, which can be fatal.
• Life Cycle: Requires two hosts – human and mosquito.
• Enters human as sporozoites (infectious form) via bite of infected female Anopheles mosquito.
• Parasites multiply in liver cells, then attack red blood cells (RBCs).
• RBC rupture releases toxic substance haemozoin, causing recurring chill and high fever every 3-4 days.
• When mosquito bites infected person, parasites enter mosquito, develop into sporozoites stored in salivary glands.
• Mosquito bites human, introduces sporozoites.
• Vector: Female Anopheles mosquito.
• Amoebiasis (Amoebic Dysentery):
• Caused by: Entamoeba histolytica (protozoan parasite in large intestine).
• Symptoms: Constipation, abdominal pain/cramps, stools with excess mucous and blood clots.
• Transmission: Houseflies act as mechanical carriers from infected faeces to food. Main source is contaminated drinking water/food with faecal matter.
• Ascariasis:
• Caused by: Ascaris (common round worm, a helminth intestinal parasite).
• Symptoms: Internal bleeding, muscular pain, fever, anemia, blockage of intestinal passage.
• Transmission: Eggs excreted in faeces contaminate soil, water, plants. Healthy person acquires by contaminated water, vegetables, fruits.
• Elephantiasis or Filariasis:
• Caused by: Wuchereria (filarial worms, e.g., W. bancrofti , W. malayi , helminths).
• Affects: Slowly developing chronic inflammation over years, usually lymphatic vessels of lower limbs. Genital organs also often affected, causing gross deformities.
• Transmission: Bite by female mosquito vectors.
• Ringworms:
• Caused by: Fungi ( Microsporum, Trichophyton, Epidermophyton ). One of the most common infectious skin diseases.
• Symptoms: Dry, scaly lesions on skin, nails, scalp accompanied by intense itching. Fungi thrive in heat/moisture (skin folds).
• Transmission: Acquired from soil or using towels, clothes, comb of infected individuals.

Prevention and Control of Infectious Diseases:

• Personal Hygiene: Keeping body clean, consuming clean food/water/vegetables/fruits.
• Public Hygiene: Proper disposal of waste/excreta, cleaning/disinfecting water reservoirs, hygiene in public catering. Essential for diseases transmitted via food/water (typhoid, amoebiasis, ascariasis).
• Air-borne Diseases (pneumonia, common cold): Avoid close contact with infected persons or belongings.
• Vector-borne Diseases (malaria, filariasis, dengue, chikungunya): Control/eliminate vectors and breeding places.
• Avoid water stagnation around homes.
• Regular cleaning of coolers.
• Use mosquito nets.
• Introduce fish (like Gambusia ) in ponds to eat larvae.
• Spray insecticides in ditches, drainage, swamps.
• Use wire mesh on doors/windows.

Role of Biology:

Advancements in biology have helped control infectious diseases.

• Vaccines and Immunisation: Enabled eradication (smallpox) and control (polio, diphtheria, pneumonia, tetanus) of many diseases. Biotechnology allows newer/safer vaccines.
• Antibiotics and Drugs: Effective treatment for infectious diseases.

Immunity

• Immunity: The body's overall ability to defend itself from disease-causing organisms, conferred by the immune system. Only few exposures result in disease due to this defense.

Types of Immunity:

• Innate Immunity:
• Non-specific type of defense.
• Present at birth.
• Achieved by various barriers to entry of foreign agents.
• Barriers:
• Physical: Skin (main barrier), mucus coating of respiratory, gastrointestinal, urogenital tracts (trap microbes).
• Physiological: Acid in stomach, saliva in mouth, tears from eyes (prevent microbial growth).
• Cellular: Certain leukocytes (WBC) - polymorpho-nuclear leukocytes (PMNL-neutrophils), monocytes, natural killer cells, macrophages (phagocytose and destroy microbes).
• Cytokine: Virus-infected cells secrete interferons (protect non-infected cells from viral infection).
• Acquired Immunity:
• Pathogen specific.
• Characterised by memory .
• First encounter with pathogen: Primary response (low intensity).
• Subsequent encounter with same pathogen: Secondary or Anamnestic response (highly intensified) due to memory of first encounter.
• Mediated by Lymphocytes in blood:
• B-lymphocytes (B-cells): Produce antibodies (proteins) in response to pathogens to fight them.
• T-lymphocytes (T-cells): Do not secrete antibodies but help B-cells produce them. Mediate Cell-Mediated Immunity (CMI).

Antibodies:

• Proteins produced by B-lymphocytes.
• Structure: Four peptide chains - two small (light chains) and two longer (heavy chains). Represented as H₂L₂.
• Types: IgA, IgM, IgE, IgG are some examples.
• Found in blood, hence response is also called Humoral immune response (antibody mediated).

Cell-Mediated Immunity (CMI):

• Mediated by T-lymphocytes.
• Important for distinguishing 'self' and 'non-self'.
• Responsible for graft rejection in organ transplantation. Tissue/blood matching and immunosuppressants are essential for transplants.

Active and Passive Immunity:

• Active Immunity:
• Host is exposed to antigens (living/dead microbes, proteins).
• Antibodies are produced in the host body .
• Slow and takes time for full effect.
• Induced by: Deliberate injection of microbes (immunisation/vaccination) or natural infection.
• Passive Immunity:
• Ready-made antibodies are directly given to protect the body.
• Examples:
• Colostrum (yellowish fluid secreted by mother initially) has abundant IgA antibodies for infant protection.
• Foetus receives some antibodies from mother via placenta.
• Injecting preformed antibodies or antitoxin for quick response (e.g., tetanus, snakebites).

Vaccination and Immunisation:

• Principle: Based on the memory property of the immune system.
• Method: Preparation of antigenic proteins or inactivated/weakened pathogen (vaccine) is introduced.
• Result: Body produces antibodies to neutralise pathogen during actual infection. Vaccines also generate memory B and T-cells for quick, massive antibody production on subsequent exposure.
• Recombinant DNA technology: Allows large-scale production of antigenic polypeptides (e.g., Hepatitis B vaccine from yeast).

Allergies:

• Definition: Exaggerated response of the immune system to certain environmental antigens (allergens).
• Allergens: Substances causing the response (e.g., mites in dust, pollens, animal dander). Sensitivity varies.
• Antibodies: IgE type antibodies are produced.
• Symptoms: Sneezing, watery eyes, running nose, difficulty breathing.
• Cause: Release of chemicals like histamine and serotonin from mast cells.
• Diagnosis: Patient exposed/injected with small doses of possible allergens; reactions studied.
• Treatment: Drugs like anti-histamine, adrenalin, steroids quickly reduce symptoms.
• Modern lifestyle may lower immunity and increase sensitivity to allergens, especially in children in metro cities.

Auto Immunity:

• Basis: Ability of higher vertebrates to differentiate foreign organisms/molecules from self-cells.
• Mechanism: Sometimes, due to genetic/unknown reasons, body attacks self-cells.
• Result: Damage to the body.
• Example: Rheumatoid arthritis.

Immune System Components:

• Consists of: Lymphoid organs, tissues, cells, and soluble molecules (like antibodies).
• Functions: Recognises, responds to, and remembers foreign antigens. Plays role in allergies, auto-immune diseases, organ transplantation.
• Lymphoid Organs:
• Primary Lymphoid Organs: Origin and/or maturation of lymphocytes.
• Bone Marrow: Main lymphoid organ. All blood cells, including lymphocytes, are produced here. Provides micro-environment for B-lymphocyte development/maturation.
• Thymus: Lobed organ near heart, beneath breastbone. Large at birth, reduces with age (puberty). Provides micro-environment for T-lymphocyte maturation.
• Secondary Lymphoid Organs: Sites for lymphocyte interaction with antigen, proliferation to become effector cells.
• Spleen: Large bean-shaped organ. Contains lymphocytes and phagocytes. Filters blood by trapping blood-borne microbes. Large reservoir of erythrocytes.
• Lymph nodes: Small solid structures along lymphatic system. Trap microbes/antigens from lymph/tissue fluid. Antigens activate lymphocytes in nodes, causing immune response.
• Tonsils, Peyer’s patches of small intestine, Appendix.
• Lymphoid Tissue:
• Mucosa-Associated Lymphoid Tissue (MALT): Located within lining of major tracts (respiratory, digestive, urogenital). Constitutes ~50% of lymphoid tissue in human body.

AIDS

• AIDS: Acquired Immuno Deficiency Syndrome.
• Means deficiency of immune system, acquired during lifetime (not congenital).
• 'Syndrome' means a group of symptoms.
• First reported 1981, spread globally.
• Cause: Human Immuno deficiency Virus (HIV).
• A retrovirus with an envelope enclosing RNA genome.
• Transmission: Generally occurs through body fluids.
• Sexual contact with infected person.
• Transfusion of contaminated blood/blood products.
• Sharing infected needles (intravenous drug abusers).
• From infected mother to child through placenta.
• High-Risk Groups: Individuals with multiple sexual partners, intravenous drug addicts, people requiring repeated blood transfusions, children born to HIV-infected mothers.
• Important Note: HIV/AIDS is NOT spread by mere touch or physical contact.
• Time-lag: Between infection and appearance of AIDS symptoms (few months to many years, usually 5-10 years).
• Mechanism of Immune System Deficiency:
• Virus enters body, specifically macrophages.
• Viral RNA genome replicates to viral DNA using enzyme reverse transcriptase.
• Viral DNA incorporates into host cell's DNA, directing cells to produce more virus.
• Macrophages act as HIV factory, producing virus.
• HIV simultaneously enters helper T-lymphocytes (T H).
• Replicates in T H cells, producing progeny viruses that attack other T H cells.
• Progressive decrease in the number of helper T-lymphocytes in the infected person.
• Leads to immuno-deficiency, making the person susceptible to infections that would normally be overcome (e.g., by Mycobacterium , viruses, fungi, Toxoplasma ). Patient cannot protect self against these infections.
• Symptoms: Bouts of fever, diarrhoea, weight loss (due to decreasing T H cells).
• Diagnosis: Enzyme Linked Immuno-Sorbent Assay (ELISA).
• Treatment: Anti-retroviral drugs are only partially effective; they prolong life but cannot prevent inevitable death.
• Prevention: As there is no cure, prevention is the best option. Often spreads due to conscious behaviour patterns. Ignorance is not an excuse.
• Organisations like NACO and NGOs educate people. WHO has programmes.
• Measures: Making blood safe, using only disposable needles/syringes, free condom distribution, controlling drug abuse, advocating safe sex, promoting regular HIV check-ups in susceptible populations.
• Social Aspects: Infection should not be hidden. Infected persons need help and sympathy, not isolation. Tackling AIDS requires collective effort by society and medical fraternity.

Cancer

• Significance: One of the most dreaded diseases and major cause of death globally.
• Mechanism (Cancer cells vs. Normal cells):
• Normal cells: Cell growth and differentiation are highly controlled/regulated. Show contact inhibition (contact with other cells inhibits uncontrolled growth).
• Cancer cells: Breakdown of regulatory mechanisms. Loss of contact inhibition. Continue to divide uncontrollably, forming masses called tumors.
• Tumors:
• Benign Tumors:
• Remain confined to original location.
• Do not spread to other body parts.
• Cause little damage.
• Malignant Tumors:
• Mass of proliferating cells (neoplastic or tumor cells).
• Grow rapidly, invading and damaging surrounding normal tissues.
• Starve normal cells by competing for vital nutrients.
• Cells sloughed off travel via blood to distant sites and start new tumors (metastasis).
• Metastasis is the most feared property of malignant tumors.
• Causes (Carcinogens): Agents inducing transformation of normal to cancerous cells.
• Physical: Ionising radiations (X-rays, gamma rays), non-ionizing radiations (UV) - cause DNA damage.
• Chemical: Present in tobacco smoke (major cause of lung cancer).
• Biological: Oncogenic viruses (contain viral oncogenes). Cellular oncogenes (c-onc) or proto oncogenes in normal cells can be activated to cause transformation.
• Detection and Diagnosis: Early detection is essential for successful treatment.
• Methods:
• Biopsy and histopathological studies: Piece of suspected tissue stained and examined under microscope by pathologist.
• Blood and bone marrow tests: For increased cell counts in leukemias.
• Imaging Techniques:
• Radiography (using X-rays).
• CT (Computed Tomography): Uses X-rays for 3D image of internals.
• MRI (Magnetic Resonance Imaging): Uses strong magnetic fields and non-ionising radiations to detect pathological/physiological changes accurately.
• Antibodies against cancer-specific antigens.
• Molecular Biology Techniques: Detect inherited susceptibility genes; advise avoiding specific carcinogens (e.g., tobacco smoke).
• Treatment: Common approaches are surgery, radiation therapy, and immunotherapy.
• Radiotherapy: Tumor cells irradiated lethally, protecting normal tissue.
• Chemotherapy: Use of drugs to kill cancerous cells; some are tumor-specific. Side effects common (hair loss, anemia).
• Combination Therapy: Most cancers treated by combination of surgery, radiotherapy, chemotherapy.
• Immunotherapy: Use of biological response modifiers (e.g., α-interferon) to activate immune system to destroy tumor cells. Tumor cells can avoid detection/destruction by the immune system.

Drugs and Alcohol Abuse

• Concern: Rising use, especially among youth. Proper education/guidance needed.
• Common Abused Drugs: Opioids, cannabinoids, coca alkaloids. Mostly from flowering plants, some from fungi.

Opioids:

• Bind to specific opioid receptors in CNS and GI tract.
• Example: Heroin (smack), chemically diacetylmorphine. White, odourless, bitter crystalline.
• Source: Obtained by acetylation of morphine, extracted from latex of poppy plant Papaver somniferum .
• Consumption: Snorting and injection.
• Effect: Depressant, slows down body functions.

Cannabinoids:

• Bind to cannabinoid receptors, principally in the brain.
• Source: Natural cannabinoids from inflorescences of Cannabis sativa .
• Products: Marijuana, hashish, charas, ganja (various combinations of flower tops, leaves, resin).
• Consumption: Inhalation and oral ingestion.
• Effect: Known effects on cardiovascular system. Abused by sportspersons.

Coca Alkaloid (Cocaine):

• Cocaine (coke or crack).
• Source: Coca plant Erythroxylum coca (native to South America).
• Mechanism: Interferes with dopamine neurotransmitter transport.
• Consumption: Usually snorted.
• Effect: Potent CNS stimulant, produces euphoria, increased energy. Excessive dosage causes hallucinations.
• Other Hallucinogenic Plants: Atropa belladona , Datura .
• Other Abused Drugs: Barbiturates, amphetamines, benzodiazepines (normally used as medicines for mental illness, insomnia).
• Morphine: Effective sedative and painkiller, useful post-surgery.
• Definition of Drug Abuse: Taking drugs for purpose other than medicinal use, or in amounts/frequency impairing physical, physiological, or psychological functions.

Smoking (Tobacco):

• Contains nicotine (an alkaloid).
• Nicotine stimulates adrenal gland to release adrenaline/nor-adrenaline, raising blood pressure and heart rate.
• Associated with increased incidence of: Lung, urinary bladder, throat cancers, bronchitis, emphysema, coronary heart disease, gastric ulcer. Tobacco chewing associated with oral cavity cancer.
• Increases blood CO content, reducing oxygen bound to haemoglobin, causing oxygen deficiency.
• Has statutory warning, but still prevalent. Addictive nature. Addicts need counselling/medical help. Smoking can pave the way to hard drugs.

Adolescence and Abuse:

• Adolescence (approx. 12-18 years): Period of maturation, vulnerable phase of mental/psychological development.
• Motivations for abuse in youngsters:
• Curiosity, need for adventure/excitement, experimentation.
• Perceived benefits, escape problems.
• Stress from academic/examination pressures.
• Perception that it's 'cool' or progressive (media influence).
• Unstable/unsupportive family structures.
• Peer pressure.

Addiction and Dependence:

• Repeated use leads to addiction.
• Addiction: Psychological attachment to certain effects (euphoria, well-being). Drives continued use even when self-destructive.
• Tolerance increases with repeated use, requiring higher doses, leading to greater intake/addiction. First use can lead to addiction. Vicious circle. Without guidance, leads to addiction and dependence.
• Dependence: Body's tendency to show unpleasant withdrawal syndrome if regular dose is stopped abruptly.
• Withdrawal symptoms: Anxiety, shakiness, nausea, sweating. Relieved by resuming use. Can be severe, even life-threatening, requiring medical supervision.
• Dependence leads to ignoring social norms for funds, causing social adjustment problems.

Effects of Drug/Alcohol Abuse:

• Immediate adverse effects: Reckless behaviour, vandalism, violence.
• Excessive doses: Coma, death (respiratory failure, heart failure, cerebral hemorrhage). Combination with alcohol/other drugs leads to overdose/death.
• Warning signs in youth: Drop in academics, unexplained absence, poor hygiene, withdrawal, isolation, depression, fatigue, aggression, rebellious behaviour, poor relationships, loss of hobbies, changes in sleep/eating, weight/appetite fluctuations.
• Far-reaching implications: Stealing for money. Mental/financial distress to family/friends.
• Increased risk of serious infections: AIDS and Hepatitis B (especially via shared needles by intravenous drug users). Viruses transmitted by shared needles, sexual contact, or infected blood. Both infections are chronic and ultimately fatal.
• Long-term effects: Adolescent alcohol use can lead to heavy drinking in adulthood. Chronic use damages nervous system and liver (cirrhosis). Use during pregnancy adversely affects fetus.
• Misuse by Sportspersons: To enhance performance (anabolic steroids, etc.).
• Side effects (Anabolic Steroids):
• Females: masculinisation, aggressiveness, mood swings, depression, abnormal cycles, excessive facial/body hair, clitoris enlargement, deep voice.
• Males: acne, aggressiveness, mood swings, depression, reduced testicle size, decreased sperm, potential kidney/liver dysfunction, breast enlargement, premature baldness, prostate gland enlargement.
• Effects can be permanent with prolonged use.
• Adolescents (male/female): Severe facial/body acne, premature closure of long bone growth centres potentially leading to stunted growth.

Prevention and Control:

'Prevention is better than cure'. Habits start young, often in adolescence.

• Identify situations pushing adolescents towards abuse; take remedial measures early.
• Parents and teachers have special responsibility. Parenting with nurture and consistent discipline lowers risk.
• Specific Measures:
• Avoid undue peer pressure: Respect child's choice/personality; don't push beyond limits (studies, sports, etc.).
• Education and counselling: Teach how to face problems/stress, accept disappointments/failures. Channel energy into healthy pursuits (sports, reading, music, yoga, extracurriculars).
• Seeking help from parents/peers: Seek help immediately for guidance; vent feelings of anxiety/guilt with trusted friends.
• Looking for danger signs: Alert parents/teachers/friends identify danger signs; bring concerns to notice of parents/teachers for proper diagnosis/treatment.
• Seeking professional and medical help: Qualified psychologists, psychiatrists, de-addiction, rehabilitation programs available. With help, effort, willpower, individuals can overcome problem.

Frequently Asked Questions:

1. What is health according to the source?
   
   Health is defined as a state of complete physical, mental, and social well-being, not merely the absence of disease or physical fitness. Being healthy increases efficiency, productivity, longevity, and reduces mortality.
2. How does the body defend itself against pathogens?
   
   The body has an immune system providing immunity, the ability to fight disease-causing organisms. This includes innate immunity (non-specific barriers like skin, physiological secretions, and phagocytic cells) and acquired immunity (specific, memory-based response involving lymphocytes that produce antibodies or mediate cell-based killing).
   
   
3. What are the main ways HIV is transmitted?
   
   HIV is primarily transmitted through body fluids via sexual contact with an infected person, transfusion of contaminated blood or blood products, sharing infected needles among intravenous drug abusers, and from an infected mother to her child through the placenta.