Human Health and DiseaseClass 12 Biology Notes

HUMAN HEALTH AND DISEASE

Defining Health and Disease

For a long time, health was thought to be a balance of body fluids or 'humors', an idea proposed by early Greeks like Hippocrates and the Indian Ayurveda system. This was called the 'good humor' hypothesis. However, the discovery of blood circulation by William Harvey, using experimental methods, disproved this idea.

Today, we understand that our mind and mental state can influence our health through the nervous and endocrine systems, which in turn affect our immune system.

Health is not merely the absence of disease or physical fitness. It is a state of complete physical, mental, and social well-being.

A healthy person is more efficient, productive, and generally lives longer. Good health helps reduce infant and maternal mortality rates.

Factors Affecting Health:

• Genetic Disorders: Defects or deficiencies a child is born with or inherits.
• Infections: Diseases caused by pathogens.
• Life Style: The food and water we consume, the rest and exercise we get, and our personal habits.

A disease is a condition where the functioning of one or more organs or systems of the body is negatively affected, leading to various signs and symptoms.

Types of Diseases:

• Infectious Diseases: Easily transmitted from one person to another (e.g., common cold, AIDS).
• Non-infectious Diseases: Cannot be transmitted from person to person (e.g., cancer, genetic disorders).

Common Diseases in Humans

Disease-causing organisms are called pathogens. These can be bacteria, viruses, fungi, protozoans, or helminths. Pathogens must adapt to survive inside the host's body, for example, by resisting stomach acid.

Bacterial Diseases

• Typhoid Fever

  • Pathogen: Salmonella typhi (bacterium).
  • Transmission: Enters the small intestine through contaminated food and water.
  • Symptoms: Sustained high fever ($39^{\circ}$ to $40^{\circ} \mathrm{C}$), weakness, stomach pain, constipation, headache, and loss of appetite. In severe cases, it can cause intestinal perforation and death.
  • Diagnosis: Confirmed by the Widal test. [!example] Typhoid Mary: A famous case in medicine involves Mary Mallon, a cook who was a typhoid carrier. She unknowingly spread the disease for years through the food she prepared.

• Pneumonia

  • Pathogens: Streptococcus pneumoniae and Haemophilus influenzae.
  • Target Organ: Infects the alveoli (air sacs) of the lungs, causing them to fill with fluid.
  • Symptoms: Fever, chills, cough, and headache. In severe cases, lips and fingernails may turn grey or bluish.
  • Transmission: Inhaling droplets/aerosols from an infected person or sharing their utensils.

Other bacterial diseases include dysentery, plague, and diphtheria.

Viral Diseases

• Common Cold
  • Pathogen: Rhino viruses.
  • Target Area: Infects the nose and respiratory passage, but not the lungs.
  • Symptoms: Nasal congestion and discharge, sore throat, cough, headache, and tiredness. Usually lasts 3-7 days.
  • Transmission: Inhaling droplets from a cough or sneeze, or touching contaminated objects (pens, doorknobs, keyboards).

Protozoan Diseases

• Malaria

  • Pathogen: Plasmodium (a tiny protozoan). Different species (P. vivax, P. malariae, P. falciparum) cause different types of malaria. Malignant malaria, caused by P. falciparum, is the most serious and can be fatal.
  • Vector: Transmitted by the bite of an infected female Anopheles mosquito.
  • Life Cycle:
    1. The mosquito injects sporozoites (infectious form) into a human.
    2. Parasites multiply in the liver cells and then attack red blood cells (RBCs).
    3. The rupture of RBCs releases a toxin called haemozoin, which causes recurring chills and high fever every 3-4 days.
    4. A mosquito bites an infected person, ingesting the parasites.
    5. The parasites develop and multiply inside the mosquito, forming sporozoites that are stored in its salivary glands, ready to infect another human. [!note] The malarial parasite requires two hosts to complete its life cycle: humans and mosquitoes.

• Amoebiasis (Amoebic Dysentery)

  • Pathogen: Entamoeba histolytica (a protozoan parasite in the large intestine).
  • Symptoms: Constipation, abdominal pain, cramps, and stools with excess mucous and blood clots.
  • Transmission: Houseflies act as mechanical carriers, transferring the parasite from the feces of an infected person to food. The main source of infection is drinking water and food contaminated by fecal matter.

Helminthic Diseases (Diseases caused by worms)

• Ascariasis

  • Pathogen: Ascaris (the common roundworm), an intestinal parasite.
  • Symptoms: Internal bleeding, muscular pain, fever, anemia, and blockage of the intestinal passage.
  • Transmission: A healthy person gets infected through contaminated water, vegetables, and fruits containing the parasite's eggs, which are excreted in the feces of an infected person.

• Elephantiasis (Filariasis)

  • Pathogen: Wuchereria (W. bancrofti and W. malayi), the filarial worms.
  • Symptoms: A slowly developing chronic inflammation of the organs where the worms live, usually the lymphatic vessels of the lower limbs, causing gross deformities. Genital organs are also often affected.
  • Transmission: Bite of female mosquito vectors.

Fungal Diseases

• Ringworms
  • Pathogens: Fungi from the genera Microsporum, Trichophyton, and Epidermophyton.
  • Symptoms: Appearance of dry, scaly lesions on the skin, nails, and scalp, accompanied by intense itching.
  • Growth Conditions: Heat and moisture help these fungi grow, so they thrive in skin folds like the groin or between the toes.
  • Transmission: Acquired from soil or by sharing towels, clothes, or combs of infected individuals.

Prevention and Control of Infectious Diseases

• Personal Hygiene: Keeping the body clean, consuming clean drinking water, food, vegetables, and fruits.
• Public Hygiene: Proper disposal of waste and excreta, periodic cleaning of water reservoirs, and observing hygiene in public catering.
• For Air-borne diseases (Pneumonia, Common Cold): Avoid close contact with infected persons and their belongings.
• For Vector-borne diseases (Malaria, Filariasis):
  • Control or eliminate vectors and their breeding places.
  • Avoid water stagnation.
  • Regularly clean household coolers.
  • Use mosquito nets.
  • Introduce larvae-eating fish like Gambusia in ponds.
  • Spray insecticides in ditches and drainage areas.
  • Use wire mesh on doors and windows.

Immunity

Immunity is the overall ability of the body to fight disease-causing organisms, which is conferred by the immune system.

Innate Immunity

This is a non-specific type of defense that is present from birth. It consists of four types of barriers:

1. Physical Barriers:
   • Skin: The main barrier preventing the entry of microbes.
   • Mucus Coating: The epithelium lining the respiratory, gastrointestinal, and urogenital tracts traps microbes.
2. Physiological Barriers:
   • Acid in the stomach.
   • Saliva in the mouth.
   • Tears from the eyes. All of these prevent microbial growth.
3. Cellular Barriers:
   • Certain white blood cells (leukocytes) like neutrophils (PMNL) and monocytes.
   • Natural killer cells (a type of lymphocyte).
   • Macrophages in tissues. These cells can phagocytose (engulf) and destroy microbes.
4. Cytokine Barriers:
   • Virus-infected cells secrete proteins called interferons, which protect non-infected cells from further viral infection.

Acquired Immunity

This type of immunity is pathogen-specific and is characterized by memory.

• Primary Response: The body's first encounter with a pathogen produces a response of low intensity.
• Secondary (Anamnestic) Response: A subsequent encounter with the same pathogen triggers a highly intensified response because the immune system "remembers" the first encounter.

This memory is due to two special types of lymphocytes: B-lymphocytes and T-lymphocytes.

• Humoral Immune Response (Antibody-Mediated):

  • B-lymphocytes produce an army of proteins called antibodies in response to pathogens.
  • Antibodies are found in the blood. An antibody molecule has four peptide chains: two small light chains and two longer heavy chains, represented as $\mathrm{H}_{2} \mathrm{~L}_{2}$.
  • Examples of antibodies include IgA, IgM, IgE, IgG.

• Cell-Mediated Immune Response (CMI):

  • This response is mediated by T-lymphocytes. T-cells do not secrete antibodies but help B-cells produce them.
  • CMI is responsible for graft rejection during organ transplants. The body can differentiate between 'self' and 'non-self' cells, which is why tissue and blood group matching are essential before a transplant. Patients must take immunosuppressants for life to prevent rejection.

Active and Passive Immunity

• Active Immunity:

  • The body produces its own antibodies when exposed to antigens (living or dead microbes or other proteins).
  • This process is slow but gives a full and effective response.
  • It is induced naturally during an infection or deliberately during immunisation (vaccination).

• Passive Immunity:

  • Ready-made antibodies are given directly to the body for quick protection.
  • Examples:
    • The yellowish fluid colostrum, secreted by the mother during the initial days of lactation, is rich in IgA antibodies and protects the infant.
    • A fetus receives antibodies from the mother through the placenta during pregnancy.

Vaccination and Immunisation

The principle of vaccination is based on the memory of the immune system.

• A vaccine is a preparation of antigenic proteins of a pathogen or an inactivated/weakened pathogen.
• When introduced into the body, the vaccine stimulates the production of antibodies and memory B- and T-cells.
• These memory cells recognize the pathogen quickly during a real infection and overwhelm it with a massive production of antibodies.
• Passive Immunisation: In cases where a quick immune response is needed (like tetanus or snakebite), preformed antibodies or antitoxin are directly injected.
• Recombinant DNA Technology: This has allowed for the large-scale production of safer vaccines, such as the hepatitis B vaccine produced from yeast.

Allergies

An allergy is the exaggerated response of the immune system to certain antigens (called allergens) present in the environment.

• Common Allergens: Mites in dust, pollens, animal dander.
• Antibody Involved: IgE type.
• Symptoms: Sneezing, watery eyes, running nose, difficulty in breathing.
• Cause: Release of chemicals like histamine and serotonin from mast cells.
• Treatment: Use of drugs like anti-histamines, adrenaline, and steroids.

Autoimmunity

Sometimes, due to genetic or other unknown reasons, the body attacks its own cells. This is called an auto-immune disease.

• Example: Rheumatoid arthritis.

Immune System in the Body

The human immune system consists of lymphoid organs, tissues, cells, and antibodies.

• Lymphoid Organs: These are where lymphocytes originate, mature, and proliferate.
  • Primary Lymphoid Organs: This is where immature lymphocytes differentiate into antigen-sensitive lymphocytes.
    • Bone Marrow: The main lymphoid organ where all blood cells, including lymphocytes, are produced.
    • Thymus: A lobed organ near the heart, large at birth but reduces in size with age. It's the site for the development and maturation of T-lymphocytes.
  • Secondary Lymphoid Organs: These provide the sites for lymphocytes to interact with antigens.
    • Spleen: A large, bean-shaped organ that filters blood by trapping blood-borne microorganisms. It contains lymphocytes and phagocytes.
    • Lymph Nodes: Small structures along the lymphatic system that trap microbes or antigens from the lymph and tissue fluid, activating lymphocytes.
    • Tonsils, Peyer's patches of the small intestine, and the appendix.
• Mucosa-associated Lymphoid Tissue (MALT): Lymphoid tissue located within the lining of major tracts (respiratory, digestive, urogenital). It constitutes about 50% of the lymphoid tissue in the human body.

AIDS

AIDS stands for Acquired Immuno Deficiency Syndrome. It is a deficiency of the immune system acquired during an individual's lifetime, not a congenital disease.

• Causative Agent: Human Immunodeficiency Virus (HIV), a member of a group of viruses called retroviruses. It has an RNA genome enclosed in an envelope.
• Transmission:
  • Sexual contact with an infected person.
  • Transfusion of contaminated blood and blood products.
  • Sharing infected needles (common in intravenous drug abusers).
  • From an infected mother to her child through the placenta.

• Mechanism of Infection:
  1. After entering the body, the virus enters macrophages.
  2. The viral RNA genome replicates to form viral DNA using the enzyme reverse transcriptase.
  3. This viral DNA incorporates into the host cell's DNA and directs the cell to produce new virus particles. The macrophage acts like an "HIV factory."
  4. Simultaneously, HIV enters and replicates within helper T-lymphocytes ($\mathrm{T}_{\mathrm{H}}$ cells).
  5. Progeny viruses are released, which attack other helper T-cells.
  6. This leads to a progressive decrease in the number of helper T-lymphocytes, severely weakening the immune system.
• Symptoms: There is a time lag (from months to 5-10 years) between infection and the appearance of symptoms. The person may suffer from fever, diarrhea, and weight loss. Due to a weak immune system, the person becomes vulnerable to opportunistic infections from bacteria (like Mycobacterium), viruses, fungi, and parasites (like Toxoplasma).
• Diagnosis: A widely used diagnostic test is ELISA (Enzyme-Linked Immuno-sorbent Assay).
• Treatment: Anti-retroviral drugs are only partially effective. They can prolong life but cannot prevent death.
• Prevention: Since there is no cure, prevention is the best option.
  • Organizations like NACO (National AIDS Control Organisation) and NGOs educate people about AIDS.
  • Ensuring safe blood transfusions.
  • Using only disposable needles and syringes.
  • Free distribution of condoms.
  • Advocating safe sex.
  • Promoting regular check-ups for susceptible populations.

Cancer

Cancer is one of the most dreaded diseases and a major cause of death globally. It is caused by the uncontrolled growth and division of cells.

• Normal Cells vs. Cancer Cells: Normal cells exhibit a property called contact inhibition, where contact with other cells inhibits their uncontrolled growth. Cancer cells appear to have lost this property.
• Tumors: Masses of cells resulting from uncontrolled division.
  • Benign Tumors: Remain confined to their original location and cause little damage.
  • Malignant Tumors: A mass of proliferating cells (neoplastic cells) that grow rapidly, invading and damaging surrounding tissues. They compete with normal cells for vital nutrients.
• Metastasis: This is the most feared property of malignant tumors. Cells from the tumor travel through the blood to distant sites and start new tumors there.

Causes of Cancer

Agents that cause cancer are called carcinogens.

• Physical Carcinogens: Ionising radiations like X-rays and gamma rays, and non-ionising radiations like UV rays, can damage DNA.
• Chemical Carcinogens: Chemicals in tobacco smoke are a major cause of lung cancer.
• Biological Carcinogens: Cancer-causing viruses called oncogenic viruses.
• Oncogenes: Normal cells have genes called cellular oncogenes (c-onc) or proto-oncogenes. When activated under certain conditions, these can lead to the cancerous transformation of cells.

Cancer Detection and Diagnosis

Early detection is crucial for successful treatment.

• Biopsy and Histopathological Studies: A piece of suspected tissue is sectioned, stained, and examined under a microscope.
• Blood and Bone Marrow Tests: Used for leukemias (blood cancer) to check for increased cell counts.
• Imaging Techniques:
  • Radiography (X-rays)
  • CT (Computed Tomography): Uses X-rays to generate a 3-D image.
  • MRI (Magnetic Resonance Imaging): Uses magnetic fields and non-ionising radiations to detect pathological changes in living tissue.
• Molecular Biology: Techniques can detect genes that predispose an individual to certain cancers.

Treatment of Cancer

• Surgery: Physical removal of the tumor.
• Radiation Therapy (Radiotherapy): Tumor cells are irradiated lethally, while taking care to protect surrounding normal tissues.
• Chemotherapy: Use of chemotherapeutic drugs to kill cancerous cells. These often have side effects like hair loss and anemia.
• Immunotherapy: Patients are given substances called biological response modifiers like α-interferon, which activate their immune system to help destroy the tumor.

Drugs and Alcohol Abuse

The use of drugs and alcohol is on the rise, especially among youth.

Commonly Abused Drugs

• Opioids:

  • Bind to opioid receptors in the central nervous system and gastrointestinal tract.
  • Heroin (smack): Chemically diacetylmorphine. It is obtained by acetylation of morphine, which is extracted from the latex of the poppy plant (Papaver somniferum).
  • Effect: A depressant that slows down body functions.

• Cannabinoids:

  • Interact with cannabinoid receptors in the brain.
  • Source: Obtained from the inflorescences of the Cannabis sativa plant.
  • Products: Marijuana, hashish, charas, and ganja.
  • Effect: Known for their effects on the cardiovascular system.

• Coca Alkaloids (Cocaine):

  • Source: Obtained from the coca plant Erythroxylum coca.
  • Effect: A potent stimulant of the central nervous system, producing euphoria and increased energy. It interferes with the transport of the neurotransmitter dopamine. Commonly called coke or crack. Excessive dosage causes hallucinations.

Other hallucinogenic plants include Atropa belladonna and Datura.

Adolescence and Drug/Alcohol Abuse

Adolescence (the period between 12-18 years) is a vulnerable phase for mental and psychological development.

• Causes for Abuse:
  • Curiosity, adventure, and experimentation.
  • Stress from academic pressure.
  • Perception that it is 'cool' or progressive, promoted by media.
  • Unstable family structures and peer pressure.

Addiction and Dependence

• Addiction: A psychological attachment to the effects of drugs and alcohol, such as euphoria. This drives people to take them even when they are self-destructive. With repeated use, the body's tolerance increases, leading to a need for higher doses.
• Dependence: The tendency of the body to show an unpleasant withdrawal syndrome if the regular dose is abruptly discontinued.
  • Withdrawal Symptoms: Anxiety, shakiness, nausea, and sweating. These can be severe and even life-threatening.

Effects of Drug/Alcohol Abuse

• Immediate Effects: Reckless behavior, vandalism, and violence.
• Overdose: Can lead to coma and death due to respiratory failure, heart failure, or cerebral hemorrhage.
• Warning Signs in Youth: Drop in academic performance, unexplained absence, lack of personal hygiene, isolation, depression, aggressive behavior, and changes in eating/sleeping habits.
• Long-term Effects:
  • Chronic use damages the nervous system and liver (cirrhosis).
  • Intravenous drug users are at high risk of acquiring serious infections like AIDS and Hepatitis B through shared needles.
  • Use during pregnancy can adversely affect the fetus.
• Misuse in Sports:
  • Athletes may misuse narcotic analgesics, anabolic steroids, and hormones to enhance performance.
  • Side-effects of Anabolic Steroids:
    • In Females: Masculinisation, aggressiveness, mood swings, abnormal menstrual cycles, excessive hair growth.
    • In Males: Acne, aggressiveness, depression, reduced testicle size, decreased sperm production, premature baldness.
    • In adolescents, it can lead to stunted growth.

Prevention and Control

"Prevention is better than cure."

1. Avoid Undue Peer Pressure: Respect a child's individual choice and personality.
2. Education and Counselling: Teach children to face problems and stresses. Channel their energy into healthy pursuits like sports, music, or yoga.
3. Seeking Help from Parents and Peers: Encourage seeking help immediately to vent feelings and get proper guidance.
4. Looking for Danger Signs: Alert parents and teachers should identify the warning signs.
5. Seeking Professional and Medical Help: Psychologists, psychiatrists, and de-addiction and rehabilitation programs can help individuals recover completely.