Human Health and Disease

Human Health and Disease for UPSC aspirants

Human health is the state of complete physical, mental, and social well-being. Health increases productivity and ensures longevity.

What is Human Health?

  • Human health is the state of complete physical, mental, and social well-being.
  • Health increases productivity and ensures longevity.

Ways to Ensure Good Health

  • Balanced diet
  • Personal hygiene
  • Exercise
  • Awareness of prevention and control of diseases
  • Proper waste disposal and control of vectors
  • Vaccination

Why do Diseases Occur?

  • Genetic reasons − Innate deficiencies and inheritable defects
  • Infections
  • Sedentary lifestyle − Junk food, consumption of alcohol/drugs, lack of exercise

Common Diseases in Humans

Pathogenic Diseases

  • Pathogens are parasites that enter the human body through various means, multiply, and interfere with normal vital activities.

Bacterial Diseases

  • Typhoid
    • Pathogen − Salmonella typhi
    • Spreads through − Contaminated food and water
    • Site of infection − Small intestine
    • Symptoms − High fever, stomach pain, headache, loss of appetite, constipation, and intestinal perforations in severe cases
    • Confirmatory test − Widal test
  • Pneumonia
    • Pathogens − Streptococcus pneumoniae and Haemophilus influenzae
    • Spreads through − Droplets/aerosols released from infected person, sharing of glasses or utensils
    • Site of infection − Alveoli (gets filled with fluid, difficulty in breathing)
    • Symptoms − Fever, chills, cough, headache, lips and nails become grey in severe cases

Viral Diseases

  • Common cold
    • Pathogen − Rhinoviruses
    • Site of infection − Nose and respiratory passage
    • Spreads through − Droplets released from coughing or sneezing, or contaminated objects
    • Symptoms − Nasal congestion and discharge, sore throat, cough, headache, tiredness

Protozoan Diseases

  • Malaria
    • Pathogen − Plasmodium species. ( P. vivax, P. falciparum, P. malaria )
    • Vector − Female Anopheles mosquito
    • Symptoms − High-grade fever, chills
  • Amoebiasis
    • Pathogen − Entamoeba histolytica
    • Vector − Housefly
    • Site of infection − Large intestine
    • Symptoms − Constipation, abdominal pain, cramps, stools with mucous, and blood clots

Fungal Diseases

  • Ringworms
    • Pathogens − Genera MicrosporumTrichophyton, and Epidermophyton
    • Spreads through − Towels, clothes, comb (Fungus is acquired from soil)
    • Symptoms − Appearance of dry, scaly lesions on various body parts with intense itching

Diseases Caused by Worms

  • Ascariasis
    • Pathogen − Roundworm, Ascaris
    • Spreads through − Water, vegetables, and fruits contaminated by the faeces of an infected person
    • Symptoms − Internal bleeding, muscular pain, fever, anaemia, blockage of intestinal passage
  • Elephantiasis (filariasis)
    • Pathogen − Wuchereria W.malayi and W.bancrofti )
    • Spreads through − Bite of female mosquito vector
    • Symptom − Chronic inflammation of the organs, usually the lymphatic vessels of the lower limb

Life Cycle of Plasmodium

  • Plasmodium requires two hosts to complete its life cycle.
  • When a female Anopheles mosquito bites a healthy human, it releases Plasmodium, which lives in its body as sporozoite (infectious form).
  • The parasites multiply (asexual reproduction) in the liver cells and finally burst the liver cells. Sporozoites are released in blood.
  • Parasites enter RBCs and further multiply (asexual reproduction) here and finally burst RBCs.
  • The bursting of RBCs is accompanied by the release of a toxic substance called haemozoin (associated with fever and chills).
  • In the RBCs, only sporozoites change into gametocytes (sexual stage). Gametocytes multiply.
  • When the diseased person is bitten by a female Anopheles mosquito, gametocytes are introduced into the mosquito.
  • Gametocytes fertilise and develop inside the intestine of mosquitoes to form sporozoites.
  • Sporozoites are stored in the salivary glands of mosquitoes and are released into the healthy person who is bitten by this mosquito.


What is immunity?

  • The ability of the body to fight the disease-causing organisms is called immunity.

Types of immunity

  • Immunity is of two types − innate immunity and acquired immunity.
  • Innate immunity − It is present from the time of birth. It is nonspecific. It consists of 4 kinds of barriers.
    • Physical barriers − Skin and mucus coating of the respiratory, gastrointestinal, and urogenital tract prevent the entry of microbes into the body.
    • Physiological barriers − Acid in the stomach, saliva in the mouth, tears from eyes
    • Cellular barriers − Blood has leukocytes such as polymorph nuclear leukocytes, monocytes, etc. and tissue has macrophages which phagocytose the microbes.
    • Cytokine barriers − Special proteins called interferons are secreted by virus-infected cells that prevent the further spread of viral infection.
  • Acquired immunity − It is acquired, which means that it is produced in response to an encounter with a pathogen based on memory. It is pathogen-specific.
    • When a pathogen for the first time infects a person, low-intensity immune response is generated (primary response).
    • When the same pathogen attacks again, an intensified immune response in generated, thereby preventing the occurrence of disease (secondary response).
    • Acquired immunity involves two types of cells − B-lymphocytes and T-lymphocytes.
    • B-lymphocytes: Secrete proteins called antibodies in response to pathogens Antibodies are specialized proteins with 4 peptide chains (2 light and 2 heavy), hence denoted as H 2 L 2 . IgA IgM, IgE, etc. are examples of some of the antibodies. They generate a humoral immune response (found in blood).
    • T-lymphocytes: They help B-cells to produce antibodies. They generate cell-mediated immune responses. This response helps the body differentiate between ‘self’ and ‘nonself’ as occurs in graft rejection.

Difference between active immunity and passive immunity

  • Active Immunity
    • This is the naturally acquired immunity produced in the host body in response to an antigen.
    • Immunization and the body naturally getting immune to a microbe that had caused infection previously are examples of active immunity.
  • Passive immunity
    • When readymade antibodies are provided to an individual to protect against foreign agents
    • Colostrums present in the mother’s milk contain IgA. Also, the foetus gets antibodies from the mother through the placenta.

How does vaccination help?

  • Vaccines are nothing but inactivated pathogens.
  • These inactivated pathogens when introduced into the body produce a primary immune response and antibodies are produced against the pathogen.
  • Memory B and T-cells are produced.
  • Now when the pathogen again attacks the person, memory B and T-cells generate a massive immune response and the pathogen is killed.

Problems of the immune system

  • Allergies
    • Exaggerated immune response to certain antigens present in the environment
    • Allergens − Substances in response to which allergy is produced E.g., dust, pollen, etc.
    • Antibodies involved − IgE type
    • During allergic reactions, chemicals such as histamines and serotonins are released.
    • Symptoms − Sneezing, watery eyes, difficulty in breathing, etc.
    • Allergy test − The patient is injected with small doses of allergens to monitor his response.
    • Antihistamines, adrenalins, and steroids may be given so that the symptoms of allergy subside.
  • Autoimmunity
    • In autoimmunity, the body generates an immune response against its own cells.
    • Reasons − Genetic and other unknown reasons
    • Example − Rheumatoid arthritis is an autoimmune disease.

Human immune system

  • Lymphoid organs are of two types − primary lymphoid organs and secondary lymphoid organs.
  • Primary lymphoid organs consist of bone marrow and thymus. Here, immature lymphocytes are differentiated to form antigensensitive lymphocytes.
    • Bone marrow − Here, all blood cells including lymphocytes are produced.
    • Thymus − It is responsible for the maturation of T-lymphocytes. This lobed organ is situated near the heart and keeps on reducing in size as age increases.
  • Secondary lymphoid organs − Lymphocytes migrate here after attaining maturity. It includes spleen, lymph nodes tonsils, Peyer’s patches, and appendix.
    • Spleen − Large bean-shaped organ containing lymphocytes and phagocytes, which acts as a filter for blood
    • Lymph nodes − Located at different points throughout the immune system, they trap the antigens present in lymph or tissue fluid, and these antigens cause activation of lymphocytes and generation of immune response.
  • MALT (Mucosal associated lymphoid tissue) − Lines major tracts (respiratory, digestive, urogenital, etc.); constitutes 50% of lymphoid tissue in the body

AIDS & Cancer

AIDS (Acquired Immuno Deficiency Syndrome)

  • Caused by HIV (Human Immunodeficiency Virus) [HIV is a retrovirus (RNA virus)]
  • Transmission of HIV occurs through:
    • Sexual contact with an infected person
    • Sharing infected needles (as in the case of intravenous drug abusers)
    • Transfusion of contaminated blood
    • Infected mother to child through placenta
  • The time lag between infection and appearance of symptoms – A few months to many years (510 years)
  • How does AIDS infection spread?
    • The virus enters the body of a person and enters macrophages.
    • Here, the virus replicates (viral RNA reverse transcribes to viral DNA, which gets incorporated into the host’s DNA and subsequently new viral particles are produced).
    • Macrophages become a virtual HIV factory.
    • Thereafter, HIV enters helper T-lymphocytes, replicates, and produces progenies.
    • As the progenies are released, they attack other T-lymphocytes.
    • Therefore, T-lymphocytes start decreasing in number and the immune response of the person becomes weak.
    • Even infections which could be overcome easily start aggravating.
  • Diagnosis of AIDS − By ELISA (Enzyme-Linked Immuno Sorbent Assay)
  • Treatment − No permanent cure; antiretroviral therapies can prolong the life of the patient.
  • Prevention of AIDS
    • Ensuring the use of disposable syringes
    • Screening blood from blood banks
    • Advocating safe sex
    • NACO (National AIDS Control Organization) and many NGOs are doing a lot to create awareness among people.


  • The process of development of cancer is called oncogenic transformation.
  • Normal cells have the property of contact inhibition (stoppage of growth on coming in contact with other cells), but cancer cells lose this property.
  • As a result, cancer cells divide continuously to give rise to a mass of cells (tumours).
  • Tumours are of 2 types − benign and malignant.
  • Benign tumours − remain confined to their original location and do not spread.
  • Malignant tumours− These exhibit metastasis i.e., the cells sloughed from such tumours reach distant sites and wherever they reach, new tumour is formed.
  • Malignant tumours actually represent cancer. The cells actively divide, grow, and starve the normal cells of vital nutrients.
  • Causes of cancer
    • Carcinogens − Physical, chemical, and biological agents that cause cancer. For Example, ionizing radiation (Xrays and gamma rays), nonionizing radiation (UV)
    • Oncogenic (cancer-causing) viruses − They have viral oncogenes (cancer-causing genes).
    • Sometimes normal genes in our body called protooncogenes get converted into cellular oncogenes that cause cancer.
  • Diagnosing cancer
    • Biopsy and histopathological studies
    • Biopsy − Suspected tissue is cut into thin sections and examined microscopically
    • Radiography, CT scan (computed tomography), and MRI (Magnetic resonance imaging) are techniques for diagnosing cancers.
    • CT Scan − 3D imaging of internals of an organ is generated by Xrays.
    • MRI Scan − Pathological and physiological changes in a living tissue are detected by using magnetic fields and nonionizing radiations.
    • Immunological and molecular biological diagnostic techniques can all be used to detect cancers.
    • Identifying certain genes, which make an individual susceptible to cancers, can help to prevent cancers.
  • Treatment of cancer
    • Radiotherapy − Tumour cells are irradiated to death. Also, proper care is taken for protecting surrounding normal tissues.
    • Chemotherapy − Drugs specific for particular tumours are used to kill cancer cells. They have side effects such as hair loss, anaemia, etc.
    • Immunotherapy − Biological response modifiers such as αinterferons are used. They activate the immune system of patient and helps in destroying the tumour.

Commonly Abused Drugs

Opioids (Heroin)

  • Source: Acetylation of morphine extracted from the latex of poppy plants ( Papaver somniferum )
  • Consumed by: Snorting or injection
  • Properties: White, bitter and odourless
  • Mode of action: Binds to opioid receptors present in the CNS and GI tract
  • Effect: It is a depressant; slows down body functions


  • Source: Inflorescences of the plant Cannabis sativa
  • Consumed by: Inhalation or oral ingestion
  • Mode of action: Binds to cannabinoid receptors present in the brain
  • Effect: Affects the cardiovascular system


  • Source: Coca plant Erythroxylum coca , found in South America
  • Consumed by: Snorting
  • Mode of action: Interference with the transfer of neurotransmitter, dopamine
  • Effect: Stimulates the CNS, producing a sense of euphoria and increased energy; excessive dosages cause hallucination

Drugs Normally Used as Medicines

  • Drugs like barbiturates, amphetamines, benzodiazepines, LSD (Lysergic acid diethyl amides) are used as medicines to help patients with mental illness and insomnia.
  • Morphine: It is a pain killer which is used for patients who have undergone surgery, but it is also abused.


  • Present in tobacco, which is smoked, chewed or snuffed.
  • Mode of action: Stimulates the adrenal gland to release adrenaline and noradrenaline.
  • Effect: Increases blood pressure and heart rate

Ill Effects of Smoking

  • Increased risk of diseases like bronchitis, emphysema, coronary heart disease, gastric ulcer and cancer (throat, lung and urinary bladder)
  • Increased carbon monoxide levels in the blood, leading to oxygen

Alcohol / Drug Abuse

Causes of alcohol/ Drug Abuse

  • Alcohol / drug abuse normally starts in adolescence (period between 12-18 yrs − transition phase between childhood and adulthood).
  • Many adolescents are motivated towards drugs/ alcohol due to curiosity and experimentation.
  • Peer pressure, academic stress, unstable family structure further incline youth towards alcohol/ drug abuse.
  • Perception of consuming alcohol / drug being cool and progressive and use of alcohol/drug in television, movies, etc. further promote this habit.

Alcohol/ Drug Addiction

  • When a person uses alcohol/ drug repeatedly, he becomes addicted.
  • Addiction refers to psychological attachment to certain effects such as euphoria and temporary feeling of wellbeing associated with use of alcohol or drugs.
  • In addiction, tolerance level of receptors present in our body increases towards the drug.
  • This drives the person to use them even when they are not required or when they tend to harm his health / family life.
  • Subsequently, the user runs into a vicious circle of addiction and subsequent dependence.
  • Dependence leads to manifestation of withdrawal syndrome on discontinuation of use.
  • Withdrawal syndrome − Anxiety, nausea, sweating, shakiness, and sometimes may be lethal

Effects of Alcohol/ Drug Abuse

  • Immediate effect − Vandalism, violence, and reckless behaviour
  • Drop in academic performance, lack of interest in personal hygiene, rebellious behaviour, and change in eating and sleeping patterns, weight and appetite fluctuations
  • Mental, psychological, and financial loss not only to the user, but also to his family.
  • Those who take drugs intravenously have a high risk of acquiring deadly diseases such as AIDS and hepatitis B.
  • Damage to the nervous system and liver (cirrhosis)
  • Use of anabolic steroids by sportsperson has adverse effects:
    • In females − Increase of masculinity, aggressiveness, depression, abnormal menstrual cycle, facial hair growth, enlargement of clitoris, and deepening of voice
    • In males − Acne, aggressiveness, depression, reduction in size of testicles, decreased sperm production, enlargement of the prostate gland, breast enlargement, premature baldness
  • Ultimately, prolonged use of alcohol/drugs leads to coma and death.

Preventing Alcohol/ Drug Abuse

  • It is better to prevent the inclination of an individual towards alcohol/ drugs right from adolescence. Some of the ways of prevention are:
    • Avoid peer pressure − Understand the unique personality and capabilities of a child
    • Education and counselling − A child must be taught to accept success and failure equally. Especially during adolescence, he must be inclined towards constructive activities such as music, yoga, sports, and reading based on his interests.
    • Help from parents and peers − This includes proper guidance, advice, and trust to overcome problems such as stress and guilt.
    • Identifying danger signals − If any sign or symptom of alcohol / drug abuse is seen in the adolescent by family or friends, then it should not be ignored because prevention is better than cure.
  • Seeking medical help − Psychologists and rehabilitation programs surely help an addict. Medical help should be sought to prevent further damage.

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