Human Health and Disease


According To WHO, health is defined as
“ Health is a state of complete physical, mental and social well-being and not merely an absence of disease or physical fitness.
Health is a state of body when all the organs and systems are functionally properly and a perfect balance is maintained b/w the environment and body.


Any conditions which interferes with the normal functioning of the body and impairs the body is called disease.

Types of diseases

On the basis of their period of their occurrence.

Congenital disease

These are inborn diseases which are present from birth and generally inherited.
Disease caused by gene mutation (colour blindness) and chromosomal mutation (Down Syndrome).

Acquired diseases

These occur only after birth and are non- inherited.
On the basis of their communication, acquired diseases are of 2 types:
  • Communicable/ infectious
  • Non- communicate/ Non- infections


These can be transmitted from an infected person to the healthy person by means of air, water, food and physical contact or vectors.
Depending upon the causative agent, communicable disease are of following types:
  • Bacterial Diseases: (Typhoid Pneumonia, Tuberculosis etc.)
  • Viral Diseases: (Dengue, Polio, influenza, AIDs, measles etc.)
  • Protozoan Diseases: (Malaria, amoebiasis, Kala azar, sleeping sickness etc).
  • Helminths Diseases: (Ascariasis, Elephantiasis, Prichinosis etc.)
  • Fungal Diseases: (Ringworm, athlete’s foot)
  • Rickettsial Diseases: (Typhus fever, Trench fever etc.)

On the basis of  their mode of transmission, communicable diseases are of two types:
Contagious diseases: (Direct contact)
These communicable diseases can spread from infected people to healthy people by actual contact b/w STDs, smallpox, chicken pox etc.

Non-contagious diseases: (Indirect contact)
These communicable diseases can spread from healthy people to infected people with food, air or water. Eg. Typhoid, Cholera or by microorganisms enters through host (eg. Malaria).

Non-communicable Diseases:

These do not spread from an infected person to a healthy person. These are of 4 types.
  • Deficiency disease-  Diabetes mellitus, Kwashiorkor (protein)
  • Degenerative disease- eg. Cardiovascular Arthritis
  • Cancerous diseases
  • Allergies- Asthma, Hay fever


These are such microorganisms like bacteria, viruses and fungi which could cause disease in humans.

Means of Spread:
Direct transmission: direct contact with an infected person (STDs), droplet infection (common cold), contact with soil (tetanus), animal bite (rabies) and transplacental transmission (syphilis).
Indirect transmission: Vector borne diseases (eg. Malaria), contaminated food and water (cholera), Air borne  (influenza), Formite borne, uncleaned hand (ascariasis).

Prevention of diseases ( Prophylaxis):
There are 3 limitations of the treatment approach of infectious diseases.
  • Body functions may never recover completely.
  • Patient is bed- ridden for some time depending on the severity of disease.
  • Infected people act as the source of spread of disease to even healthy person.
So, it is right to say that "Prevention is better than cure".

There are 2 ways of Prophylactic measures:
General prophylactic measure:
  • Avoid overcrowding and providing hygienic living conditions.
  • Providing safe drinking water.
  • Proper sanitation of human foetus.

Specific prophylactic measures:
Vaccination and immunization.
Principle of Treatment:
There are two ways of treatment of infections diseases:
Symptom directed treatment is directed to reduce the effect of diseases which are due to inflammation of certain body tissues.
Pathogen directed treatment is directed to kill the microbes using certain chemical contibioties.

Some Important Protozoan Diseases

Amoebiasis: (Amoeboid dysentery)
Causative agent: Entamoeba histolytica (protozoa)
Epidemiology: Direct and oral and sometimes by vectors (house- flies).
Symptoms: Ulceration, acute diarrhoea, abdominal pain, stools with excess mucus and blood clot.
Prevention/control: Antibiotics like paramycin, erythromycin. Aureomycin and most effective metronidazole.
Site of effect: Pathogen secretes cytolysin enzymes which damage intestinal mucosa.
Causative agent: Plasmodium- P. vivax, P. malariae, P-falciparum (malignant malaria).
Epidemiology: Oral contact and by vector like female anopheles mosquito.
Symptoms: Fever, weakness, headache
Prevention/control: Durg quinine (extracted from bark of Cinchona plant).

Life Cycle of Plasmodium

It is Digenetic (2 hosts):
  • Man (secondary)
  • Anopheles (primary)

Life cycle of plasmodium is Triphasic.
  • Schizogony
  • Gamogony
  • Sporogony

  • It is the asexual phase of multiplication of parasites in the man.
  • The sporozoites enter into the blood of man along with the drop of saliva, when a female anopheles bites him.
  • Schizogony is divided into 2 phases:
    1. Hepatic
    2. Erythrocytic
  • The sporozoites enter the liver cells, become rounded and feed on the cytoplasm and multiply to form large numbers of  crypto merozoites.
  • Some of the crypto merozoites enter into the fresh liver cells and repeat the process.

  • The crypto merozoites enter the erythrocytes and feed on their haemoglobin, grow and undergo multiple fission to form merozoites. The haeme of the haemoglobin is converted into a toxic substance called haemozoin which is responsible for material attack.

  • It is the phase of sexual reproduction.
  • In it merozoites enter into fresh RBC and form two types of gametocytes, micro and macro.
  • These gametocytes are sucked by female anopheles.
  • In the stomach of anopheles, gametocytes form 2 types of gametes – sperm and ova.
  • Fertilization occurs in the stomach of the mosquito and zygote is formed.
  • As sexual reproduction occurs in mosquito  it is the primary host, while man acts as secondary host.

  • It is the phase of asexual reproduction.
  • zygote changes into oocyst in the wall of stomach, feeds and undergoes multiple fissions to form large no. of sporozoites.
  • Oocyst ruptures and sporozoites are released.
  • Most of the sporozoites enter the salivary gland and wait to be injected into another man.

Some Important Helminth Diseases

  • Caused by: Helminthes; Ascaris lumbricoides
  • Symptoms: internal bleeding, blockage of intestinal passage, anaemia, muscular pain.
  • Epidemiology: contaminated vegetables, fruits, soil etc.
  • Control (prophylaxis): Mixture of oil of chenopodium and tetrachloroethylene.

Filariasis (Elephantiasis)
  • Caused by: Wuchereria bancrofti and Wuchereria malayi
  • Symptoms: Normally caused inflammation of organs, affects the lymph vessels of lower limbs, genital organs are also affected resulting in gross deformities.
  • Epidemiology: female culex mosquito is the vector.
  • Control: Anti-helminth drugs like Hetrazin and Diethylcarbamazine.

Fungal disease

  • Caused by: fungi belonging to the genera Microsporum, Trichophyton and  Epidermophyton.
  • Epidemiology: from soil or fomite borne or direct contact.
  • Symptoms: dry and scaly lesions on skin, nails, scalp and itching.
  • Control: Antibiotics


  • Immunity or disease resistance is the ability of an organism to resist the development of a disease.
  • The study of immunity is called immunology; while the infected person with no disease is known as immune.
  • Immune system forms the third line of defense.
  • Any foreign substance which when enters the body, is capable of stimulating an immune response is called an antigen.
  • The protective chemicals produced by the body in response to antigens are known as antibodies.
  • Antibodies are a class of bodies called immunoglobulins.
  • Immunity is of two types:
    (a)Innate immunity
    (b) Acquired immunity

Innate Immunity

  • It is a non-specific type of defense that is present at the time of birth.
  • This is accomplished by providing different types of barriers to the entry of the foreign antigens into our body.
  • It consists of following barriers:

Physical barriers:
They include skin and mucus coated epithelium of the respiratory tract, gastro- intestinal and urino-genital tract where the mucus helps in trapping microbes entering our body.

Physiological barrier: They include
  1. Acidity of stomach
  2. Lysozyme in saliva
  3. Tear from eyes
All prevent microbial growth.

Cellular barrier:
They include the following specialized cells, which phagocytose and destroy the microbes.
  1. Natural killer lymphocytes (NTC cells)
  2. Neutrophils
  3. Monocytes
  4. Macrophages

Cytokine barrier:
Interferons produced by viral infected cells protect the non- infected cells from viral infections.

Acquired immunity (Adaptive Immunity)

  • Acquired immunity refers to the immunity, a person acquires after birth; either by contacting the disease or by vaccination.
  • It is pathogen specific and is present only in vertebrates. It has the following characters:
It has the ability to distinguish many different foreign molecules.
When the immune system encounters a pathogen for the first time, it develops an immune response by which a pathogen is eliminated (primary response). It also retains some memory cells which evoke a heightened immune response in further encounters (secondary response).

Acquired immunity has 2 limbs
  1. Humoral/ Antibody mediated immunity
  2. Cell mediated immunity.

Humoral immunity
  • It consists of the antibodies that are circulating in the body fluid (humor/plasma).
  • The antibodies produced by B- lymphocytes in response to the antigens are collectively called immunoglobulins and are of various types i.e. IgA, IgD, IgE, IgM,  IgG.
  • Each antibody consists of four polypeptide chains. Two of the polypeptide chains are called heavy chains (H) while the other two are short and are called light chains (L), hence an antibody is represented as H2 L2.

Cell- mediated immunity:
  • It is mediated by T- lymphocytes. These are 2 groups of  T- lymphocytes:
  • Cyto - toxic/ killer- T-cells which kill the specific target cell by a variety of mechanisms.
  • Helper T-cells which activate the specific B-cells to produce antibodies.
  • T-lymphocytes   are responsible for graft rejection.

Acquired immunity can also be classified into two types:
  • Active
  • Passive

Vaccination and Immunisation
  • The principle of vaccination and immunisation is based on the property called memory of the immune system.
  • The vaccines generate antibodies that neutralize the toxin/pathogen and also produce memory B-cell and T-cell which recognize the pathogen in subsequent encounters and produce antibodies. This type of immunization is called active immunization.
  • If a quick immune is needed as in tetanus infection, preformed antibodies or antitoxin injected into the patient. This type of immunization is called passive immunisation .
  • Recombinant DNA technology has allowed the production of antigenic polypeptides of pathogens in other microbes like yeast and bacteria. Eg. Hepatitis-B vaccine is produced using yeast cells.


Allergy can be defined as the hyper- sensitive reaction of the immune system of a person to some foreign substances called allergen which either comes in contact with or enters the body.
  • The antibodies produced in response to allergens are IgE type.
  • The common symptoms of allergy:
    • Rashes
    • Sneezing
    • Watery eyes
    • Running nose
    • Difficulty in breathing.
These symptoms are produced due to release of histamine and serotonin from the mast cells.
Drugs like anti- histamine, adrenaline and steroids quickly reduce the symptoms of allergy.

Auto- Immunity:

The auto- immune disorders are those disorders caused by the bodies of the immune system when it goes off the track and starts destroying “self- cells and molecules”.
Eg. Hashimoto’s thyroiditis, insulin-dependent diabetes, Rheumatoid arthritis etc.

Immune System

The main function of the immune system is to recognize the foreign molecules, respond to them and keep a memory of them.
It also play a role in
  • Organ transplantation
  • Allergic reactions
  • Auto- immune diseases
Immune system consists of following:
  • Lymphoid organs
  • Bone Marrow
  • Thymus
  • Spleen
  • Lymph nodes
  • Mucosa associated lymphoid tissue (MALT)
These are the organs where origin, maturation and proliferation of lymphocytes takes place.
Primary Lymphoid organs:
Primary lymphoid organs are those where the immune lymphocytes undergo maturation/ differentiation into antigen- specific lymphocytes.
Example: Bone Marrow and Thymus.
Secondary Lymphoid organ:
Secondary lymphoid organs are those where the lymphocytes interact with the antigen and proliferate to form clone effector cells and memory cells.
Example: Spleen, lymph nodes, tonsils, appendix and peyer's patches of the small intestine.
Bone Marrow:  
  • It is the main lymphoid organ where all types of blood cells including lymphocytes are formed.
  • Bone Marrow provides the micro- environment for the development and maturation of B- lymphocytes.
  • It is located beneath the chest bone near the heart.
  • This grand keeps reducing in size with age.
  • It provides the micro- environment for the development and maturation of T- lymphocytes.
  • It mainly contains lymphocytes and phagocytes.
  • It acts as a filter of blood.
  • It is also a reservoir of erythrocytes.
Lymph nodes:
  • They are small solid structures found at different points along the lymphatic system.
  • They act as a filter and trap the microbes that have entered the lymph.
  • Antigen trapped in them activate the lymphocytes present in the lymph nodes and produce immune response.
  • Lymphoid tissues located within the mucosal lining of major tracts. (respiratory/ digestive/ urino- genital tract) is called MALT.
  • It accounts for about 50% of lymphoid tissue in the human body.

AIDS (Acquired Immunodeficiency Syndrome)

  • It was first reported in 1981.
  • It is caused by human Immunodeficiency Virus. (HIV) which is a retrovirus (single stranded RNA)

Transmission of HIV occurs in one of the following ways:
  • By sexual contact with an infected person.
  • Transfusion of contaminated needles.
  • From infected mother to child through placenta.
The following individual are at high risk of giving disease:
  1. Those who have multiple sexual partners.
  2. Drug addicts taking drugs intravenously.
  3. Individual who requires repeated blood transfusion.
  4. Children born to an infected mother.

Life cycle of HIV/Mechanism:
  • The virus after getting into the body of a person enters the macrophages.
  • The RNA replicates and DNA is formed by reverse transcriptase. (reverse transcription)
  • The viral DNA gets incorporated into the host cell DNA to form prophage and replicates along with host DNA and direct the infected cell to produce virus particles.
  • The macrophages continue to produce virus particles.
  • Finally the infected host cell is lysed and many HIV viruses are released which infect helper- T cells, replicates and form progeny virus.
  • So, the process is repeated which caused a progressive decrease in the number of helper T- cells.
  • Now the person becomes easily infected by bacteria like mycobacterium, viruses and even parasites like Toxoplasma.
  • The person is unable to protect himself/ herself against any infection.

AIDs can be diagnosed by ELISA (Enzyme Linked Immunosorbent Assay) and Western blot test.

  • National AIDs  control organizations (NACO) and NGOs are trying their best to educate people about AIDs.
  • WHO has started a number of programs to prevent spreading of HIV infection. Some such steps include
  1. Ensuring use of disposable needles and syringes.
  2. Checking blood for HIV.
  3. Controlling Drug Abuse.
  4. Promoting regular checkup for HIV in susceptible populations.
  5. Avoiding prostitution, multi- partner sex and homosexuality etc.
Till today, there is no specific therapy against HIV infection although Azidothymidine (AZI) has been found to suppress AIDS virus.
Treatment with antiviral drugs is only partially effective. they can only prolong the life of the patients and can't prevent death.


Cancer is characterized by uncontrolled growth and division of certain body tissues, so forming a tumor.
Transformation of normal cells into cancerous cells is induced by carcinogen.
Carcinogens are those physical, chemical and biological agents which bring about uncontrolled proliferation of cells ie. Cancer.
These are of following types:
(1)Physical carcinogen
Eg. UV rays, X- rays,  Y- rays
(2)Chemical carcinogen
Eg. Aniline dyes, chemicals present in tobacco smoke.
(3)Tumor viruses (oncogenic viruses)
Note: Study of cancer - oncology
Causative genes -oncogenes
The cancer cells differ from the normal cells in the following ways:
  1. There is a breakdown of regulatory mechanisms which control normal cell growth, division and differentiation.
  2. Cancer cells do not show contact inhibition and show uncontrolled growth.
  3. Cancer cells show metastasis. ie. They detach from the tumor and move to distant sites through body fluid and develop secondary tumor.
Types of tumor:
Benign Tumor:
They remain confined to their original location and do not spread to other parts, they cause little damage.
Malignant Tumor:
  • They are masses of neoplastic/ proliferating cells, which grow rapidly, invade and damage the surrounding normal tissue/ cells.
  • These cells complete with the normal cells for vital nutrients and disrupt normal metabolism.
  • These cells show the property of metastasis.
Diagnosis of Cancer:
Cancer can be detected by:
  • Biopsy and Histopathological studies of tissue.
  • Blood and Bone Marrow test for increased cell count as in leukemia (blood Cancer)
  • Use of techniques like radiography, Magnetic resonance imaging (MRI) and computed Tomography (CT) for cancer of internal organs.
  • Use of antibodies against Cancer- specific antigens.
  • Applying  principle of molecular biology to detect genes in individuals with inherited susceptibility to certain cancer.
Treatment of Cancer:
The following  one or more methods in combination can help to treat cancer:
The tumor cells are surgically removed to reduce the load of cancerous cells.

The tumor cells are irradiated wholly but taking care of normal surrounding cells.

Certain drugs are used to kill the cancerous cells, but the majority of drugs have side-effects such as hair-loss, anemia etc.

This involves the use of biological response modifiers like alpha-interferons as monoclonal antibodies which activates the immune system and helps in destroying tumors.


Drug Abuse

The drugs that are commonly abused include opioids, cannabinoids, cola-alkaloids, barbiturates, amphetamines, benzodiazepines and Lysergic acid diethylamide ( LSD).
Kinds of drugs:
  • These act as depressants and analgesics so are commonly called pain-killers.
  • These bind to their specific opioid receptor present in the CNS and gastro-intestinal tract.
  • eg. Morphine and heroin (derivatives of opium).
  •  It is obtained from the latex of poppy plant (Papaver somniferum).
  • It is used to reduce pain after surgery.
Heroin (smak ): Also called brown sugar
  • It is chemically called Diacetylmorphine. It is a bitter, white, odourless, crystalline compound obtained by acetylation of morphine.
  • It is generally taken by smoking and injection.
  • It is depressant and slows down the body functions.
2. Cannabinoids:
  • These dilate the pupil, increasing urination and high sugar level.
  • These interact with cannabinoid receptors present in the brain.
  • natural cannabinoids are obtained from inflorescence of Cannabis sativa.
  • There are 2 species of hemp plants where dried leaves and flower yield drugs.
  1. Cannabis indica provide bhang, ganja and charas.
  2. Cannabis sativa provide marijvana.
  • The active components of cannabinoids is Delta-9- tetrahydrocannabinol (THC)
  • Cannabinoids are taken by inhalation and oral- ingestion, they affect the cardiovascular system of the body.
  • They are abused by sports persons in recent times.
3. Coca- alkaloids/ cocaine:
  • It is obtained from the leaves and young branches of the plant Erythroxylum coca (coca plant).
  • Cocaine interferes with the transport of neurotransmitter dopamine.
  • It is usually taken by smoking.
  • It has a potential stimulating action on the CNS and produces a sense of Euphoria and increase energy but excessive use causes severe headache, convulsion, hallucinations and death due to cardiovascular or respiratory fail-ure.
4. Caffeine
Obtained from the seed of the coffee plant, Coffea arabica, leaves of tea- plant (Camellia sinensis) and seeds of cocoa plant.
It is used as cardiac and nervous stimulants.

5. Amphetamines
These are synthetic drugs and act as a strong stimulant of CNS.
6. Hallucinogen: (Psychedelic drugs)
These are those drugs which change thoughts, feelings and perceptions of an individual who claims that he can “see sounds” and “hear colour”.
These cause hallucinations, nightmares, floating sensation, increased sugar level in blood and increased urination.
Products from plants like Atropa belladonna and Datura spp are hallucinogenic.
Lysergic Acid Diethylamide (LSD) is the most dangerous hallucinogen causing chromosomal and foetal abnormalities. It is obtained from the fungus.
7. Sedative Drugs:
These acts as depressant and suppress the activities of CNS.
Eg. Benzodiazaphines, Barbiturates (sleeping pills) are some examples.

  • Tobacco is usually chewed or smoked or used as snuff.
  • It contains mainly nicotine which is stimulant and toxic.
  • It is derived from the dried and cured leaves of young branches of Nicotiana tabacum and N. rustica. (family Solanaceae).
  • Nicotine stimulates the adrenal glands to release adrenaline and noradrenaline which increase the blood pressure and heart beat.
  • Smoking of tobacco increases the chances of lung cancer, bronchitis, emphysema (inflammation of alveoli), coronary heart disease, cancer of throat, gastric ulcer etc.
  • Smoking of tobacco also increases the CO content of blood and reduces Concentration of haemoglobin bound oxygen, thus causing deficiency of oxygen in the body.
  • Chewing of tobacco causes oral cancer.
  • World No tobacco day:  31st May (2002)


Alcohol is a depressant and it affects the CNS.
Regular consumption of alcohol either in low Concentration/ high Concentation causes dependency on alcohol which is called alcoholism.

Addition and dependence:

The physical and mental dependence on smoking, alcohol and drugs is called addiction. The person who has become dependent upon this addiction is called an addict.
Following  are the causes of drug/ alcohol abuse:
  1. Curiosity
  2. Needs for adventure
  3. Excitement
  4. Experimentation
  5. To escape from stress
  6. Unsupportive family structure.
With repeated use of drug/ alcohol the tolerance level of the receptor in our body increases and now they respond only to higher use of drug or alcohol.
If the regular dose of alcohol/ drug is abruptly discontinued, the body manifests characteristics and unpleasant withdrawal symptoms which can be anxiety, nausea, sweating etc.
World Anti- Drug day—26th June
Effects of Drugs/ Alcohol abuse
  • Reckless behavior, vandalism and violence.
  • Excess dose can lead to coma and death.
  • Fluctuation in weight
  • Aggressive and rebellious behaviour
  • Change in sleeping and eating habits.
  • If drugs are taken intravenously it can lead to infections like AIDS and hepatitis.
  • Damage CNS and livers.

Prevention and Control
  • Avoid undue peer pressure
  • Education and counselling to face problems and stresses and to accept failures and disappointments as a part of life.
  • Seeking help from parents and peers could help to Vent their feeling of anxiety and guilt.
  • Addicts can be rehabilitated by seeking professional and medical help from the highly qualified psychologist and psychiatrist.

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