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Health is a state of complete physical, mental and social well-being.

Health- Health is a state of complete physical, mental and social well-being.

Health increases the longevity of people and reduces Infant and maternal mortality rate.

Good health can be achieved by balanced diet, personal hygiene, regular exercise, yoga, vaccination against infectious diseases, proper disposal of wastes, control of vectors and maintenance of hygienic food and water resources.


Factors affecting on health

  1. Genetic disorders- deficiencies with which a child is born and deficiencies/defects which the child inherits from parents from birth.

  2. Infection- the body is being exposed to disease causing agents such as bacteria, viruses etc...,

  3. Lifestyle- including food and water we take, rest and exercise we give to our bodies, habits that we have or lack etc...,

  4. State of the mind- it affects the neural and endocrine system which in turn affects our immune system. Immune System performs a vital role in keeping the body in a healthy state.



Disease is a condition in which functioning of one or more organs or systems of the body is adversely affected,

characterized by various signs and symptoms.


Diseases can be broadly grouped into infectious and noninfectious diseases.

Infectious diseases are the disorders which are easily transmitted from one infected person to other, that are caused by pathogenic organisms such as bacteria, viruses, parasites or fungi.

Non-infectious diseases are the disorders that are not transmitted from one person to another

Common infectious diseases in human:

Infectious diseases are classified on the basis of pathogen.

Disease causing organisms are called pathogens. Examples: bacteria, viruses, fungi, protozoans, helminths etc...,

  1. Bacterial diseases- Typhoid, pneumonia, diphtheria, bacterial dysentery, plague…

  2. Viral diseases- Common cold, polio…

  3. Protozoan diseases- Malaria, amoebiasis…

  4. Fungal diseases- Ringworm…

  5. Helminthic diseases- Ascariasis, filariasis, taeniasis…


Bacterial diseases:


  • It is caused by pathogenic bacteria Salmonella typhi.

  • It is spread by contaminated food and water.

  • It generally enters the small intestine and then migrates to other organs through Blood.



  1. Sustained high fever (39 oCto 40 oC),   

  2. Weakness             

  3. Stomach pain

  4. Constipation   

  5. Headache        

  6. Loss of appetite

  7. Intestinal perforation and death may occur in severe cases.

  • Typhoid fever can be confirmed by widal test.

  • Mary Mallon called typhoid Mary, was a cook and a typhoid carrier who continued to spread the diseases for several years through the food prepared by the, before it was discovered.



  • It is caused by Streptococcus pneumoniae and Haemophilus influenzae.

  • They infect alveoli (air filled sacs) of the lungs where the alveoli get filled with a fluid resulting in the decrease of respiratory efficiency of the lungs.

  • It is spread by inhaling droplets or aerosols released by an infected person or even by sharing glasses and utensils with an infected person.



  1. Fever         

  2. Chills        

  3. cough         

  4. headache           

  5. In severe cases the lips and fingernails may turn Gray to bluish in colour.


Viral Diseases:

Common cold

  • It is caused by a group of viruses called Rhino viruses.

  • These viruses infect the nasal epithelium and respiratory passage but not the lungs.

  • Common cold usually last for about 3-7 days.


Mode of Transmission:

  1. It transmitted through contaminated objects like pens, books, cups, door knobs, computer key boards or mouse etc.,

  2. cough and sneeze droplets from an infected person.



  1. Nasal congestion and discharge

  2. Sore throat

  3. Hoarseness

  4. Cough

  5. Headache

  6. Tiredness


Dengue fever

  • It is caused by virus Flavivirus.

  • Dengue is transmitted by the bite of a mosquito infected with one of the four dengue virus serotypes.

  • It’s a febrile illness that affects infants, young children and adults with symptoms appearing 3-14 days after the infective bite.

  • There is no vaccine or any specific medicine to treat Dengue. People who have dengue fever should rest and drink plenty of fluids.



  1. High fever

  2. Severe headache

  3. Pain behind the eyes     

  4. Muscle and joint pain

  5. Rashes



  • It is caused by an alphavirus called Chikungunya virus.

  • It is generally spread through bites from Aedes aegypti mosquitoes.

  • The best means of prevention is overall mosquito control and the avoidance of bites by any infected mosquitoes.

  • No specific treatment is known, but medications can be used to reduce symptoms.



  1. Fever up to 104°F Severe

  2. joint pain

  3. Muscle pain

  4. Headache

  5. Nausea

  6. Fatigue

  7. Rash


Protozoan Diseases:


  • It is caused by a protozoan Plasmodium (P. vivax, P. malaria and P. falciparum).

  • P. falciparum causes the most serious and fatal malignant malaria.

  • The vector of Plasmodium is female Anopheles mosquito which transfers the sporozoites (infectious form).

  • Treatment is by antimalarial drugs like quinine, chloroquin.

  • Malaria can be prevented by killing mosquitoes by spraying DDT, BHC, etc, and using insect repellents, mosquito nets, etc.

  • Symptoms: Chills, fever, and sweating, usually occurring a few weeks after bitten.


Life cycle of Plasmodium

  • Plasmodium requires two hosts to complete its cycle – Mosquito and human.

  • The infected female Anopheles mosquito transfers the infectious form of Plasmodium, i.e., sporozoites to the human body by biting.

  • The sporozoites reach the liver cells, where they multiply.

  • This is followed by their attack on red blood cells resulting in their rupture.

  • The ruptured RBCs release a toxin called haemozoin, which is responsible for high recurring fever, chills and shivering.

  • These parasites enter the female Anopheles mosquitoes when they bite an infected person.

  • In the body of mosquitoes, they fertilize and multiply in the stomach wall.

  • Sporozoites are now stored in the salivary gland of mosquito till it is again transferred to human body by a mosquito bite. After entering the human body, all the events are repeated.

Plasmodium Life Cycle.png

Amoebic dysentery (Amoebiasis)

  • It is caused by an intestinal endoparasite, Entamoeba histolytica, found in large intestine of humans.

  • Housefly acts as mechanical carrier and transmits the parasite from faeces of infected person to the food.

  • Infection takes place through contaminated food and water



  1. Abdominal pain

  2. Constipation

  3. Cramps

  4. Stool with excess mucous and blood clots.

Fungal Diseases:


  • It is caused by fungi of genera Micrusporum, Trichophyton and Epidermophyton.

  • Human infection occurs either through contact with an infected person or from soil. It also spreads through towels, clothes, combs, etc., of the infected persons.



  1. Dry and scaly lesions on skin, nails and scalp.

  2. Lesions are accompanied by intense itching


Helminthic Diseases:


  • It is caused by an intestinal endoparasite of human, Ascaris lumbricoides, commonly called roundworm.

  • Eggs of parasite are excreted along with faeces of infected person, which contaminate water, soil and plants.

  • Infection takes place through contaminated vegetables, fruits and water.



  1. Abdominal pain

  2. Indigestion

  3. Internal bleeding

  4. Muscular pain

  5. Fever

  6. Anaemia

  7. Nausea and headache

  8. Blockage of the intestinal passage.



  • It is caused by filarial worms, Wuchereria bancrofti and Wuchereria malayi.

  • Female Culex mosquito is the vector.



  1. Inflammation of organs in which they live.

  2. Blockage of lymph vessels of lower limbs resulting in swelling. Lower limbs appear like legs of elephant, thus the name.

  3. Genital organs may also be affected, leading to deformation.


Prevention and Control of Infectious Diseases

The following measures can prevent/control the infectious diseases:

  1. Maintenance of personal hygiene by keeping the body clean, consuming clean drinking water, food, vegetables and fruits.

  2. Maintenance of public hygiene by proper disposal of wastes and excreta, periodic cleaning and disinfection of water reservoirs and pools.

  3. Eradication of vectors and their breeding places.

  4. Use of mosquito nets.

  5. Vaccination and immunization programmes for diseases like polio, diphtheria, tetanus, etc.

  6. Use of antibiotics and drugs to treat the infected person.



The overall ability of the host to fight the disease-causing organisms is called immunity.

Immunity is of two types:

  1. Innate immunity

  2. Acquired immunity


Innate immunity

  • It is present from the birth and is inherited from parents

  • It is non-specific type of defence.

  • It is accomplished by providing different types of barriers.


  1. Physical barriers: These barriers do not allow pathogens and foreign agents to enter the body, such as skin, mucous membranes of digestive, respiratory and urinogenital tracts trapping microorganisms.

  2. Physiological barriers: Sweat, tears, acid in the stomach and saliva prevent microbial growth.

  3. Cellular barriers: Certain types of leucocytes (WBCs) of our body like polymorpho-nuclear leukocytes [PMNL-neutrophils] and monocytes, natural killer (type of lymphocytes) and macrophages, phagocytose and destroy microbes.

  4. Cytokine barriers: Interferons produced by virus-infected cells protect non-infected cells from further viral infection.


Acquired immunity

  • It is not present from the birth and develops during an individual's lifetime.

  • It is pathogen specific.

  • It has the ability to distinguish diverse types of foreign molecules or antigens (specificity).

  • When the immune system encounters a pathogen for the first time, a primary response is produced which is of low intensity. The memory of this encounter with the same pathogen is also formed. On subsequent encounter with the same pathogen, a secondary or anamnestic response is produced which is of very high intensity.

  • Immune responses are produced by two types of lymphocytes:

  1. B-lymphocytes or B-cells produce an army of proteins called antibodies in blood, in response to pathogens.

  2. T-lymphocytes or T-cells help B-cells to produce antibodies.

  • Two types of acquired immune responses or immunities develop in the body:

  1. Humoral immune response or antibody mediated immunity (AMI): It is mediated by antibodies in the blood and lymph(humor).

  2. Cell-mediated immune response or cell-mediated immunity (CMI): It is mediated by T-lymphocytes. It is responsible for graft rejection in organ transplant because of its ability to differentiate between 'self' and 'non-self'.



Antibodies are protein molecules called immunoglobulins (Ig) and are of five types-IgA, IgM, IgE, IgG and IgD.

  • An antibody has a Y-shaped structure.

  • Each antibody molecule consists of four polypeptide chains, two are long called heavy (H) chains while the other two are short called light (L) chains. Hence, an antibody is represented as H2L2.

  • IgG is the most prevalent antibody in the blood followed by IgA and IgM.

  • IgA is present in breast milk (colostrum).

Antibody Molecule.png

Vaccination and Immunisation

  1. Vaccination is the process of introduction of weakened or inactivated pathogens or proteins (vaccine) into a person to provide protection against a disease.

  2. Immunisation is the process by which the body produces antibodies against the vaccine (primary response) and develops the ability to neutralise pathogens during actual infection (secondary response).

  3. Vaccination provides immunisation after a time gap.

  4. Vaccination and immunisation are based on the property called 'Memory' of the immune system.

  5. The vaccine generates memory B- and T-cells that recognise the pathogen on subsequent exposure and produce an intense immune response.

  6. If a quick immune response is needed as in tetanus infection, preformed antibodies or antitoxin injected into the patient. This type of immunisation is called passive immunisation.

  7. By recombinant DNA technology, vaccines have been produced on large scale, e.g., hepatitis-B vaccine is produced from yeast.


  • The exaggerated or hypersensitive reaction of the immune system to certain antigens present environment is called allergy.

  • The substances/agents to which an immune response is produced in an individual are called allergens. E.g., pollen grains, animal dander, dust, feathers, drugs like penicillin, etc.

  • IgE antibodies are produced in response to allergens.

  • Causes: Chemicals like histamine and serotonin released from the mast cells.


  1. Sneezing

  2. Watery eyes

  3. Running nose

  4. Difficulty in breathing.

  • Drugs like anti-histamine, adrenalin and steroids quickly reduce the symptoms of allergy.


Auto Immunity

  • It is an abnormal immune response in which the immune system of the body starts rejecting its own body cells or 'self' cells and molecules.

  • For example, rheumatoid arthritis, Addison's disease.


Immune System

The Human immune system consists of:

  • Lymphoid organs

  • Immune cells

  • Soluble molecules like antibodies

  • Lymphoid tissues


1. Primary lymphoid organs:

The organs where lymphocytes originate and mature to become antigen-sensitive, e.g., bone marrow and thymus, are called primary lymphoid organs.


a. Bone marrow-

  • It is the primary lymphoid organ where all blood cells including lymphocytes originate.

  • Bone marrow provides the micro-environment for the development and maturation of B-lymphocytes.


b. Thymus-

  • Thymus is a lobed organ located near the heart and beneath the breastbone.

  • It is quite large at the time of birth but reduces with age.

  • It provides the micro-environment for the development and maturation of T-lymphocytes.


2. Secondary lymphoid organs:

  • The organs where lymphocytes interact with the antigen and proliferate to become effector cells, e.g., spleen, lymph nodes, tonsils, Peyer's patches of small intestine and appendix are called secondary lymphoid organs.


a. Spleen-

  • It is a large bean-shaped organ and contains lymphocytes and phagocytes.

  • It acts as a filter of the blood by trapping blood-borne micro-organisms.

  • It has a large reservoir of erythrocytes.


b. Lymph nodes-

  • These are small solid structures present at different points along the lymphatic system.

  • They trap the microorganisms or other antigens that enter the lymph and tissue fluid.

  • Antigens trapped in the lymph nodes activate the lymphocytes and produce an immune response.


c. Mucosal associated lymphoid tissue (MALT)-

  • It is formed of masses of lymphoid tissue lining the mucosa of respiratory, digestive an urinogenital tracts.

  • 50 per cent of the lymphoid tissue in human body is formed by MALT.

Immune system

Acquired Immuno Deficiency Syndrome (AIDS)

  • It was first reported in U.S.A. in 1981.

  • In India the first AIDS patient was officially identified in 1987 at Chennai.

  • It is caused by the Human Immunodeficiency Virus (HIV). HIV belongs to the group retrovirus.

  • It has RNA genome enclosed in a protein envelope.


Transmission of HIV occurs through following ways:

  1. By sexual contact with the infected person.

  2. By transfusion of contaminated blood and blood products.

  3. By sharing infected needles.

  4. From infected mother to her child through placenta.


High risk individuals:

  • Those having multiple sexual partners.

  • Drug addicts taking the drugs intravenously.

  • Individuals who require repeated blood transfusions.

  • Children born to an HIV infected mother.


Diagnosis is done by enzyme linked immunosorbent assay (ELISA).

Preventive measures:

  • National AIDS Control Organisation (NACO) established in 1991 and other non-governmental organisations (NGOs) educate people about AIDS.

  • WHO has started a number of programmes to prevent the spreading of HIV infection that includes:

  1. Making blood from blood banks safe from HIV.

  2. Ensuring the use of only disposable needles and syringes.

  3. Free distribution of condoms.

  4. Controlling drug abuse.

  5. Advocating safe sex and promoting regular check-ups.


Life cycle of HIV:

  • After getting into the body of a person, the virus enters the macrophages.

  • Here, RNA is replicated to form viral DNA by enzyme reverse transcriptase.

  • The viral DNA now gets incorporated into the host cell's DNA and directs the infected cells to produce viruses.

  • The macrophages continue to produce virus particles.

  • The virus particles enter helper T-lymphocytes (TH cells) in the blood, where they continue to replicate and produce viral progenies.

  • Thus, the number of helper T-lymphocytes progressively decreases in the body of the infected person.

  • With the decrease in number of T-cells, the immunity also decreases. The person is unable to produce any immune response even against common bacteria like Mycobacteriem, parasites like Tixoplasma, viruses and fungi.

HIV lifecycle.png


Cancer is defined as an uncontrolled division or proliferation of cells without any differentiation.

 Characteristics of cancer cells:

  • The cells divide repeatedly with uncontrolled cell division.

  • The cancer cells do not require extracellular growth factors.

  • Cancer cells have lost the property of contact inhibition.

  • Due to repeated division, cells form a large mass of tissue called tumor.

  • The cells pass out from the tumor to new sites for forming secondary tumors.

  • Tumors are of two types- -benign and malignant.

  • Benign tumors normally remain confined to their original location and do not spread to other parts of the body and cause little damage.

  • The malignant tumors are a mass of proliferating cells called neoplastic or tumor cells.

  • The invasion of cancerous neoplastic cells from one part to the other parts through body fluid is called metastasis.


Causes of cancer

  • The cancer-causing agents are called carcinogens.

  •  Cancer-causing viruses are called oncogenic viruses have genes called viral oncogenes.

  • Several genes called cellular oncogenes (e-onc) or proto-oncogenes, have been identified in normal cells, present in inactivated state but under certain conditions (like mutation) get transformed to cancer-causing oncogenes.

  • Carcinogens are of following types:

  1. Chemical agents: Aniline dyes, N-nitrosodimethylamine, benzopyrene, chemicals in cigarette smoke.

  2. Physical agents: Ionising radiations like X-rays and gamma-rays, non-ionising radiations like UV-rays.

  3. Biological agents: Oncogenic viruses, some parasites.


Types of cancer

  1. Carcinoma: It is cancer of epithelial tissue, e.g., skin cancer

  2. Melanoma: It is cancer of melanocytes of skin.

  3. Sarcoma: It is cancer of mesodermal tissue.

  4. Leukemia and lymphoma: It is cancer of haemopoietic cells (blood cells).


Cancer detection

  1. Blood and bone marrow tests: are done for increased cell counts in case of leukemia.

  2. Histopathological study or biopsy: In biopsy, a piece of the suspected tissue cut into thin sections is stained and examined under microscope by a pathologist.

  3. Radiography: X-rays are used to detect cancer of the internal organs.

  4. Computed tomography (CT scanning): It uses X-rays to generate a three-dimensional image of the internal of an object.

  5. Magnetic resonance imaging (MRI): Non-ionising radiation and strong magnetic field are used in MRI to accurately detect pathological and physiological changes in the living tissue.

  6. Monoclonal antibodies: Antibodies against cancer-specific antigens are also used for detection of certain cancers.


Cancer treatment

  • The common approaches for treatment of cancer are:

  1. Surgery: The tumor cells are removed with the help of surgery to check the spread of cancerous cells.

  2. Radiation therapy: A lethal irradiation of tumor cell is done, taking proper care of the normal tissues surrounding the tumor mass.

  3. Chemotherapy: Cancerous cells are killed by several chemotherapeutic drugs. These drugs exhibit side effects like hair loss, anaemia.

  4. Immunotherapy: In this method, biological modifiers like α-interferons are used which activate the immune system and help in destroying the tumor.


Drugs and Alcohol Abuse:

When drugs and alcohol for taken for purposes other than medicinal or taken in amounts or frequencies that impairs physical, physiological or psychological functions, it is called drug abuse and alcohol abuse, respectively.

Drugs belong to different categories which are as follows:

1. Opioids:

  • Heroin is commonly called smack is chemically diacetylmorphine which is a white, odourless, bitter crystalline compound.

  • Source: Morphine is extracted from the latex of poppy plant Papaver somniferum.

  • Mode of intake: By snorting and injection.

  • Mode of action: They bind to specific opioid receptors in the central nervous system (CNS) and gastrointestinal tract.

  • Effects: Heroin is a depressant and slows down body functions. Morphine is an effective sedative and painkiller


2. Cannabinoids:

  • Source: Obtained from inflorescence of the plant Cannabis sativa. Flower tops, leaves and resins of C. sativa in various combinations produce hashish, charas, marijuana and ganja.

  • Mode of action: Cannabinoids interact with cannabinoid receptors present in the brain.

  • Mode of intake: By inhalation and oral ingestion.

  • Effects: Effect the cardiovascular system of the body.


3. Coca alkaloids or cocaine:

  • Source: Derived from the leaves and young branches of South American plant called Erythroxylum coca.

  • Mode of intake: By sniffing and snorting.

  • Mode of action: It has a potent stimulating action on central nervous system and interferes with the transport of neurotransmitter dopamine.

  • Effects: It is a strong stimulant and when take in overdose cause headache, convulsions, hallucinations and death due to cardiovascular or respiratory failure.


4. Hallucinogens:

  • Source: Obtained from plants like Atropa belladonna and Datura sps. Lysergic acid diethylamide (LSD) is derived from the fungus Claviceps purperea.

  • Mode of action: These drugs are called psychedelic drugs because of their effect on cerebrum and sense organs.

  • Effects: These drugs effect thoughts, feelings and perceptions of an individual. Medically these are given to patient to cope with mental illness like a depression and insomnia  

  • g., Barbiturates, amphetamines, benzodiazepines.


5. Tobacco:

  • Source: Tobacco plant.

  • Mode of intake: It is smoked, chewed or used as a snuff.

  • Mode of action: It has nicotine which stimulates the adrenal gland to release adrenaline and noradrenaline which in turn increases the blood pressure and heart rate.

  • Effects:

  1. It increases the chances of lung cancer, bronchitis, emphysema, coronary heart disease, cancer of throat, gastric ulcer, cancer of urinary bladder, etc.

  2. Smoking leads to increase in carbon monoxide content of blood and reduces concentration of haem-bound oxygen, as a result of which oxygen deficiency in the body is created.

  3. Chewing of tobacco causes oral cancer which becomes fatal in extreme conditions.


6. Alcohol:

  • Mode of intake: Oral intake.

  • Mode of action: Alcohol has an anaesthetic effect on nervous system affecting cerebrum, cerebellum and other parts.

  • Effect: It may cause euphoria, peptic ulcer, gastric carcinoma, hepatitis, liver failure, liver cell carcinoma.


Addiction and Dependence

  • The psychological attachment to certain effects such as euphoria and temporary feeling of well- being, associated with drugs and alcohol is called addiction.

  • Reasons for alcohol abuse in adolescents:

  1. Social pressure.

  2. Curiosity and need for adventure, excitement and experiment.

  3. To escape from stress, depression and frustration.

  4. To overcome hardships of daily life.

  5. Unstable or unsupportive family structure.

  • The tendency of the body to manifest characteristic and unpleasant withdrawal syndrome on abrupt discontinuation of regular dose of drugs/alcohol is called dependence.

  • Characteristics of withdrawal symptoms: Anxiety, Shakiness, Nausea, Sweating, Vomiting, Diarrhoea, Insomnia, Restless, Muscular and abdominal cramps.


Effects of Drug and Alcohol Abuse:

  • Alcohol has an anaesthetic effect on nervous system, affecting cerebrum followed by cerebellum and other parts.

  • It affects the nervous system in following ways:

  1. Loss of judgement will power and self-control.

  2. Loss of emotional control.

  3. Loss of moral sense.

  4. Visual problem.

  5. Staggering and incoherent speech.

  6. Inflammation of axon of neuron leading to neuritis.


Side effects of drugs on males: Acne, aggressiveness, reduction in size of testicles, decreased sperm production, premature baldness, enlargement of prostate gland.


Side effects of drugs on females: Masculinisation, aggressiveness, mood swings, depression, abnormal menstrual cycles, enlargement of clitoris and excessive facial and body hair.


Warning signs of drug and alcohol abuse:

  1. Drop in academic performance.

  2. Absence from school/college.

  3. Lack of interest in personal hygiene.

  4. Isolation, depression, fatigue, aggressive and rebellious behaviour.

  5. Deteriorating relationships with family and friends.

  6. Fluctuation in weight, etc.

  • Those who take drugs intravenously develop a risk of AIDS and hepatitis-B.

  • Use of alcohol during adolescence may lead to heavy drinking in adulthood.

  • The chronic use of drug and alcohol damages nervous system and liver (cirrhosis) and the alcoholism during pregnancy affects the foetus.


Prevention and Control:

  1. Avoid undue peer pressure.

  2. Educating and counselling the problems and stresses to avoid disappointments and failures in life.

  3. Seeking help from parents and peers.

  4. Looking for danger signs to take appropriate measures on time.

  5. Seeking professional and medical help whenever required.

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