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HUMAN HEALTH AND DISEASE

INTRODUCTION

  • Health is a state of complete physical, mental and social well being, and not merely an absence of disease or infirmity (W.H.O - 1948).
  • Any change from the normal state that causes discomfort or disability or impairs the health is called disease.
  • Time interval between the entry of pathogen and appearance of symptoms is called the incubation period. During this period, pathogens multiply.
  • Antibiotics are those substances which are secreted by micro-organism that inhibit the growth or destroy the other micro-organism. This term was given by Walksman (streptomycin-first bacterial antibiotic obtained from bacteria-Streptomycin griseus).
E.g., Bacteriostatic - tetracycline, chloramphenicol,
Bacteriolytic or Bactericidal-streptomycin, ciprofloxacin, ampicillin.
  • Antiseptics and disinfectants are agents that inhibit or kill microbes on contact. Conventionally, agents used on living surfaces are called antiseptics while those used for inanimate objects are called disinfectants.
In disinfection, it kills only vegetative forms of bacteria.
  • Sterilization is the process that kills all forms of pathogens, including spores.
  • The disease agent is a factor (substance or force) which causes a disease by its excess or deficiency or absence.
  • Types of disease agents are biological, nutrient, chemical, physical, mechanical etc.
  • Biological agents - It includes viruses, rickettsias, bacteria, fungi, protozoans, helminthes and arthopods. 
    • The biological agents are called pathogens (Gr. Pathos = disease; genes = producing).
    • Pathogens produce diseases in two ways : tissue damage and toxin secretion.
    • Tissue damage : The bacteria responsible for tuberculosis, damage cells and cause lesions in the lungs. Blood oozes from the lesions into the air sacs, leading to haemorrhages. The bacteria that cause meningitis attack the protective membranes covering the brain. The virus of rabies destroys brain tissue. The polio virus damages motor nerve cells in the spinal cord.
    • Toxin secretion : Many microbes produce powerful poisons, called toxins, which cause diseases. 
    • Toxins are of 2 types : endotoxin and exotoxin.
    • Exotoxins are released as soon as produced. The diseases brought about by exotoxins include tetanus, scarlet fever, diphtheria, and botulism (food poisoning).
    • Endotoxins are retained in the bacterial cells and released when bacteria die and disintegrate. The diseases caused by endotoxins include typhoid fever, cholera, bubonic plague and dysentery.
  • Nutrient agents 
These comprise food components such as carbohydrates, fats, proteins, minerals, vitamins and  water.
  • Chemical agents
    • These are further of two types - endogenous and exogenous.
    • Endogenous chemical agents are formed in the body itself and include hormones, enzymes, urea and uric acid.
    • Exogenous chemical agents enter the body from outside by inhalation, ingestion or inoculation. Pollutants (fumes, gases, dusts, metals) and allergens (spores, pollen) are examples.
  • Physical agents
These include heat, cold, humidity, pressure, radiation, electricity and sound.
  • Mechanical agents
These comprise chronic friction or other mechanical forces which result in injury, sprain, dislocation, fracture.
  • Deficiency and excess of substances : e.g., hormones, enzymes.
  • Some diseases are caused by genetic disorders and lack or underdevelopment of organs. The agents for certain diseases such as peptic ulcers, coronary heart diseases and hypertension, are not fully known.

Table : Medical Terms 

SCIENTISTS

  • Father of Medicine : Hippocrates. He gave a scientific explanation of disease for the first time.
  • Father of Surgery: Susruta. He used non-poisonous leeches as an anticoagulant during surgery.
  • Father of Ayurveda : Charaka (Ayu → Life, Veda → Knowledge). He first gave concept of digestive, metabolism and immunity.
  • Father of Modern Pathology : Rudolf  Virchow.
  • Father of Immunity : Edward Jenner (Smallpox vaccine).
  • Father of Blood grouping : C. Landsteiner.
  • Father of Modern Bacteriology : Robert Koch (Anthrax, T.B., Cholera)
  • Nobel Prize for odorant receptor (olfaction) is given to Richard Axel and Linda B.Buck.

TYPES OF DISEASES

  • The diseases may be broadly classified into two types : congenital and acquired.
  • Congenital Diseases are anatomical or physiological abnormalities present from birth. They may be caused by –
    • A single gene mutation (alkaptonuria, phenylketonuria, albinism, sickle-cell anaemia, haemophilia, colour blindness). 
    • Chromosomal aberrations (Down’s syndrome, Klinefelter’s syndrome, Turner’s syndrome) or 
    • Environmental factors (cleft palate, harelip). 
  • Unlike the gene and chromosome-induced congenital defects, environmentally caused abnormalities are not transmitted to the children.
  • Acquired Diseases develop after birth. They are further of two types : communicable and non-communicable.

COMMUNICABLE DISEASES 

  • The diseases which are caused by pathogens (viruses and living organisms) and readily spread from the infected to the healthy persons are called communicable or infectious diseases.
  • A German physician, Robert Koch, listed the following four conditions to establish that a specific pathogen causes a particular disease –
    • The suspected pathogen should be invariably present in the animals suffering from the disease and should not be found in healthy individuals.
    • The pathogens isolated from the diseased animal should be grown in a pure culture. 
    • When this culture is inoculated into a healthy host, the latter should develop the disease and show its characteristic symptoms.
    • The pathogen should be recoverable from the experimental host, and it should be the same as the original one. 

TRANSMISSION OF DISEASES (PATHOGENS)
  • The diseases (pathogens) are transmitted from the reservoirs of infection to the healthy persons in the following ways : direct and indirect transmission.
  • Direct transmission : The pathogens of some diseases reach the human body directly without intermediate agents. This can occur as under :
    • Contact with Infected Persons : Certain diseases produce sores or lesions on the skin. Contact with materials discharged from these sores or lesions brings about infection. Ringworm, athlete’s foot, barber’s itch, chickenpox, smallpox, syphilis and gonorrhoea are spread by direct contact. Kissing also spreads infection. The diseases that are transmitted by direct contact are called contagious diseases.
    • Droplet Infection : Some diseases are caught by merely being in a confined place (room, theatre, bus) with an infected person. The latter throws out tiny droplets of mucus by coughing, sneezing, spitting or even talking. These droplets may contain pathogens (viruses, bacteria) dislodged from nasal membrane, throat, and lungs. Many of these droplets are inhaled. Diphtheria, scarlet fever, influenza, common cold, measles, mumps, tuberculosis, pneumonia, and whooping cough are spread by droplets.
    • Contact with Soil : The bacteria responsible for tetanus and blood poisoning enter the human body from the soil through injuries. Hence, skin injuries should not be neglected. 
    • Animal Bites : Virus of rabies, or hydrophobia, is introduced through the wound caused by the bites of rabid animals, most commonly dogs.
    • Through Placenta : In the later part of pregnancy, due to age or injury, the placenta becomes permeable to certain pathogens such as virus of german measles and bacteria of syphilis. The pathogens then pass from the maternal blood into the foetal blood.
  • Indirect Transmission : The pathogens of certain diseases reach the human body through some intermediate agents. These agents are - 
    • Vectors : Insects transmit diseases in two different ways -
Housefly carries the causative organisms of cholera, typhoid, dysentery and tuberculosis on the legs and mouth parts from faeces and sputum to food and drinks. The latter, if taken, cause infection. It also carries the microbes responsible for ophthalmia and conjunctivitis from eye to eye. Ants, cockroaches and house crickets also carry disease germs to articles of food.
Certain blood-sucking insects carry disease-causing organisms in their body and transmit them with bites. Human body-louse spreads typhus, rat flea transmits bubonic plague, tsetse fly spreads African sleeping sickness, sandfly transmits kala-azar and oriental sore, Aedes mosquito spreads yellow fever, Culex mosquito transmits filariasis, and Anopheles mosquito spreads malaria, ticks spread rocky mountain spotted fever.
    • Vehicle-borne Method : The causative organisms of dysentery, cholera and typhoid enter the human digestive tract with food and water. Most of the helminthes which produce diseases in man also get into the body in a similar way. Some diseases are transmitted through blood, e.g., AIDS.
    • Air-borne Method : The pathogens may reach the humans with air and dust. The epidemic typhus spreads by inhalation of dried faeces of infected lice.

CLASSIFICATION OF COMMUNICABLE DISEASE

Depending upon the type of causative agent, communicable diseases are the following types - bacterial, viral, rickettsial, spirochaetal, protozoan, fungal and helminthes etc.

BACTERIAL DISEASES
Types of bacterial diseases are cholera, pneumonia, typhoid etc.

Table : Bacterial Diseases in Human

VIRAL DISEASES
Viral diseases are transmitted by contact fomite and droplet method. Types of viral disease are-influenza, small pox, etc.

Table : Viral Diseases in Humans

PROTOZOAN DISEASE
These are caused by protists. They include malaria, amoebiasis, giardiasis, kala azar, Ciliary dysentery, trypanosomiasis etc.

(a) Malaria
  • Laveran (1880) discovered malarial parasite in blood of malaria patient.
  • Pfeiffer (1892) proposed that malaria is spread by blood sucking insect.
  • Discovery of Plasmodium and its transmission  by Anopheles (female) was confirmed by Ronald Ross (1897).
  • Malaria is caused by the toxins produced in the human body by the malarial parasites, Plasmodium.
  • The malarial parasites are carried from the infected to the healthy persons by the female Anopheles mosquito. The mosquito picks up the parasites with the blood, when it bites an infected person. When this infected mosquito bites a healthy person, parasites migrate into his blood with the saliva, which the mosquito injects before sucking up blood to prevent its clotting.
Fig. : Stages in the life cycle of Plasmodium
  • There are four species of Plasmodium, which cause different kinds of human malaria
    • P. vivax : It causes benign tertian malaria, which attacks every third day, i.e., after 48 hours. The fever is mild and seldom fatal. This species is wide-spread in the tropical and temperate regions.
    • P. ovale : It also causes benign tertian malaria, which recurs every 48 hours. This species is found only in West Africa and South America.
    • P. malariae : It causes quartan malaria, which recurs every fourth day, i.e., after 72 hours. This species is found in both tropical and temperate regions, but it is not very common.
    • P. falciparum : It alone is capable of causing three types of malaria, viz., quartan malaria, which attacks almost daily, malignant tertian malaria, which occurs every 48 hours, but is very severe and often fatal; and irregular malaria. This species is found only in the tropical region.
  • Malaria result in anaemia, toxaemia and splenomegaly (enlarged spleen).
  • Antimalarial drugs are quinine, chloroquine etc. Dalaprim drug kills the parasitic stages present in both liver cells and RBC's of blood.

(b) Amoebiasis
  • It is caused by intestinal endoparasitic protozoan Entamoeba histolytica of man.
  • Infection is transmitted by contamination.
  • It is characterized by abdominal pain alternating diarrhoea and constipation etc.
  • Entamoeba secretes cytolysin that erodes the mucous membrane of the intestine.

(c) Giardiasis
  • Also called backpeper's disease, it is caused by Giardia intestinalis.
  • It inhabits upper part of small intestine (duodenum and jejunum)
  • Infection is transmitted by contamination of cysts with food and drinks.
  • It is characterized by mild diarrhoea.

(d) Kala azar
  • Kala azar or leishmaniasis is caused by Leishmania donovani and spread by sandfly (Phlebotomus)
  • It is characterized by fever and enlargement of visceral organs.
  • It is also known as dum-dum fever
  • Leishmania braziliensis causes espundia and oriental sore is caused by L.tropica.

(e) Ciliary dysentery (Balantidiasis)
  • It is caused by Balantidium coli. It inhabits the human large intestine (colon).
  • Infection occurs by ingesting cysts with food and drinks.
  • Balantidium coli causes ulcers in the colon and invades mucous membrane by secreting an enzyme hyalurodinase. Thus, generally results in diarrhoea.
  • Tetracycline or lodoquinol are effective treatment.

(f) Trypanosomiasis
  • It is caused by different species of Trypanosoma.
  • It is characterized by high fever, swelling of the neck and armpit, weakness, anaemia, lethargy, unconsciousness etc.
  • T. gambiense causes Gambian fever of West African sleeping sickness, which is spread by both sexes of tse-tse fly (Glossina palpalis).
  • Rhodesian or East African sleeping sickness, caused by T. rhodesiense is spread by G. morsitans. Chagas disease or South American sleeping sickness is caused by T. cruzi and spread by Panstrongilus sp. It is more common in children and young adults.
Table : Sexually Transmitted Diseases (STD) in Human

HELMINTHIC DISEASES
Helminthes are multicellular parasites and includes roundworms and flatworms. Helminthes causes various diseases in man like, filariasis, taeniasis, ascariasis, enterobiasis etc.

(a) Filariasis
  • It is caused by Wucheria bancrofti. It is also known as elephantiasis due to excessive enlargement of body parts like leg.
Fig. : Diagram showing inflamation in one of the  lower limbs due to elephantiasis
  • Symptoms include fever, proliferation of endothelial cells and deposition of metabolites in the wall of lymph vessels.
  • It is transmitted by Culex or Aedes mosquitoes.

(b) Taeniasis
  • It is caused by intestinal endoparasite, Taenia solium.
  • It is characterized by abdominal pain, indigestion, loss of appetite, nausea etc.
  • Cysticercosis larva of Taenia causes cysticercosis which causes damage to different body parts, blindness etc.

(c) Ascariasis
  • It is caused by Ascaris lumbricoides.
  • Vectors for this disease are flies and cockroaches.
  • It is characterized by colic pain, indigestion, diarrhoea, vomiting, weakness etc.
  • Scratch test, dermal test and stool test can be done to detect the roundworm infection.

(d) Enterobiasis (oxyuris)
  • It is caused by Enteriobius vermicularis (pin or seat worm).
  • Its transmission is direct by contaminated food.
  • It causes anal itching, appendicitis, nervous problem. 

(e) Ancylostomiasis
  • It is caused by Ancylostoma duodenale.
  • It is transmitted by infected larva via contaminated food and vegetables.
  • Symptoms include chronic blood loss, depletion of body's iron stores leading to anaemia, inflammation of skin etc.

(f) Schistosomiasis (Bilharzia)
  • It is caused by Schistosoma haematobium.
  • It is transmitted by snail.
  • It is found in urinary bladder, blood vessels and causes itching, rashes, aches, fever etc.

FUNGAL DISEASES
These are caused by fungi, the non green heterotrophic organisms. They include ringworm and athlete's foot.

(a) Ringworm 
  • Ringworm is caused by different genera of fungi - Microsporum, Trichophyton and Epidermophyton.
  • It is an infection of skin, hair and nails.
  • Its symptoms includes red scaly patch or bump.
  • Ringworm is contagious and is easily spread from one person to another, so avoid touching an infected area on another person. 

(b) Athletes foot
  • It is caused by a fungus called Tinea pedis.
  • It is a very common skin condition that affect the sole of the foot and the skin between the toes.
  • Common symptoms include various degrees of itching and burning.

NON COMMUNICABLE (NON-INFECTIOUS) DISEASES
  • These diseases remain confined to the person who develops them and do not spread to others.
  • The main non-communicable diseases are diabetes, inflammatory diseases of joints such as arthritis, gout, cardiovascular diseases and cancer.

(a) Diabetes Mellitus 
  • Diabetes is characterized by chronic hyperglycemia which is excessive concentration of glucose in the blood.
  • Diabetes is primarily a result of relative or complete lack of insulin secretion by the β cells of islets of Langerhans in pancreas.
  • Diabetes is established by blood and urine sugar levels.

(b) Arthritis
  • Arthritis is any inflammatory condition of the joints characterized by pain and swelling.
  • Types of arthritis are : rheumatoid arthritis, osteoarthritis and gout.
  • There is no cure for arthritis, drugs are available which relieve pain.
  • Rheumatoid arthritis 
    • It is characterized by inflammation of the synovial membrane.
    • A kind of rheumatoid arthritis that occurs in younger people is Still’s disease.
    • It usually starts in the small joints in the hand and progress to other body joints.
  • Osteoarthritis 
    • It is a common disease among the elderly persons resulting from erosion of articular cartilage.
    • In osteoarthritis, the secretion of lubricating synovial fluid between the bones at the joint stops. The joints become inflammed, its movement becomes painful and its function is diminished.
    • It is common in old person, mainly affecting weight bearing joints.
  • Gout
    • Gout results from accumulation of uric acid crystals in the synovial joints.
    • Gout is a disease associated with an inborn error of uric acid metabolism that increases production or interferes with excretion of uric acid.
    • It is very painful, particularly at night and make movement difficult. Gout generally affects the great toe.

CARDIOVASCULAR DISEASES
  • Cardiovascular diseases refer to a number of diseases associated with the blood vascular system.
  • Some major cardiovascular diseases are rheumatic heart disease, hypertensive heart disease and coronary heart disease.
  • Rheumatic heart disease
    • Rheumatic heart disease is an autoimmune disease, most common in children after a severe throat infection by certain strain of Streptococcus bacteria.
    • An antigen on the surface of these bacteria is very similar to an antigen on the surface of myocardium.
    • The antibodies against Streptococcus may react with myocardium and cause heart difficulties.
  • Hypertensive heart disease
    • Hypertensive heart disease are caused by hypertension, i.e., increased blood pressure.
    • Serious hypertension is a common cause of chronic heart failure particularly in older people. 
  • Coronary heart diseases 
    • Coronary heart diseases are characterized by impaired heart function due to inadequate blood flow to the heart. Angina pectoris is the chest pain caused most often by myocardial anoxia. 
    • Attacks of angina pectoris are often related to exertion, emotional disturbance and exposure to excess cold. 
    • Myocardial infarction is commonly called coronary or heart attack. 
    • Coronary heart disease may be due to raised serum cholesterol, cigarette smoking, high blood pressure, physical inactivity, obesity and diabetes.
    • Cyanosis refers to a bluish coloration of the skin and mucous membranes due to too much deoxygenated haemoglobin in the blood. 
  • Stroke
    • It is the most common degenerative disease in man.
    • It is a brain damage due to stoppage of blood supply resulting from cerebral thrombosis, cerebral haemorrhage etc.
    • It is characterized by degeneration of motor nerves of brain due to reduced supply of oxygen resulting in paralytic attack of some body parts especially limb, loss of memory, speech and even death.

IMMUNE SYSTEM

  • System which protects the body from diseases is called immune system.
  • The immune system consisting of several organs as well as WBC in blood and lymph has the job of fighting off invading pathogens and preventing growth and spread of cancers.
  • Lymphoid organs are those organs where origin and maturation and proliferation of lymphocyte occurs.
  • The primary lymphoid organs are bone marrow and thymus.
  • Bone marrow manufactures billions of WBC needed by the body everyday. Some newly produced WBC remain in the bone marrow to mature and specialize while others travel to the thymus to mature.
  • Secondary lymphoid organs includes lymph node, adenoids tonsils, spleen, peyer's patches (within intestine) and the appendix.
  • Lymph nodes filter pathogens from the lymph and exposes them to WBC.
  • Spleen filters pathogens from blood. It is stocked with WBC that respond to the trapped pathogen.
  • Lymphoid tissue located within the lining of the major tracts (respiratory, digestive and urogenital tracts) is called mucosal associated lymphoid tissue (MALT). It constitutes about 50% of the lymphoid tissue in human body.
  • Immunology is the science of development of immunity against particular pathogen.
  • The foundations of science of immunology were discovered by workers-Edward Jenner (1796), Louis Pasteur (1879) and Von Behring (1841). 
  • Some terms related to immune system are –
    • Immunity: Resistance of the body against a pathogen or disease.
    • Antigen or Agglutinogen : Proteinous substance which stimulates the production of antibodies.
    • Antibody : It is a complex glycoprotein secreted by
      B-lymphocytes in response to an antigen. It is also called agglutinin. 
    • Antiserum: Serum of any animal which contains the antibody for a specific antigen.
    • Venom (poison) : Toxic substances secreted by snake and some insect. 
    • Toxoid: A bacterial exotoxin which is detoxicated by special procedures to allow its safe use in immunization against the disease.
  • Immunity was defined by Sir Mac Farlane Burnet.
  • Immunity developed in 3 ways-by vaccination, antitoxin and through disease.
  • Immunity are of two types-
    • Congenital immunity or innate immunity or Non-specific immunity
    • Acquired immunity or Adaptive or specific immunity
  

INNATE OR NON SPECIFIC IMMUNITY

  • Innate immunity, present from birth, are specific (acts on many organism) and does not become more efficient on subsequent exposure to the same organism.
  • The non-specific defence mechanisms is further of two types-external defence (first line of defence) and internal defence (second line of defence) 
  • First line of defence comprise physical and chemical barriers to the entry of pathogens into the blood.
  • Physical barrier includes skin and mucous membrane and chemical barriers includes chemicals secreted by skin and mucous membrane like skin secretion and bacteria, nasal secretion, cerumen (ear wax), saliva, tear, vaginal bacteria.
  • Acid in stomach, saliva in mouth, tears from eyes, all prevent microbial growth.
  • Second line of defence/internal defence is carried out by WBC, macrophages, inflammatory reactions, fever, interferons and complement system.
  • Inflammatory response is a reaction that causes redness, heat, swelling and pain in the area of infection.
  • Body temperature rise causes fever, fever is caused by the release of chemical called pyrogen from damaged tissues.
  • Interferons (discovered by Issacs and Lindermann) are produced against viral infection.
  • The complement system plays an important role in host defence against infectious agents and in the inflammatory response.

ACQUIRED IMMUNITY

  • It is the resistance that an individual acquires during life. This is generated in response to an exposure to the microorganism in question.
  • This type of immunity is found only in vertebrates.
  • It is also called adaptive or specific immunity.
  • This immunity is acquired after birth by experience.
  • This immunity recognise and selectively eliminate the pathogen.

FEATURES OF ACQUIRED IMMUNITY
  • Specificity : Acquired immunity is specific for specific microorganisms.
  • Diversity: This system recognises the vast variety of microorganisms.
  • Discrimination between self and non-self : It can recognise self (body or tissue) and non-self (foreign tissue) and respond according to them.
  • Memory: When a pathogen enter inside the body, body takes longer time to recognise and respond to it. This is called primary immune response but the memory of this encounter remain in immune system.
    When this pathogen enters second time inside the body, the body's immune system rapidly recognises this pathogen and responds quickly to it. This is called secondary immune response. This is based on memory of the immune system.

TYPES OF ACQUIRED IMMUNITY
  • Active acquired immunity : Resistance developed by an individual as a result of an antigenic stimulus.
Natural : Results from a clinical or inapparent infection by a microorganism.
Artificial : Resistances induced by vaccine.
Vaccines are prepared by live or killed microorganisms or their products and is used for immunisation.
  • Passive immunity : It is received passively by host without participation or contribution from host's immune system. Immunological memory is absent here and the readymade antibodies are given in immunosuppressive individual. 
Natural : Resistance passively transferred from mother to baby. Mother milk gives passive immunity to the newborn child by colostrum (first mother milk).
Artificial:  Resistance passively transferred to a recipient by administration of antibodies.
E.g. : Human immunological administration.
Anti - Tetanus serum (ATS)
Anti - rabies serum (ARS)
Anti - diptheria serum (ADS)

Table : Difference between Active and Passive immunity

TYPES OF ACTIVE IMMUNE SYSTEM

CELL MEDIATED IMMUNE SYSTEM (CMIS) OR CELLULAR IMMUNITY 
This immune system is based on T-cells (60-70%) with antigen specific receptors on their surfaces.

Table : Cells of Immune System

ANTIBODY MEDIATED IMMUNE SYSTEM (A.M.I.S.) OR HUMORAL IMMUNITY
  • Antibody or immunoglobulin are complex glycoprotein molecule made up of 4 polypeptide chains-two light and two heavy chains.
  • These two chain held together by disulphide bond in shape of Y molecule.
Two tips of this molecule bind with antigen (large and complex foreign molecules mainly proteins that activate the specific immunity) like lock and key fashion and make antigen-antibody complex.
 Fig. : Structure of an antibody molecule
  • Precipitation : Antibodies combine with the antigens to form precipitates that are early ingested by the phagocytes. They are known as precipitins.
  • Complement activation : Antibody antigen complexes activate complement proteins which may opsonise antigen, lyse cell wall of bacteria causing their disintegration, attract phagocytes to the area of infection.

Table : Type of antibodies

ALLERGY

  • Allergy or hypersensitivity is the excessive immune response to common antigens. These antigens are present on / in certain substances called allergens (e.g., dust, pollen, moulds, certain foods, some medicines)
  • Allergy involves mainly IgE antibodies and histamine
  • Antihistamine is a medicine that gives relief from allergy. 
  • Types of hypersensitive reactions are - 
    • Type I reaction (immediate hypersensitivity reactions) involve IgE mediated release of histamine and other mediators from mast cells and basophils.
    • Type II reactions (cytotoxic hypersensitive reaction) involve IgG or IgM antibodies bound to cell surface antigens with subsequent complement fixation.
    • Type III reactions (immune complex reaction) involve circulating antigen antibody immune complexes that deposit in postcapillary venules with subsequent complement fixation.
    • Type IV reaction (delayed hypersensitive reactions or cell mediated immunity) are mediated by T cells rather than by antibody.

VACCINATION AND IMMUNISATION

  • Vaccine is the suspension of inactivated pathogens or antigenic protein of pathogen which is taken orally or injected to provide immunity for that pathogen.
  • Principle of vaccination is based on memory of the immune system. When an antigenic material is injected in a healthy person, it generates antibodies and memory cells as a primary immune response. When this active pathogen enters second time inside this body of vaccinated person, memory cells rapidly recognise and respond with massive production of lymphocytes and antibodies. So it destroys pathogens rapidly and the disease does not appear. Person becomes resistant for that disease after vaccination.
  • Types of vaccines
    • First generation vaccines: These vaccines are prepared by inactivating the whole pathogen but they have side effects, e.g., Oral polio vaccine (OPV), DPT.
    • Second generation vaccines : Antigenic polypeptides of pathogens are produced with recombinant DNA technology in transgenic organisms.
These are made by multiplication of surface antigen by genetic engineering. They have no side effects. E.g., Hepatitis B vaccine produced from transgenic yeast.
    • Third generation vaccine : These are highly potent, synthetic in nature & prepared by genes. They are also called DNA vaccine.
  • Passive immunisation may be induced by administration of an antibody containing preparation, transfer of maternal antibodies across the placenta and by transfer of lymphocytes to induce passive cellular immunity.
  • Passive immunisation may be natural or artificial.
  • Natural passive immunisation includes the passage of maternal IgG across the mammalian placenta. In humans, IgA is transmitted to the babys' gut via colostrum and milk.
  • Artificial passive immunisation is affected when immunodeficient patients are given doses of antibodies from a donor.

Table : Some Important Vaccines

NOTES
  • Edward Jenner (1796) noticed that milkmaids did not suffer from smallpox but they had scabs of cowpox. He transported the material from the sore of milkmaid who was suffering from cowpox to the young body of 8 year old. After sometime, he injected live smallpox material into that boy. But symptoms of diseases did not appear. He tried this procedure on other person and got success. He gave the term vaccination for this process.
  • Louis Pasteur: He discovered the process of inactivating the pathogen & prepared vaccines for anthrax, cholera, rabies.
  • Von Behring : He discovered the process of passive immunization and prepared the antidiphtherial serum by injecting diphtheria antigen into sheep. 
Von Behring is known as 'Father of passive immunization'.

CANCER

  • Cancer is an abnormal and uncontrolled division of cells, known as cancer cells, that invade and destroy the surrounding tissues. 
  • Generally cancer is defined as uncontrolled proliferation of cells without any differentiation.
  • Cancer cells are different from normal cells in some aspects. They do not remain confined to one part of the body. 
  • Neoplasm (called tumor) is a new abnormal tissue which is capable of continued growth.
  • Tumors may be benign and malignant.
  • Benign tumor is a large localized mass of abnormal tissue enclosed in connective tissue which does not invade adjacent tissue.
  • Malignant tumor is not encapsulated and is capable of invading adjacent tissues and distant sites.
  • They penetrate and infiltrate into the adjoining tissues and dislocate their functions. Some of the cancer cells get detached from the main site of origin and travel by blood and lymph to sites distant from the original tumour and form fresh colonies, called metastasis or secondary growth.

SYMPTOMS OF CANCER

  • Thickening or lump in the breast or any other part of the body.
  • Changes in bowel or bladder habits.
  • Indigestion or difficulty in swallowing.
  • Unexplained changes in weight.

TYPES OF CANCER

  • Types of cancer are carcinoma, sarcoma, leukemia and lymphoma.
  • Carcinoma is a cancer of epithelial tissue and their derivatives like mucous membrane, skin, lungs, breast etc.
  • Sarcoma is a cancer of primitive mesodermal tissue like connective tissue, bone, muscle, lymph nodes etc.
  • Leukemia is a blood cancer. It involves increased WBC count of blood due to increased formation in the blood marrow resulting in decreased erythropoiesis and RBC count.
  • Bone marrow grafting is used for the treatment of leukemia.
  • Lymphomas affect the lymphatic system.

CAUSES OF CANCER

  • Chemical or physical agents that can cause cancer are known as carcinogen
Depending on their mode of action, carcinogens fall into the following main categories:
    • Agents that can cause alterations in the genetic material (DNA), resulting in oncogenic transformation.
    • Agents that promote the proliferation of cells, which have already undergone genetic alterations responsible for oncogenic transformation. These agents are called tumour promoter, e.g., some growth factors and hormones.
    • Cancer causing DNA and RNA viruses (tumour viruses) have been shown to be associated with oncogenic transformation. 
  • Transformation of a normal cell into a cancer cell, if the regulation is upset.

TREATMENT

  • Surgery : By removing the entire cancerous tissue and infected lymph nodes.
  • Radiation: Cobalt therapy (Co-60), X-rays radiations are given. These radiations destroy the rapidly dividing cells.
  • Chemotherapy : Anti-cancerous drugs (like : Vincristine (weed - Catharanthus roseus = Vinca rosea), Vinblastine (weed - Catharanthus roseus = Vinca rosea),  (Cyclophosphamide) inhibit the DNA synthesis in cell cycle of cancerous cell but this has side effects.
  • Most of the cancers are treated by combination therapy of surgery, radiation and anti-cancerous drug.

AIDS

  • AIDS (Acquired Immuno Deficiency Syndrome) is a chronic life  threatening disorder which damages the human body's immune system.
  • AIDS is caused by HIV (human immuno-deficiency virus) which belongs to retrovirus (group of RNA virus)
  • The HIV can only survive in body fluids like blood, semen, vaginal secretion etc.
  • HIV is transmitted through body fluids by-
    • Sexual contact (most common mode of transmission) (Probability < 1 %)
    • Blood contact (100%), 
    • By mother to child by placenta (33%), by mother milk
  • HIV is not transmitted through ordinary contact (hugging, dancing, talking, touching etc.) with someone who has HIV or AIDS; sweat, tears or saliva etc.
  • The major cell affected by HIV is the helper-T-lymphocyte.
  • The HIV virus multiplies and slowly begins to destroy the CD4 lymphocyte (T cells or helper T-cells)
  • AIDS was first recognised in Hatai (USA) in 1981 among a group of young homosexuals who were addicts of heroin and other narcotics.
Fig. : Replication of retrovirus
  • AIDS includes 3 phases-
    • Asymptomatic phase - Initially within 2-12 weeks, there is no antibody production so infectivity of patients or activeness of virus is maximum in this  period. This period is called the window period (No specific symptoms appear in this phase  so ELISA test is negative in window period.)
Low grade fever, body aches, sore throat.
    • AIDS related complex (A.R.C.) - 3 to 6 weeks
It is characterized by -
      • Diarrhoea
      • Weight loss (> 1 0%)
      • Cough
      • Generalised lymphadenopathy
      • Fever.
    • Full blown AIDS – In this, patient becomes fully immune deficient and  T-Iymphocytes or CD4 count is less than 200 × 106 / litre.

INVESTIGATION

  • Screening test is Enzyme Linked Immuno Sorbent Assay (E.L.I.S.A.) .
  • Confirmatory tests : Western blot test : Detects antibodies (proteins) in patient's serum.
  • ELISA is a technique which can detect and even quantitate extremely small amount of a protein, antibodies or antigens with the help of enzymes. The commonly used enzymes are peroxidases and alkaline phosphatase.
  • Western blot test is the culturing of blood and testing plasma for virus.
  • Viral load test measures the amount of virus in the blood which will help in determining the probable progression of the disease. 

TREATMENT

  • Drugs used are -
    • AZT (Azidothymidine) or Zidowdine
    • DDI (Dideoxyinosine)
    • Foscarnet
These drugs inhibit the enzyme of  HIV. 
  • Highly active antiretroviral therapy (HAART) is a combination of three or more antiretroviral agents (called triple therapy or HAART), which has been highly effective in reducing the number of HIV particles in the bloodstream and as a result increases the CD4 count.

DRUGS AND ALCOHOL ABUSE

  • Drug abuse is defined as self administration of a drug for non-medical reasons. Abused drug include anabolic steroids, analgesics and antibiotics.
  • Drugs are classified on the basis of their mode of action on brain into two categories-
    • Psychoactive or psychotropic drugs
    • Psychedelic or hallucinogenic drugs.
  • Psychoactive drugs are also called as mood altering or neurological drugs.
  • Psychedelic drugs produce psychological effects like illusions and hallucinations.
  • Four categories of psychoactive drugs are- sedative and tranquilizers, opiate narcotics, stimulants and hallucinogens.
  • Alcoholism is the consumption of or preoccupation with alcoholic beverages to the extent that this behaviour interferes with the alcoholics normal personal, family, social life.
  • Alcohol decreases the activity of CNS thereby, reducing anxiety, tensions and inhibitions.
  • Alcohol decreases the secretion of ADH from the posterior pituitary gland causing increased urine output.
  • In the liver, alcohol is converted into a more toxic substance acetaldehyde which is used for energy by the cells.
  • Liver synthesizes fat from the alcohol, the extra fat decreases the production of enzymes and structural proteins.
  • The accumulation of fats results in fatty liver syndrome, leading to cirrhosis (replacement of liver cells by fibrous tissue)
  • Alcohol addiction lowers blood sugar levels, adversely affecting the brain.
  • Tobacco is the dried leaves of the plant Nicotiana tabacum and N. rustica. 
  • Nicotine is the substance that causes addiction to tobacco.
  • Nicotine is highly poisonous, nicotine present in a cigarette is sufficient to kill a person if taken intravenously.
  • Nicotine - stimulates passage of nerve impulse, causes muscles to relax and causes increased heart rate.
  • Tobacco smoke contains carbon monoxide, polycyclic aromatic hydrocarbons and tar.
  • The main harmful effects of smoking are respiratory diseases and cardiovascular disease.
  • One of the common cancer attributed to cigarette smoking is lung cancer.
  • The withdrawal symptoms include irritability, anxiety, craving, sleep problems, headache and lethargy. It may continue for 4-6 weeks and craving may continue for many months.
  • Some of the important measures for the prevention and control of alcohol and drug abuse among adolescents are as follows-
    • Drug education and counselling program.
    • Looking for danger signs.
    • Avoid undue peer pressure.
    • Seeking help from parents and peers.
    • Seeking professional and medical help.
    • Enforcing stronger laws and penalties.

Table : Categories of Psychotropic Drugs, their Effects and Clinical uses.

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Best Coaching Institute in Delhi for IIT JEE, NEET, AIIMS, PMT - Clear IIT Medical: Human Health and Disease | Biology Notes for NEET/AIIMS/JIPMER
Human Health and Disease | Biology Notes for NEET/AIIMS/JIPMER
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