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Various types of diseases causing microorganisms are ever present in our environment. We are exposed to all types the body and cause various types of diseases. Therefore we do need defense mechanism for our body. The blood circulating systems as well as the lymphatic system play a very important role in the body defense mechanism.

These pathogenic microorganisms enter the body through the mouth, the nose or through open wounds. Eating and drinking contaminated as well as open wound being exposed to the air are all sources by which the microorganisms gain entry onto our bodies. The body’s defense against the entry of pathogens and diseases can be divided into three lines of defense.

First Line of Defense

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Skin a) The skin is a hard keratinized (a protein) outer layer. It serves as an effective barrier to microorganisms b) The pH value of the skin is low (pH 3-5) thus making it acidic and unsuitable for most microorganisms c) Besides the presence of the enzyme lysozyme which destroys or kills pathogen in the sweat and sebum helps the skin to ward or harmful microorganisms d) The clotting mechanism plays an important role in preventing the pathogenic microorganisms from gaining entry into body through the wound in the skin.

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Mucous Membrane a) The mucous membrane as well as the cilia lining the trachea and bronchi prevents the entry of microorganisms via the respiratory tract b) Microorganisms, dust particles spores and the like get caught up in mucous secreted by numerous goblets cells and is carried by the beating cilia towards the glottis. Laughing, sneezing or vomiting aid in eliminating these foreign substances c) Besides these mechanisms, the hydrochloric acid in the stomach kill any bacteria that come into contact with the food.

Second Line of Defense

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Phagocytic White Blood Cells a) Phagocytosis a process carried out by neutrophils and monocytes involves the surrounding and engulfing of pathogens, like bacteria, by extending pseudopodia b) The bacteria are enclosed within a vesicle, (ingested) and digested by enzyme secreted by the lysosome c) The lysosome fuses with the vesicle and discharges the enzyme that digests the food. The bacteria and the end products are absorbed into the cytoplasm.

The Third Line Defense

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The Immune Response a) This line of defense acts specially and involves the lymphocytes. Immunity is the ability of the body to fight diseases caused by pathogens b) Foreign proteins found in bacteria and viruses stimulate the immune response from the lymphocytes. These foreign proteins are referred to as antigens. An antigen stimulates the production of a corresponding protein called an antibody.

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c) The antibody combines with the antigen, neutralizes the antigen or destroys them in various ways i) Certain antibodies cause the antigen/ microorganisms to clump together making them ineffective in their action. This is referred to as agglutination ii) some antibodies dissolve the outer membrane or coat of microorganisms causing them to disintegrate. This action is referred to as lysis iii) Opsonin is yet another type of antibody which adhere to the outer surface of the microorganisms which are then engulfed and ingested by phagocytes iv) Antitoxins neutralize the toxin released by pathogenic microorganisms.

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d) The antibody – antigen reaction is specific. The production of antibodies in response to antigen is referred to as the immune response. The lymphocytes are the white blood cells that produce the antibodies. They are manufactured in the lymph nodes e) Lymphocytes’ reaction to antigen involves the production of antibodies that are specific to the antigen.

Immunity and Immunization

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Antigens stimulate the production of antibodies. Diseases are caused by the presence of bacteria or viruses in the body. The symptoms may be due to the antigen or foreign proteins of the bacteria or the toxic chemicals produced by the bacteria. Recovery from the disease followed by immunity depends mainly on the production of antibodies in the blood. Antibodies are proteins released into the blood which destroy kills or rids the body of these disease causing microorganisms different ways.

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Immunity is the body’s ability to fight the disease caused by the pathogens. The presence of antibodies in a person’s blood confers him or her immunity against specific diseases. When a person recovers from the disease the antibodies may remain in the blood stream briefly. However, the ability to produce these antibodies in another invasion by the same bacteria or virus prevents him or her from contracting the same disease. The person is said to be immune to the disease.

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Immunity can be acquired naturally from birth or after recovering from a disease like measles or chicken pox. Immunity can be induced in a person by vaccination or inoculation. Vaccine is a suspension of dead bacteria or inactivated viruses. When these are injected into the blood of a person his or her body is stimulated to produce antibodies to fight these injected bacteria or viruses. This process of injecting vaccine into a person is referred to as immunization. This confers the said person with artificial immunity.

The Several of Immunity

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1) Active immunity is the kind of immunity where the body makes its own antibodies in response to an antigen (pathogenic microorganisms, bacteria or viruses a) Active natural immunity is the kind of immunity acquired by a person who has recovered from a disease. For example if a person contracts measles and recovers from it, his body would have actively produced antibodies specific to fight the measles antigen, in this case the measles virus. These antibodies may remain only for a short time but the ability to produce these antibodies by the body is greatly increased. Thus the person is protected from further invasion by the measles virus.

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b) Active artificial immunity can be acquired by injecting antigen (dead, inactive bacteria or viruses), the vaccine into the body. This will induce the production of the appropriate antibodies. If and when the particular microorganisms enter the body, these antibodies actively fight the disease causing microorganisms eliminating them. Immunization by vaccination has been able to protect the people from such disease as tetanus, diphtheria, poliomyelitis and others.

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2) Passive Immunity – is one where a person receives antibodies into his body from external sources and not by actively producing them in his body a) Passive natural immunity is one which all of us posses from birth. The antibodies move across the placenta from the mother to the foetus. This confers passive but natural immunity on the young be it humans or other mammals.

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b) Passive artificial immunity – this involves the injection of anti-serum containing specific antibodies to ward of a specific antibodies to ward of a specific disease into a recipient from another individual or an animal like the horse. The diphtheria antibodies are prepared by injecting toxin obtained from the diphtheria bacillus into a horse. The toxin is first made harmless before injecting into the horse. The horse responds by producing antibodies in large amounts. The horse serum is then injected into a person to enable him or her to acquire passive but artificial immunity against diphtheria. The same technique is used to protect an individual who is already suffering from tetanus by injecting serum containing antibodies to fight the tetanus bacteria.

The Effects of HIV on the Body’s Immune System

HIV refers to the Human Immunodeficiency Virus. This virus causes AIDS or the Acquire Immune Deficiency Syndrome. The HIV acts by paralyzing the human immune system to such an extent that the victim is unable to fight the bacteria, yeast and viral infection which a normal healthy person can easily overcome. The human immunodeficiency virus attacks and kills the crucial immune cells called T cells. These cells, the lymphocytes are disabled and killed during the course of infection. They play an important role in the immune response.

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A healthy uninfected person usually has 800 to 1200 T cells’ per cubic millimeter of blood. In the blood of an HIV infected person this number declines rapidly. If these cells fall below 200/ mm³ the victim will become prone to infections and cancers. This indicates that he has AIDS which is the end stage of HIV disease. AIDS victims very often suffer infection of the lungs, intestinal tract, brain, eyes, skin and other organs. They also suffer “extreme” weight loss, diarrhea, and skin cancer or sarcoma and lymphomas. Thus HIV causes death by killing the lymphocytes (CD + T cells), interfering, with their normal function and weakening a persons immune system.

Transmission of HIV

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The HIV virus can be transmitted from an infected person to a healthy person via the seminal fluid, vaginal fluid, blood as well as mother’s blood. Transmission of HIV can occur through the following ways: a) having sexual relationship with a HIV carrier b) sharing needles with HIV infected drug addicts c) during blood transmission between an HIV infected mother to her unborn child in the womb or via mother’s milk fed to her baby.

Prevention of AIDS

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Using of condoms during sexual relationship. Avoiding the sharing of needles with HIV infected drug users and practicing morally healthy lifestyle by not having multi sex partners, random sex with unknown persons, prostitutes or drug addicts who could be HIV carriers. Avoid sharing blades and tooth brushes as tainted shaving blades which could be a source of HIV infection.

Info Gallery

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Phagocytosis is the ingestion of cells, cells debris or large particles into a ‘food vacuole’ by a big engulfing cell called a phagocyte. They develop from white blood cells, known as monocytes, which have passed out of the bloodstream and into tissues.