Immunity is the body’s self-defense mechanism againstdiseases. Pollutants and germs can enter the human body through skin, mucusmembranes (eyes, nose, urinary or genital tracts), food and water, as well asthe air that we breathe. The Human Defense system works at two levels. That islocal defense mechanism, which is prevention of entry of germs. And the immunesystem.
The primary local defense system tries to form mechanical barriers,thus preventing the entry of germs. The Immune system fights the germs afterthey have entered into the body tissues. The main benefits of the local defense system are its quickresponse and power to fight against a wide range of potentially infectiousthreats.
The parts of the local defense system are independent of previousexposure to infections. The local Defense system consist of: Protectivemechanical barriers; germs or foreign bodies thrown out if entered; germkilling secretions; germ fighting white blood cells.Skin, hair and mucus form primary mechanical barriers of ahuman body. Skin is made of the protein keratin, it forms a protective coveringon the body and is impermeable to germs. Any cut or injury on the skin opensthe way for germs to invade the body.
Mucus is the slimy section of theepithelial cells that forms a delicate covering of many organs. The mucouspresent inside the windpipe and the nasal chamber traps the germs. Even ifgerms enter the respiratory or the digestive systems, they are thrown out byvomiting, coughing and sneezing. Sometimes lose motions of diarrhea also helpto clear the digestive tract of the germs.
Saliva, sweat tears and nasal secretions contained severalgerms killing secretions. The hydrochloric acid secreted by the stomach, kills thegerms that enter our body through the food. The white blood cells or phagocytes are the cells of theimmune system. They fight with the foreign materials and prevent the body frominfections.
The white blood cells squeeze out the blood capillaries by theprocess of “diapedesis” and destroy the germs. This process is known asphagocytosis.The local defense system may not be effective at all times,in certain cases the microbes invade all the mechanical barriers and enter thedeeper tissues and organ systems. Under such circumstances the human body producesspecial proteins: antibodies and antitoxins to fight against the threat.
Inother words, “Immunity” is defined as the capacity of our body to deal withforeign substances as bacteria, viruses, toxins, etc. that enter our body andthe render them harmless. Immunity can be innate or acquired. Innate immunity(also called natural or innate immunity) is by virtue of the geneticconstitutional make-up of the body. It is there in the body without anyexternal simulation or previous infection.
Innate immunity can be specific andnonspecific. Specific immunity is the natural resistance against a specificgerm only. For example human beings are immune to a highly infectious diseaseof dogs known as distemper, which kills about 50% of all infested dogs. Non-specificimmunity is natural resistance to all kind of infections in general. Forexample: human beings are immune to highly infectious diseases of plants.Acquired Immunity is the resistance which an individual acquires during his orher life-time.
This immunity is of two types, namely actively acquired immunityand passively acquired immunity. Actively acquired immunity is the resistancedeveloped due to a previous infection or due to an antigen. Antigen is thechemical found on the surface of the disease-causing germ cell. If the antigenis introduced in the body by artificial means during vaccination, it can leadto an artificially acquired active immunity. On the other hand if the antigenenters his body naturally, it is called naturally acquired active immunity.
This kind of resistance is possible due to some previous infection or entranceof antigen into our body naturally. In either of the cases the body’slymphocytes react by producing antibodies or killer cells. The producedantibodies circulate in the blood and the lymph, thereby killing the microbes.Passively acquired immunity is the introduction of ready-made antibodies froman outside source. It is of two types. Naturally acquired passive immunity: in this type of defensemechanism, the prepared antibodies of the mother, enters the foetus through theplacenta.