(i) Non – specific defence mechanisms which try to prevent the entry of micro organisms.
(ii) Specific defence mechanisms are active processes which destroy the microorganisms once they manage to get in the body. It is also called as immune system.
1. Non – specific defence mechanisms
These mechanisms guard against the entry of micro-organisms in the body.
a. Skin: Skin forms the first line of defence. It forms the hard, keratinised outer layer of the body which covers all external parts and forms an effective barrier for most bacteria and viruses. The secretions of oil and sweat glands make the surface pH acidic (pH 3 to 5) which does not let microorganisms to survive for long. Certain friendly bacteria also release acids and other metabolic wastes which also inhibit the multiplication of pathogens. The salts and fatty acids present in perspiration contain lysozymes that destroy the bacterial cell walls. Tears secreted by tear glands also contain lysozymes which prevent the eye infection. Saliva also contains the lysozymes that kill the bacteria present in the foods and drinks. Any bacteria left are killed by the secretion of the stomach. The respiratory tract is lined by the mucous membrane. First the cilia and fine hair filter out the undesired particles in the nostrils and then mucus – the slimy substance traps the bacteria. In the trachea or bronchi, the movements of cilia sweep bacteria towards the throat from where they are expelled by coughing or sneezing.
b. Phagocytic cells or W.B.C.: Phagocytic cells form the second line of defence and work when the first line of defence is broken and bacteria do gain entry through abrasion or wound in the skin. At the place of injury, clotting not only prevents bleeding but also blocks the entry of bacteria. Dilation of small blood vessels at injury increases the blood flow. The increased permeability of capillaries lets phagocytes pass out into the intercellular spaces and engulf the invading bacteria. Phagocytosis is generally carried out by neutrophils. The pus formed at he infected wound is actually the debris of the battle i.e. dead cells, digeste
d bacteria and broken phagocytes in the blood serum. Inflammatory response: At times the phagocytosis results in a hot red, swollen inflamed area at the site of infection. Redness is due to increases flow of blood. The lymph helps by carrying bacteria and phagocytes that have engulfed bacteria to the lymph nodes where they are filtered out. The inflammatory response is due to a chemical histamine released by the lymphocytes, and the damaged tissues which causes dilation of the blood capillaries. These reactions are generally localized i.e. confined around the wound. Many a time the fight between microorganisms and W.B.C. results in rising of temperature. Such an inflammatory response is wide spread and is called a systemic reaction. High fever not only inhibits the growth of germs but also activates the body defenses and is actually beneficial if not too high and uncomfortable. The fever is caused by either the toxins released by the pathogens or by the chemicals called pyrogens (the fever producing substances) released by W.B.C. that set the body's thermostat at a higher temperature.
2. Specific defence mechanism
The first and the second line of defence were nonspecific as they acted on any type of bacteria but this third line of defence by antibodies is very specific. An antibody act against a specific bacteria or antigen only. An antigen is any foreign protein or a polysaccharide that is not found in the organism's body. Viruses, bacteria or their toxins and the cells of other person, all contain proteins not recognised in the body and hence act as antigens. An antigen stimulates the body to produce a specific antibody. The word antigen is a shorten form of antibody generating. The antibodies interact with the antigen and either destroy them or make them inactive. The antibodies are globular proteins and are called as immunoglobulins (or Ig in short form). They are produced in the lymph nodes, spleen and by the thymus gland. Entry of an antigen in the form bacteria or virus triggers a reaction in the body as a result of which the antibodies produced defend the body in various ways and try to neutralise the antigens. Antigens are not only parts of microorganisms but certain blood cells, pollen, eggs white, fruits or vegetables may also act as antigens and stimulate the immune system of the body.
(ii) Specific defence mechanisms are active processes which destroy the microorganisms once they manage to get in the body. It is also called as immune system.
1. Non – specific defence mechanisms
These mechanisms guard against the entry of micro-organisms in the body.
a. Skin: Skin forms the first line of defence. It forms the hard, keratinised outer layer of the body which covers all external parts and forms an effective barrier for most bacteria and viruses. The secretions of oil and sweat glands make the surface pH acidic (pH 3 to 5) which does not let microorganisms to survive for long. Certain friendly bacteria also release acids and other metabolic wastes which also inhibit the multiplication of pathogens. The salts and fatty acids present in perspiration contain lysozymes that destroy the bacterial cell walls. Tears secreted by tear glands also contain lysozymes which prevent the eye infection. Saliva also contains the lysozymes that kill the bacteria present in the foods and drinks. Any bacteria left are killed by the secretion of the stomach. The respiratory tract is lined by the mucous membrane. First the cilia and fine hair filter out the undesired particles in the nostrils and then mucus – the slimy substance traps the bacteria. In the trachea or bronchi, the movements of cilia sweep bacteria towards the throat from where they are expelled by coughing or sneezing.
b. Phagocytic cells or W.B.C.: Phagocytic cells form the second line of defence and work when the first line of defence is broken and bacteria do gain entry through abrasion or wound in the skin. At the place of injury, clotting not only prevents bleeding but also blocks the entry of bacteria. Dilation of small blood vessels at injury increases the blood flow. The increased permeability of capillaries lets phagocytes pass out into the intercellular spaces and engulf the invading bacteria. Phagocytosis is generally carried out by neutrophils. The pus formed at he infected wound is actually the debris of the battle i.e. dead cells, digeste
d bacteria and broken phagocytes in the blood serum. Inflammatory response: At times the phagocytosis results in a hot red, swollen inflamed area at the site of infection. Redness is due to increases flow of blood. The lymph helps by carrying bacteria and phagocytes that have engulfed bacteria to the lymph nodes where they are filtered out. The inflammatory response is due to a chemical histamine released by the lymphocytes, and the damaged tissues which causes dilation of the blood capillaries. These reactions are generally localized i.e. confined around the wound. Many a time the fight between microorganisms and W.B.C. results in rising of temperature. Such an inflammatory response is wide spread and is called a systemic reaction. High fever not only inhibits the growth of germs but also activates the body defenses and is actually beneficial if not too high and uncomfortable. The fever is caused by either the toxins released by the pathogens or by the chemicals called pyrogens (the fever producing substances) released by W.B.C. that set the body's thermostat at a higher temperature.2. Specific defence mechanism
The first and the second line of defence were nonspecific as they acted on any type of bacteria but this third line of defence by antibodies is very specific. An antibody act against a specific bacteria or antigen only. An antigen is any foreign protein or a polysaccharide that is not found in the organism's body. Viruses, bacteria or their toxins and the cells of other person, all contain proteins not recognised in the body and hence act as antigens. An antigen stimulates the body to produce a specific antibody. The word antigen is a shorten form of antibody generating. The antibodies interact with the antigen and either destroy them or make them inactive. The antibodies are globular proteins and are called as immunoglobulins (or Ig in short form). They are produced in the lymph nodes, spleen and by the thymus gland. Entry of an antigen in the form bacteria or virus triggers a reaction in the body as a result of which the antibodies produced defend the body in various ways and try to neutralise the antigens. Antigens are not only parts of microorganisms but certain blood cells, pollen, eggs white, fruits or vegetables may also act as antigens and stimulate the immune system of the body.
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