→ 3 lines of defence mechanism
• the first line of defence :
Physical and chemical barriers that prevent the pathogens from entering the body.
(pathogens : disease-causing microorganism, e.g : bacteria, viruses, parasites)
• e.g
The skin mucous membrane others
• rough outer layer • line the trachea, • tears and saliva
• impenetrable respiratory passage ways, (lysozyme), protect
• secretes sebum ( acid & oils digestive & urinary tracts, eyes & mouth
prevent bacteria growth) stop entry of microorganism • HCl acid (stomach)
• the sweat (lysozyme), breakg • secretes mucus (lysozyme) destroy pathogen
down cell walls of certain bact. traps & destroys bact. entry via food @
drink consumed.
* specific
• the second line of defence
Phagocytic white blood cells (phagocytes) perform phagocytosis..
• engulf and ingest m/o or other foreign particles such as cellular debris.
• neutrophils & monocytes.
• they enter the interstitial fluid by squeezg through capillaries wall develop into macro-
phages
• when a phagocyte encounters the pathogen it engulf & destroyed by lysozyme in the
phagocyte.
* non-specific
• the third line of defence
• involves in immune system. ( Immunity : the body resistance to the pathogen which
causes a specific disease).
• specific / targeted defence
• antigens :specific molecule (protein) at the external surface of an invading m/o. Immune
system recognizes as foreign. E.g bacterial toxins, snake venom. When immune system
identifies the antigen, antigen induce the lymphocytes to release antibody in the blood
stream to destroy antigen.
• antibody :protein found on the surface of lymphocytes or protein released by lymphocy-
tes into the blood plasma. Each antibody can only bind to a specific antigen.
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