F5 1.5 body s defence mechanism

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F5 1.5 body s defence mechanism

  1. 1. Body’s Defence Mechanism You must be able to : Identify the 3 lines of defence mechanism Describe phagocytosis State the meaning of antigen & antibody State the meaning of immunity & imunisation Relate antigen & antibody to imunity Name & give examples of various types of immunity
  2. 2. Body’s Defence Mechanism 1st Line of Defence 3rd Line of Defence 2nd Line of Defence
  3. 3. 1stentering Defence by mean of physical & Prevention of pathogens Line of the body chemical barriers A non-specific defence, that is never differentiate among various type of pathogens. This includes: i) Skin As a physical barrier, skin is made up of a dead keratinised layer, tough enough for pathogens to penetrate If there is a scratch or cut, the blood clots to seal the wound & avoids infection Also acts as chemical barrier as it secretes sweat which contains salt. Sebaceous glands produce sebum which contains acid & oil. All these substances are unfavourable for growth of microorganisms Sweat also contains lysozyme which destroys pathogens ii) Tears & Saliva Contain lysozymes which protect the eyes & mouth from pathogen invasion.
  4. 4. 1st Line of Defence iii) Gastric juice in stomach Contain hydrochloric acid which destroys most pathogens in foods & drinks taken. iv) Mucous membranes Secrete mucus in nasal cavity & trachea to trap the dust particles & spores The cilia in the respiratory track sweep the trapped particles to the pharynx & stimulates sneeze @ cough to expel out the pathogens.
  5. 5. The killing action brought by some of the white blood cells like neutrophil & monocyte (Phagocytes). The process is called phagocytosis. Phagocytosis occur when pathogens get through the first line of defence. Phagocytes move to the infected area due to the stimulation by chemicals released by damaged cells, example cut skin. Sometimes the phagocytes are killed by toxins produced by the pathogens. Dead bacteria, tissue cells & phagocytes may accumulate to form pus at the site of injury. 2nd Line of Defence Phagocytosis
  6. 6. 3rd Line of Defence

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