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BIOL 201 (86)

Defense System

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Queen's University
BIOL 201
Elaine Power

Defense System  Skin is composed of dead cells containing the indigestible protein keratin  Sebum produced by the skin lowers the pH to inhibit growth of pathogens  Lysozymes in salvia, sweat and tears are anti-bacterial enzymes  Many ingested bacteria in the stomach are destroyed by acid (HCl)  A sticky substance, mucus, traps pathogens in the respiratory tract  Cilia moves away mucus towards the throat to protect gas exchange surfaces  The immune system targets foreign materials and pathogens Inflammatory response  Histamine is released into the wound by white cells  This increases vasodilation and increases vascular permeability  Vasodilation increases the local blood flow → area becomes red, warm  Increased permeability allows escape of tissue fluid into the tissues  Tissue fluid contains plasma proteins (antibodies) and may cause swelling Phagocytosis  White cells (phagocytes) contain digestive enzymes within lysosomes o Neutrophils primarily engulf bacteria o Macrophages engulf larger particles; including old and infected red blood cells  Found in blood, lymph systems and tissues  Squeeze through gaps in the walls of venules to enter tissues  This allows them to move faster to tissues infected with pathogens  Phagocytes are attracted by c
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