primary defences Flashcards
(8 cards)
what is a primary defence
barrier t pathogens preventing their entry
what does the skin do as a primary defence
-outer layer is called epidermis, consists of many layers of cells
-most of these cells are keratinocytes
-produced by mitosis at the base of epidermis
-they then migrate to the surface of the skin
-as they migrate then dry out and the cytoplasm is replaced by keratin
-this is keratinisation. it takes 30 days
-by the time the cells reach the surface they are no longer alive
-keratinised layer of dead cells acts as a barrier to barrier to pathogens
how does blood clotting and skin repair act as a primary defence
-abrasions in skin open body up to infection
-blood clot forms
-temporary seal to prevent infection and repairs skin
-blood clots must not be formed in blood vessels
-blood clotting involves Ca2+ ions and 12 clotting factors
-clotting factors are released from platelets and from damaged tissues
-these factors activate an enzyme cascade
-once the clot forms it dries out and forms a scab
-scab shrinks pulling skin together
-seal forms and skin forms under
-fibrous collagen is deposited under the scab
-stem cells in the epidermis then divide by mitosis to form new cells which migrate to the edges of the gut and differentiate to form new skin
-new blood vessels grow to supply oxygen to new tissues
-tissues contract to draw the edges of the cut together so repair is completed
-as new skin is completed the scab will be released
how does mucous membranes act as primary defence
-goblet cells secrete mucus
-mucus traps pathogens
-cilia on ciliates epithelial cells wafts mucus towards back of throat
-enters oesophagus
-swallowed and passes down digestive system
-most pathogens killed by acidity of stomach
-this denatures the pathogens enzymes
how does inflammation act as a primary defence
-inflammation is a sign of infection
-tissue may feel hot and painful
-presence of microorganisms in a tissue is detected by specialised cells called mast cells
-these release a signalling molecule called histamine
-histamine acts to fight infection
-causes vasodilation
-makes capillary walks more permeable to WBCs and sone proteins
-blood plasma and phagocytic WBCs leave the capillary and enter tissue fluid
-leads to increased tissue fluid which causes swelling (oedema)
-excess tissue fluid drains into lymphatic system
how does eyes act as primary defence
protected by antibodies and enzymes in tear fluid
how do ears act as primary defences
canal lined by wax which traps pathogens
how does inflammation act as a primary defence
-inflammation is a sign of infection
-tissue may feel hot and painful
-presence of microorganisms in a tissue is detected by specialised cells called mast cells
-these release a signalling molecule called histamine
-histamine acts to fight infection
-causes vasodilation
-makes capillary walks more permeable to WBCs and sone proteins
-blood plasma and phagocytic WBCs leave the capillary and enter tissue fluid
