4.1.4 primary defences against disease Flashcards
define inflammation
redness & swelling of tissue caused by infection
define mucous membrane
specialised epithelial tissue covered by mucous
define primary defences
prevent pathogens entering body
describe how the skin acts as a primary defence
- outer layer of skin called epidermis & consists of layers of cells (mostly keratinocytes)
- these cells produced by mitosis at base of epidermis which migrate to surface of skin
- as they migrate, they dry out & cytoplasm of cells replaced by keratin (protein) = keratinisation (takes ~30 days)
- when cells reach surface they’re dead (keratinised layer of dead cells)
describe how blood clotting & skin repair acts as a primary defence
blood clotting:
- lacerations/abrasions damage skin & open body to infection
- blood clotting involves calcium ions & at least 12 clotting factors
- most clotting factors released from platelets/damaged tissue = activates enzyme cascade
- fibrin formed which forms network = traps platelets forming a clot
skin repair:
- when clots formed, it dries out & forms scab
- shrinks as it dries which draws sides of cut together (temporary seal)
- skin below is repaired (fibrous collagen deposited under scab, stem cells in epidermis divide by mitosis forming new cells, these migrate to edges of cut forming new skin & new blood vessels grow to supply oxygen/nutrients to tissues)
- the new tissues contract to draw edges of cut together
- once new skin completed, scab is released
describe how mucous membranes acts as a primary defence
- airways, lungs & digestive system are protected by mucous membranes
- epithelial layer contains mucous-secreting cells (goblet cells)
- extra mucous-secreting glands under epithelium
- epithelium has ciliated cells (tiny hair-like organelles which move to waft mucus to top of trachea where it enters oesophagus & is swallowed)
- (airways) mucous lines passages & traps pathogens in the air
- (digestive system) most pathogens killed by acidity of stomach
describe how coughing & sneezing acts as a primary defence
- response to irritation potentially caused by presence of pathogens/toxin they release
- sudden expulsion of air carries microorganisms with it
describe how inflammation acts as a primary defence
- signs tissue is infected
- presence of pathogens in tissue detected by mast cells
- mast cells release cell signalling substance ‘histamine’
- histamine has range of effects on surrounding tissue to help combat infection
- main effect of histamine = cause vasodialation & makes capillary walls more permeable to white blood cells/some proteins
- allows blood plasma & phagocytic WBC to leave blood/enter tissue fluid = increased production of tissue fluid causing swelling (odoema)
- excess tissue fluid is drained into lymphatic system where lymphocytes are stored = leads to pathogens coming into contact with lymphocytes & initiating specific immune responses
other primary defences
- eyes protected by antibodies & enzymes in tear fluid
- ear canal lined with wax which traps pathogens
- female reproductive system protected by mucus plug in cervical & maintaining relatively acidic conditions in vagina
