AS/A level Biology Summary - non-specific & specific defences against pathogens

NON-SPECIFIC DEFENCES (primary)

BLood clo:ng + wound repair
When a person cut themselves, blood flows out —> so blood clo8ng happens to
prevent pathogens from entering

⁃ Platelets rush to collagen in damaged area and adhere —> forming a temporary
clot TEMPORARY PLATELET PLUG
⁃ And secrete 1. ThromboplasBn 2. Serotonin

ThromboplasBn (clo8ng factor) ; serotonin: makes SMOOTH MUSCLES IN WALLS OF
blood vessels contract —> reduce blood flow to damaged area

⁃ ThromboplasBn, along with Ca2+, converts prothrombin to thrombin (which is an
enzyme that is now acBvated)
⁃ Thrombin converts fibrinogen to fibrin (then forms FIBRES)
⁃ Then aSaches to platelets to form a net trapping RBC and platelets —>
(permanent) CLOT formed


Clot then turns into a scab, the process is:
⁃ Fibrous collagen deposits UNDER SCAB
⁃ stem cells DIVIDE BY MITOSIS, move to the edge of cut, differenBate to form new
cells FORM NEW SKIN
⁃ New blood vessels GROW to SUPPLY NUTRIENTS and oxygen to new cells
⁃ TISSUES CONTRACT TO DRAW EDGES OF CUT TGT —> REPAIR COMPLETE
⁃ Scab is the released