coagulation and the clotting cascade Flashcards
physiological response to cut
- activating factors release from tissue and platelets
- clotting factors activated in plasma
what are clotting factors
plasma proteins
where are clotting factors mostly produced
in the liver
what does lack of clotting factor mean
haemophilia A
(VII deficiency)
haemophilia B
(IX deficiency)
characteristics of platelets
very small
essential for clotting of damaged vasculature
what regulates platelet production
thrombopoietin
life span of platelets
approx 7-10 days
do platelets stick to tissues
yes, not to be confused with clotting
formation of plateletss
haemocytoblast to
myeloid stem cell to
megakaryoblast to
promegakaryocyte to
megakaryocyte to
platelets
what is haemostasis
stoppage of blood flow after damage
steps of haemostasis
- vascular spasms (vasoconstriction at injury)
- platelet plug formation (plugging the hole)
- coagulation (blood clotting)
- fibrin clot formation
what does vascular endothelium do
inhibit blood clotting
makes prostacyclin and NO, both inhibit platelet aggregation
is the vascular endothelium conductive to clot formation
no
it displays membrane proteins that inhibit clotting (heparin like molecules )
what does the vascular endothelium store
von willebrand factor granules
constitutively expressed and secreted into circulation or sub-endothelium
first response to vascular injury
vasoconstriction is stimulated
- compression of vessel by escaping blood
- injury chemicals released by injured cells
- reflexes from adjacent pain receptors
formation of a platelet plug step 1
platelets attach to damaged vessel wall to plug it
formation of a platelet plug step 2
platelets produce thromboxane A2
formation of a platelet plug step 3
serotonin/histamine release enhances vascular contraction
formation of a platelet plug step 4
ADP - attracts and stimulates platelets at site
formation of a platelet plug step 5
prostacyclin - inhibits aggregation at other sites
does a sharply cut vessel bleed longer or shorter than a tore vessel
a sharply cut vessel undergoes less spasm
so bleeds longer, than a tore vessel
what are the coagulation clotting pathways
- intrinsic - all components are in the blood
- extrinsic - at least one component from tissue, injury response
what is needed for activation of VIIa
tissue factor
when do TF and VIIa contact
only after injury
what does TF-factor VIIa complex activate
factor XIa
coagulation clotting step 1
platelet cells activated by damage
coagulation clotting step 2
PF3 and/or tissue factor produced by platelet cells
coagulation clotting step 3
factor X activated
coagulation clotting step 4
prothrombin activator (enzyme) produced
coagulation clotting step 5
prothrombin activator (enzyme) produced
coagulation clotting step 6
prothrombin conversion to thrombin
coagulation clotting step 7
thrombin stimulates fibrinogen to fibrin mesh
what are the two roles of thrombin
conversion of fibrinogen to fibrin
platelet adhesion (activation)
factors limiting normal clot growth
- blood moves too fast to allow pro-coagulants
- factors interfere with normal clotting
- antithrombin III deactivates thrombin
- proteins C and S inhibits clotting
- heparin inhibits thrombin, prevents adherence of platelets
what is the clotting screen
a bundled group of tests used pre-operatively to asses bleeding conditions and some therapies
what do routing clotting tests comprise of
the prothrombin time (PT)
fibrinogen
activated partial thromboplastin time
thrombin time
D-dimer (broke down clot)
how to work out iNR
patient PT / Control PT
what does prothrombin time measure
activation of factor X by extrinsic pathway
