Flashcards in Dixon cardiovascular system Deck (26):
what are the main components of blood
what does plasma contain
proteins (albumins, immunoglobulins, fibrinogen and clotting factors)
5-9 day lifespan
used in haemostasis, blood vessel repair, inflammation
red bi-concaved disc
120 days lifespan
variable life span
important for defence
what is haemostasis?
what are the three mechanisms
arrest of blood flow from damaged vessel.
vascular spasm, coagulation cascade
platelet activation and plug formation
describe vascular spasm
damage to vessel wall
vasoconstriction of vessel wall
decrease in blood flow through damaged vessel.
role of coagulation in haemostasis
solidifcation of blood (clot formation) through amplifying cascade.
soluble fibrinogen is converted to insoluble fibrin by thrombin. the fibrin forms a mesh which traps blood cells and platelets.
what are the differences between the extrinsic and intrinsic part of the coagulation cascade?
needs extravascular tissue factor
activated after tissue trauma
in vivo mechanisms
very fast (seconds)
all components are available in blood
in vivo AND in vitro
what factors are involved in the intrinsic pathway/contact pathway?
factor 2 is cleaved to factor 2a.
factor6 is cleaved by factor2a into factor6a
factor 9 is cleaved by factor 6a into factor 9a.
factor 9a, with factor 8a/ca2+ is used in the extrinsic pathway
what factors are used in the extrinsic pathway?
factor7 is cleaved by tissue factor into factor7a
factor 10 is cleaved by factor 9a/ca2+/factor8a into factor 10a.
prothrombin (factor2) is cleaved by factor 10a/ca2+/5a into thrombin (factor 2a)
what are the coagulation factors? (generic overview)
present in blood as inactive precursors
formation of precursors require reduced form of vitamin K.
theyre activated by proteolysis (factor 2 to factor 2a)
they are proteolytic enzymes when activated
amplification is built into the cascade
what is the role of thrombin in haemostasis?
converts fibrinogen into fibrin
factor13 is cleaved by thrombin into factor13a which causes fibrin monomers to form stronger bonds with eachother
induces platelet aggregation and gp2b/3a expression
inhibited by antithrombin 3 and fibrin
how does the body prevent uncontrolled coagulation and removal of clots?
coagulation checkpoints and fibrinolysis
what are the coagulation checkpoints?
1) fibrin inhibits thrombin
2) protein C from plasma is activated by thrombin and proteolytically inhibits factor 5a and 8a
3)antithrombin3 from plasma inhibits thrombin and other factors
4) heparin from endothelium , mast cells and basophils are a cofactor for at3
what is the purpose of fibrinolysis
activated simultaneously with coagulation cascade.
what is the process of fibrinolysis
a clot is formed that contains inactive plasminogen
plasminogen activators convert plasminogen to plasmin (digests fibrin, factor 2, 5 and 8)
protein c inhibits factors 2, 5 and 8 while the clot dissolves
what is platelet plug formation
process that is integrated with coagulation pathway in which platelets go through three stages to form a clot
what are the three stages of platelets plug formation?
discuss platelet adhesion
when blood vessel wall is damaged platelets will undergo adhesion to collagen.
the platelet surface have adhesive receptors which interact with the collagen directly or indirectly.
discuss platelet activation
platelets are activated and will change shape from round to spikey?
they release granules of mediators which promote the clotting cascade, platelet activation and aggregation, wound repair, and inflammation.
thromboxane A2 (txa2) is released and causes the activation and activation of more platelets.
discuss platelets aggregation
glycoprotein 2b/3a receptors bond with fibrinogen which bonds with more platelet receptors and forms bonds and eventually a clot.
how is thromboxane synthesised?
membrane phospholipids are cleaved by phospholipase A2 into arachidonic acid and lyso-PAF (converted to PAF)
cyclo-oxygenase (COX) induces arachidonic acid to be converted to cyclic endoperoxides
cyclic endoperoxides is cleaved by thromboxane synthase into TXA2.
TXA2 acts as a vasoconstrictor and promotes platelet aggregation.
OR// cyclic endoperoxides is cleaved by prostacyclin synthase into prostacyclin.
prostacyclin is a vasodilator and inhibits platelets aggregation.
what is the function of GP2B/3A receptors?
1) binds fibrinogen, von Willebrand's factor and other proteins
2)expressed only on activated platelets
3) final common pathway in stimulation for platelet aggregation
4) functional antagonists are used as drugs e.g. tirofiban
how is the coagulation cascade integrated with the platelet process?
platelets are activated by thrombin
activated platelets provide surface for coagulation cascade to occur