What are the basic steps of the hemostasis?
- Injury to cells
- neurohumoral constriction of blood vessel
- von Willebrand Factor VWF on ECM initiates cascade
- Tissue factor
- Thrombin then fibrin
- wound heals then remove
- t-PA tissue plasminogen activator and endothelian
How do endothelial cells maintain blood fluidity?
- Regulate vessel tone >> secrete endothelin >> a potent vasoconstrictor
- Prevent plt aggregation & promote vasodilation >> secrete prostacyclin, nitric oxide
- Synthesize and secrete membrane associated heparin-like molecules (heparan sulphate) and thrombomodulin
- Modulate fibrinolysis
- synthesize tissue plasminogen activator t-PA
- synthesis plasminogen activators inhibitors (PAIs)
How do anticoagulants work?
Prevent interaction with adhesive proteins like collagen, VWF, Tissue Factor
What is tissue factor?
- Membrane protein located in smooth muscle, fibroblasts, and macrophages
- is the trigger for initiation of coagulation
What are the prothrombotic properties of endothelial cells?
- Synthesis, storage, and release of vWF
- storage and relase of factor VIII
- Weibel-Palade bodies
- Synthesize tissue factor
What are the important parts of platelets?
The dense body and the alpha granule
What are the chemicals in the Dense Body of platelets?
ADP, ATP , serotonin, calcium
What are the chemicals in alpha granules of platelets?
VWF, Factor V, Platelet Factor 4 (PF4) , fibrinogen
What are the three As of coagulation?
- Adhesion: to subendothelium mediated by vWF (especially at high shear rate) at site of injury
- Activation: metabolic >> secretion, membrane shape change and surface GPIIb/IIIa alteration
- Aggregation: fibrinogen cross-links GPIIb/IIIa, surface phospholipid exposed (coagulation matrix), and mechanical contraction (actomyosin)
Explain the Concept of Anti-platelet Therapy.
Inhibition of inappropriate platelet activation can prevent stroke, may prevent ischemic heart disease, retard coronary artery re-stenosis after coronary angioplasty or stenting
What are anti-platelet drugs?
- Aspirin: irreversibly inhibits platelet cyclo-oxygenase-1 (COX-1)
- Non-steroidal anti-inflammatory agents (e.g. ibuprofen): reversibly inhibit COX-1
- Clopidogrel (Plavix): blocks ADP receptor
- Abciximab (Reopro) and tirofiban (Aggrastat): block GPIIb/IIIa
Aspirin vs NSAIDs… which reversibly vs irreversibly block COX-1?
- Aspirin >> irreversibly
- NSAIDS >> reversibly
Where are the sites of synthesis and storage of
von Willebrand factor?
(hint: there are two for each)
- Synthesized in Endothelial cell and stored in Weibel-Palade body
- synthesized in megakaryocyte/platelet and stored in the alpha-granule
Explain the constituitive and stimulated secretion of vWF.
- Constitutive:
- from endothelium into plasma,mean (100%) = 10 ug/mL
- normal range 40-240%
- Stimulated:
- from endothelium by thrombin, fibrin, histamine, and DDAVP
- from platelet alpha- granules upon activation
What are the functions of vWF (class)?
- Adhesion
- Conformational change on binding to sub-endothelial collagens, esp. at high shear rates leads to binding to platelet GPIb
- Aggregation
- Binds platelet GPIIb/IIIa
- FVIII binding
- Protects FVIII from proteolytic cleavage
- Brings FVIII to site of hemorrhage
- FVIII:vWF ≈ 50:1 molar ratio (FVIII: vWF monomer)
Explain platelet activation.
When the endothelium is damaged, the normally isolated, underlying collagen is exposed to circulating platelets, which bind directly to collagen with collagen-specific glycoprotein Ia/IIa surface receptors.
This adhesion is strengthened further by von Willebrand factor (vWF), which is released from the endothelium and from platelets
vWF forms additional links between the platelets’ glycoprotein Ib/IX/V and the collagen fibrils.
These adhesions also activate the platelets
What are the functions of vWF (wiki)
- Factor VIII is bound to vWF while inactive in circulation; factor VIII degrades rapidly when not bound to vWF. Factor VIII is released from vWF by the action of thrombin.
- vWF binds to collagen, e.g., when it is exposed in endothelial cells due to damage occurring to the blood vessel.
- vWF binds to platelet gpIb when it forms a complex with gpIX and gpV; this binding occurs under all circumstances, but is most efficient under high shear stress (i.e., rapid blood flow in narrow blood vessels, see below).
- vWF binds to other platelet receptors when they are activated, e.g., by thrombin (i.e., when coagulation has been stimulated).
What is Factor
I
II
III
IV
V
VII
VIII
IX
X
XI
XII
XIII
also know: prekallikrein and high molecular weight kininogen
I = fibrinogen
II = prothrombin
III = tissue factor or thromboplastin
IV = Ca++
V = proaccelerin
VII = proconvertin
VIII = antihemophilic A
IX = antihemophilic B
X = stuart factor
XI = plasma thromboplastin antecedent
XII = hageman factor
XIII = fibrin stablizing factor
fyi
What factors are enzymes?
What factors are cofactors?
What are miscellaneous factors?
What factors are enzymes?
Factor IIa
Factor VIIa
Factor IXa
Factor Xa
Factor XIa
Protein C
tPA
plasmin
What factors are cofactors?
Tissue factor
Factor V
Factor VIII
Protein S
What are miscellaneous factors?
Fibrinogen
Factor XIII
Alpha2-antiplasmin
PAI-1
Antithrombin
What factors are vitamin K dependent?
Factor 2
Factor 7
Factor 9
Factor 10
Thrombin is a master conductor
What is the function of Factor XIII?
In the coagulation cascade, factor XIIIa functions to stabilize the fibrin clot by crosslinking the Lysine and glutamine side chains of α- and γ-chains of fibrin to form homopolymers
What is the quaternary complex?
Enzyme
Co-factor
phospholipid surface
Ca ions
What are endogenous anti-coagulants?
mostly endothelial derived molecules (heparin-like)
or proteins (thrombomodulin, t-PA, PAI-1)
