3-Hemostasis Flashcards
1- Objective of lesson
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1- Definition of hemostasis 2- Haemostatic components 3- Concepts of normal hemostasis 4- Primary and seccondary hemostasis 5- Role of coagulation in hemostasis 6- Fibronolytic system
2- Defintion of Hemostasis
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Hemostasis is the stoppage of bleeding, which is vitally important when the blood vessels are damaged.
Following an injury to blood vessels several actions may help prevent blood loss, including:
1- Vascular spasm
2- Platelet plug formation
3- Blood clotting
3- Concepts of hemostasis
1- It is a tightly regulated process that maintainn blood in a fluid state in normal vessels
2- Permit the rapid formation of a hemostatic clot at the site of a vascular injury ( to limit blood loss)
3- Can cause Thrombosis:
- a pathological counterpart of hemostasis
- blood clot (thrombus) formation within intact vessels
4- Both hemostasis and thrombosis involve;
- Vascular wall
- platelets
- Coagulation cascade
4- Concepts of normal hemostasis
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Under normal conditions, the formation and dissolution of thrombi is maintained in a delicate balance.
1-Without this balance, the individual may experience either excessive bleeding (poor clot formation).
2-Vaso-occlusion (uncontrolled formation of thrombi in vascular system, occluding vessels and depriving organs of blood).
The endothelium in regulating Thrombosis
Antithrombotic factors
(5)
1- Inhibition of platelet aggregation
- PGI2
- Echo-ADPase
- EDRNF (NO)
2- Inhibtion of coagulation:
- Thrombomudoulin
- Heparin
- A2 macroglobulin
3- Fibrinolysis
- Tissue plasminogen
- Urokinase
The endothelium in regulating Thrombosis
Thrombotic factors
(5)
1- Platelet aggregation and adhesion:
- Platelet activating factor
- vWF factor
2- Coagulation:
- Tissue factor
- Factor V
- Binding IXa, Xa
3- Inhibtion of fibrinolysis
- tPA inhibitor
Explain the primary and secondary injury of hemostasis
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Hemostasis can be divided into two stages:
Primary and Secondary.
Primary hemostasis includes the platelet and vascular response to vessel injury.
Secondary hemostasis includes the coagulation factors response to such injury.
Together, platelets, vessels, and coagulation factors combine to stop bleeding and allow for vessel repair through formation of a stable fibrin-platelet plug at the site of injury.
State the 5 steps of hemostasis
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1- Vasoconstriction
2- Primary hemostasis ( platelet plug formation)
3- Secondary hemostasis (FIbrin Clot formation)
4- Clot retraction
5- Clot dissolution
Role of vasoconstriction
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1- Caused by trauma 2- Release of Endothelin 3- Bind to endothelin receptors 4- Induces the elevation of intracellular Ca2+ 5- Causing the vasoconstriction reflex
Role of Primary Hemostasis: Platelets
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Platelets bind to exposed extracellular matrix and are activated, undergoing a shape change and granule release; primary hemostatic plug.
1- Platelet adhesion 2- Shape change 3- Granule release 4- Recruitment 5- Aggregation (hemostatic plug)
What are platelets ?
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They are disc shpaed, anucleate cell fragments.
Megakaryocytes shed platelets in the bone marrow.
Functions:
a. form the hemostatic plug
b. provide a surface taht recuits and concentrated activated coagulation factors
Types of cytoplsmic granules
- A-granules:
- P-selectin,
- fibrinogen,
- fibronectin, -
- factors V and VII
- platelet factor 4 (a heparin-bindnig chemokine)
- platelet derived growth factor (PDGF)
- Transorming groth factor-B (TGF-B) - Dense (or d) granules:
- ADP and ATP
- ionized calcium
- histamine
- Serotonin
- epinephrine
What are the receptors present on platelet membranes?
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1- GPCRs:
- ADP receptor
- thrombin
- epinefrin
- TXA2
2- Integrins:
- Glycoproteins iib/iiia: binds fribirnogen
- Glycoprotein ib: binds vWF
- Glycoproteins VI and Ia
- Collagen Ig-like recepetors
3 - Selectins
- P-Selectin
