Lecture 20: Hemostasis Flashcards
4 steps of hemostasis?
1) Vascular spasm
2) Formation of a platelet plug
3) Formation of a blood clot
4) Repair of damage
What is hemostasis?
Steps taken by the body to limit blood loss
*Not confined only to the production of a blood clot!
Primary cause of vascular spasm?
Myogenic response to injury, no neurons or reflexes involved
Platelets release what that contributes to the vascular spasm?
Platelet factors
- Serotonin
- Thromboxane A2
*Both vasoconstrictors
What is a small component/contributor to vascular spasm, but is not necessary?
Neural reflex initiated by mechanical injury and pain
Purpose of vascular spasm?
Reduce blood loss by slowing/stopping blood flow out
Damage to vessel wall exposes?
Collagen
What will bind to exposed collagen?
Platelets
Step I of formation of platelet plug involves, its function?
Von Willebrand Factor (plasma protein) serves as anchor binding collagen and platelet (receptor)
What occurs during step II of formation of platelet plug?
Binding of platelet receptor (integrin) to collagen
What 2 things occur during activation of platelet bound to its receptor which has bound collagen?
1) Platelets swell
2) Extend podocytes
After the platelet swells what occurs?
Contraction
What does the platelet release after contraction?
Granules
What is found within granules that cause platelets to stick to vessel wall and eachother?
ADP and thromboxane A2
Platelet plug will stop what kind of bleeding?
Small breaks - nose, skin
3 major steps of clot formation?
1) Activation of prothrombin activator (Xa)
2) Activation of thrombin
3) Creation of fibrin from fibrinogen
What is clot retraction and function?
- Get rid of excess fluid
- Solidify clot
What is required for clot retraction?
Platelets
Platelets express what for clot retraction, function?
Express Fibrin receptor, binds fibrin polymer together
What pulls the fibrin together?
Platelets contain actin and myosin, which causes a contraction
What do platelets secret for repair of damage?
Platelet-derived Growth Factor
What does platelet-derived growth factor do?
Stimulates fibroblasts to grow into area
Fibroblasts differentiate into?
Smooth muscle to close hole
Where is plasminogen made?
Liver
