Hemostasis

Question 1

Stages of hemostasis

Answer 1

Vascular spasm
Platelet plug formation
Coagulation
Clot retraction
Thrombolysis

Question 2

Vascular spasm

Answer 2

Begins when blood vessel is injured and blood leaks into ECF

vasoconstriction and increased tissue pressure to decrease blood vessel diameter

Question 3

Platelet plug formation

Answer 3

A patch consisting mostly of platelets adheres to injury site to further reduce blood loss

Happens when:collagen fibers are exposed and injured endothelial cells release vWF. Together they make platelets sticky and trigger platelet activation

Question 4

Platelet activation

Answer 4

Release granules who’s content attract and activate nearby platelets causing them to aggregate

Question 5

Platelet aggregation

Answer 5

Clumping

Forms platelet plug and seals injured vessels temporarily

Question 6

Coagulation

Answer 6

Forms molecular glue: bonds platelets, endothelial cells and other formed elements

Cascade of events down two pathways: intrinsic (contact activation pathway), extrinsic (tissue factor pathway)

Converge at common pathways to activate fibrin

Question 7

Fibrin

Answer 7

Protein that converts liquid platelet plug to solid mass when activated from fibrinogen during the coagulation cascade

Question 8

Intrinsic pathway (contact activation pathway)

Answer 8

All involved clotting factors found IN blood
Activation occurs once factor XII comes in contact with exposed collagen fibers

Activates XII to XIIa—> activates XIa which activates IX

IXanand VIIIa with calcium ions activates X to Xa to complete the pathway

Question 9

Extrinsic Pathway (tissue factor pathway)

Answer 9

Initiated by factors OUTSIDE the blood-occurs simultaneously with intrinsic

Damaged subendothelial cells display tissue factor
Tissue factor activates VII to VIIa
VIIa with tissue factor and calcium ions form enzyme complex and activates X to Xa

Question 10

3 goals of coagulation cascade

Answer 10

Produce factor Xa
Produce thrombin
Produce fibrin

Question 11

Common pathway

Answer 11

Prothrombin activator X converts prothrombin to thrombin in presence of calcium ions

Leads to conversion of fibrinogen to fibrin which attracts platelets and other solids to form a stable clot

Plugs the healing site and leads to hemostasis

Question 12

Clot retraction

Answer 12

Occurs as cascade nears completion

Actin and myosin fibers contract, bring edges of wounded vessels closer together

Serum (plasma) without clotting proteins, forces out of clot

Question 13

Thrombolysis

Answer 13

Breakdown of blood clots formed in blood vessels

Begins after healing when clotting is no longer necessary