Hemostasis

Question 1

What is hemostasis?

Answer 1

Sequence of responses to stop bleeding

Prevents small hemorrhages

Question 2

Mechanisms to reduce blood loss (x3)

Answer 2

Vascular spasm: vasoconstriction of SM of BVs –> reduces BF through damaged area

Platelet plug formation

Blot clotting: coagulation cascade

Question 3

What stimulates vascular spasm?

Answer 3

Thromboxane A2 released by platelets

Question 4

What makes up primary hemostasis?

Answer 4

Vascular spam + platelet plug formation

Question 5

What makes up secondary hemostasis?

Answer 5

Blood clotting

Question 6

Platelet production process

Answer 6

Pluripotent stem cell –> myeloid stem cell –> megakaryoblast –> megakaryocyte –> platelet

Question 7

Functions of platelets

Answer 7

Stop blood loss from damaged BVs

Form a platelet plug, release chemicals that promote: blood clots & vascular spasms

Question 8

Steps of platelet plug formation (x3)

Answer 8

Adhesion, release, aggregation

Question 9

What occurs during platelet adhesion?

Answer 9

Damaged endothelium exposes underlying collagen fibers

Platelets adhere to collagen –> platelet activation

Question 10

What occurs during platelet release?

Answer 10

ADP, thromboxane A2 and serotonin are released by platelets after activation

ADP makes platelets sticky

ADP and TA2 activate other platelets the were recruited

TA2 and serotonin cause vasoconstriction –> vascular spasm

Question 11

What occurs during platelet aggregation?

Answer 11

Platelet plug is formed; loose but will be reinforced with a fibrin net during coagulation

Question 12

Blood clotting is a…

Answer 12

Positive feedback cycle

Question 13

What is a thrombus?

Answer 13

Clot inside a vessel –> remains at site of origin

Question 14

What is a thromboembolus?

Answer 14

Blood clot that travels in the bloodstream

Question 15

Extrinsic pathway: coagulation cascade

Answer 15

Occurs rapidly

Tissue factors leak from outside cells –> BVs

Tissue factors + calcium = activation of factor X

Factor X + factor V (in the presence of calcium) = prothrombinase

Question 16

Intrinsic pathway: coagulation cascade

Answer 16

Slower than extrinsic

Activate if there is damage inside of BVs

Blood comes into contact with collagen = activation of factor XII

Factor XII + calcium = factor X activation

Phospholipids + calcium also activate factor X

Factor X + factor V + calcium = prothrombinase

Question 17

Common pathway: coagulation cascade

Answer 17

Prothrombinase in the presence of calcium turns prothrombin –> thrombin

Question 18

Formation of insoluble fibrin

Answer 18

Thrombin + calcium + fibrinogen –> loose fibrin threads

Factor XIII is released by platelets (thrombin activates it)

Activated factor XIII strengthens the loose fibrin threads (catalyzing cross linkages)

Question 19

Fibrinolysis (clot lysis)

Answer 19

Plasminogen in the presence of activated XII and tissue plasminogen activator –> plasmin

Plasmin breaks down cross-linked fibrin threads & inactivates substances in the clotting cascade

Question 20

Three ways to prevent/break up blood clots

Answer 20

Antiplatelets

Anticoagulants

Thrombolytics

Question 21

What do antiplatelets do? + Example

Answer 21

Prevent platelet plug formation

Aspirin

Question 22

What do anticoagulants do? + Example

Answer 22

Suppress or prevent blood clotting (prevents coagulation cascade & formation of fibrin net

Heparin, Warfarin and Vitamin K antagonists

Question 23

Vitamin K and blood clotting

Answer 23

Vitamin K is necessary for the synthesis of clotting factors

Vitamin K antagonists + Warfarin –> block activity of Vit K

Question 24

What do thrombolytics do? + Example

Answer 24

Break ip clots

Tissue plasminogen activator (tPA)

Streptokinase (enzyme that activates plasminogen)