Hemostasis

Question 1

What is primary hemostasis?

Answer 1

Aggregation of platelets at injury site, forming a plug

Question 2

What is secondary hemostasis?

Answer 2

Initial platelet plug is enlarged and stabilized by adding a structural matrix of fibrin (coagulation cascade)

Question 3

What is antithrombosis?

Answer 3

Process of stopping clot formation once an effective clot has formed.

Question 4

What is fibrinolysis?

Answer 4

The degradation of the clot to restore normal blood flow.

Question 5

What are platelets derived from?

Answer 5

Megakaryocytes

Question 6

What hormone is responsible for signaling platelet production and where is it generated?

Answer 6

Thrombopoietin,and it is generated in the kidney and liver

Question 7

How is Thrombopoietin activity regulated?

Answer 7

Platelets express thrombopoietin receptors as well as megakaryocytes.

When there is a high amount of circulating platelets, thrombopoietin becomes primarily bound to platelets, which consume the signal preventing it reaching megakaryocytes.

When there is a low amount of circulating platelets, thrombopoietin is not getting destroyed by platelets and instead binds with megakaryocytes, signaling platelet production.

Question 8

What does von Willebrand factor do?

Answer 8

It is a circulating plasma protein that binds to exposed collagen when a vessel injury occurs.

When bound to the collagen, it undergoes a conformational change that allows for platelet binding.

Question 9

What does platelet-derived growth factor do?

Answer 9

It induces fibroblasts to grow in areas of damage.

Fibroblasts become smooth muscle and endothelial cells to close the hole.

Question 10

What does plasmin do?

Answer 10

Breaks apart fibrin polymers, destroying clots

Question 11

How is plasmin regulated?

Answer 11

Plasminogen is the inactive form that circulates in the blood.

Damaged tissue releases Tissue Plasminogen Activator (tPA) which will normally form active plasmin from plasminogen, allowing destruction of clots.

However, tPA inhibitor (also circulating in the blood) prevents this from happening (ensuring the clot has had sufficient time to fix the hole).

Question 12

How is tPA inhibitor regulated?

Answer 12

Thrombin activates Protein C

Activated Protein C inactivates tPA inhibitor, allowing Plasmin activating and destruction of fibrin polymers.

Question 13

Describe the Extrinsic Pathway

Answer 13

Tissue factor (III) promotes the activation of VII to VIIa and forms a complex with it.

VIIa/III complex activates X to Xa.

Question 14

Describe the Intrinsic Pathway

Answer 14

XII is activated to XIIa.
XIIa catalyzes the activation of XI to XIa.
XI catalyzes the activation of IX to IXa.
IXa forms a complex with VIIIa, which then activates X to Xa

Question 15

Describe the Common Pathway

Answer 15

Xa, with the help of Va, catalyzes the activation of II (Prothrombin) to IIa (Thrombin).

IIa catalyzes the activation of I (Fibrinogen) to Ia (Fibrin) and also catalyzes the activation of XIII to XIIIa

XIIIa catalyzes the formation of cross-linked fibrin strands

Question 16

What factors does Fibrin (IIa) help activate?

Answer 16

Factor V
Factor VII
Factor VIII
Factor XI
Factor XIII

Question 17

What does Protein C promote and how does it do this?

Answer 17

Protein C promotes anticoagulation by degrading Factors V and VII as well as by inactivating tPA (tissue plasminogen activator) inhibitor.

Question 18

What are the Vitamin K dependent factors and what effect does Vitamin K deficiency have on coagulation?

Answer 18

Factor II, Factor VII, Factor IX, and Factor X, as well as Protein C.

Vitamin K deficiency reduces the ability to produce blood clots.

Question 19

What molecules together form Tenase?

Answer 19

Factor IXa, Factor VIIIa, and Ca2+

Question 20

What molecules together form Prothrombinase?

Answer 20

Factor Xa, factor Va, and Ca2+

Question 21

What does an abnormal Prothrombin Time (PT) indicate?

Answer 21

Indicates there is a problem with either the factors in the common pathway (X, II, V, or I) OR the extrinsic pathway (VII)

Question 22

What does an abnormal Partial Thromboplastin Time (PTT) indicate?

Answer 22

Indicates there is a problem with either the factors of the common pathway (X, V, II, or I) OR the intrinsic pathway (XII, XI, IX, or VIII).

Question 23

What does Heparin do?

Answer 23

It is an anticoagulant. Blocks activity of Factors IIa, IX, and Xa.

Question 24

What is hemophilia A?

Answer 24

A deficiency of Factor VIII

Question 25

What is hemophilia B?

Answer 25

A deficiency of Factor IX

Question 26

What does Warfarin do?

Answer 26

Anticoagulant that blocks the synthesis of vitamin K dependent factors

Factors II, VII, IX, and X