natural anticlotting and fibrinolytic system

Question 1

def the natural anti clotting mechanisms

Answer 1

• these are mechanisms that prevent clotting inside blood vessels, breakdown any clot that do form, or both

Question 2

list anti clotting mechanisms

Answer 2

1. rapid flow of the blood
2. endothelial factor :
   - intact smooth endothelium
   - layer of glycocalyx on endothelium
   - balance between prostacyclin(PGI2) & TxA2
   - thrombomodulin
   -tissue factor pathway inhibitor (TFPI)
3. anticoagulant protein
   - protein C
   -protein S
   -anti thrombin III (heparin cofactor I)
4. thrombin removal from the blood
5. heparin
6. clot lysis

Question 3

how the rapid blood flow act as anti clotting mechanism?

Answer 3

it facilitate the removal of activated clotting factor by the circulating blood and their inactivation by the liver

Question 4

intact smooth endothelium prevents contact activation of……………

Answer 4

the intrinsic clotting system & platelet

Question 5

how the glycocalyx help in anti-clotting mechanisms?

Answer 5

it repels clotting factor & platelet

Question 6

Balance between Prostacyclin (PGI2) & Thromboxane A2 (TxA2) act as natural anti-clotting mechanism. illustrate

Answer 6

-Keeps clot formation at site of injury only and rest of vessel lumen free of clot
-PGI2 produced by healthy endothelium & inhibit the platelet aggregation & phospholipid release that initiate coagulation and oppose aggregating effect of TxA2

Question 7

illustrate the role of thrombomodulin as anti-clotting factor

Answer 7

-A protein bound with endothelium
-Binds thrombin to prevent clot formation
-Thrombomodulin-thrombin complex activates protein C that act as anticoagulant

Question 8

what’s Tissue Factor Pathway Inhibitor ?
(TFPI)

Answer 8

*Is made by the endothelial cell.
*Inactivates :
- Tissue factor / factor VIIa complex
- Factor X

Question 9

1-what’s protein C ?
2- protein C activated by ………..

Answer 9

1-A naturally occurring anticoagulant plasma protein
2-Activated by thrombomodulin-thrombin complex
-The activation is enhanced by protein S which acts as a cofactor.

Question 10

activated protein C (APC) causes ………………………..

Answer 10

-Inactivates active factors VIII, V
-Inactivates inhibitors of plasminogen
activators
-↑ formation of plasmin → helps lysis of fibrin

Question 11

what’s protein S ?

Answer 11

• vitamin K-dependent hemostatic protein
• protein C cofactor

Question 12

list function of anti-thrombin III (heparin cofactor I )

Answer 12

-Inactivation of thrombin
-Inactivation of active factors II, IX, X, XI, XII
-Its action is facilitated by heparin

Question 13

Thrombin Removal from Blood Is mediated by…………….

Answer 13

-Fibrin fibers
-Antithrombin III
► 85 –90% of thrombin is bound to fibrin, which prevents spread of thrombin (Antithrombin action of fibrin).
► Remaining amount is bound to antithrombin-III.

Question 14

def the heparin

Answer 14

-Heparin is a powerful anticoagulant, present in low concentration in blood

Question 15

what’s the role of heparin as anti-clotting factor ?

Answer 15

-When heparin combines with antithrombin III, the effectiveness of antithrombin III for removing thrombin
increases 100-1000 folds.
-Heparin + Antithrombin III complex
→ Removal of thrombin & active factors XII, XI, X, IX

Question 16

what’s Fibrinolytic System?

Answer 16

-is a plasma enzyme cascade that breaks down blood clot
- A fibrin clot is a transitory device until permanent repair of the vessel occurs

Question 17

what’s the function of Fibrinolytic System?

Answer 17

It is the physiological process for
- Clot removal
- Restriction of clotting to a limited area
→ preventing excessive intravascular coagulation

Question 18

illustrate the mechanism of fibrinolytic system

Answer 18

(1).Plasminogen (profibrinolysin)
*Is an inactive globulin
*Produced by liver
*Circulates in plasma as a plasma protein

(2). Plasminogen is converted to plasmin (fibrinolysin) by
♠ Thrombin
♠ Tissue plasminogen activator (t-PA) is released very slowly from damaged
tissues and vascular endothelium
♠ Urokinase plasminogen activator(u-PA)

(3). Plasmin is a proteolytic enzyme that digests
♣ Fibrin and fibrinogen
→ fibrin degradation products (FDP)
→ inhibit thrombin
♣ Prothrombin, factor V, factor VIII and factor XII

(4). FDP:
-Inhibits interaction between fibrinogen & thrombin
-Inhibits platelet activation &aggregation

Question 19

illustrate Regulation of Fibrinolytic System by Protein C

Answer 19

-Thrombomodulin-thrombin complex activates PC
-APC along with its cofactor PS inactivates:
♦ Active Factors V & VIII
♦ Inhibitors of t-PA → increase formation of plasmin

Question 20

“the thrombin is both procoagulant and anticoagulant”
-is that true or false? illustrate.

Answer 20

• true
• procoagulant , activate factor V & VIII
  -anticoagulant, bind to thrombomodulin forming thrombomodulin-thrombin complex which activate protein C