1. HEMOSTASIS (Stages of Blood Clotting)‏

2. 1. Vascular Spasms
In response to damage of an artery or arteriole the rings of smooth muscle in the walls of the vessel begin to spasm immediately
This reduces blood loss and gives time for other mechanisms to begin
The spasms are caused by chemicals that are released by the smooth muscle, platelets, and pain receptors in the area

4. 2. Platelet Plug Formation
Platelets come into contact with the damaged vessel and stick to the parts of it that are torn (called platelet adhesion)‏
The adhesion activates the platelets and they change
Each platelet extends projections that allow them to touch one anther and they begin to empty the contents of their vesicles (called platelet release reaction)‏

5. 2. Cont.
ADP and thromboxane A2 are released to activate nearby platelets
Serotonin and thromboxane A2 cause vasoconstriction of the blood vessel which in turn reduces blood flow from the damaged vessel
The ADP makes the platelets nearby sticky and they migrate and join the first responder platelets (platelet aggregation)‏
This will lead to the formation of a solid mass called the platelet plug.

8. Platelet Plug Formation
Process Diagrams Step-by-Step
Copyright © 2007 by John Wiley & Sons, Inc.

9. 1 Red blood cell Platelet Collagen fibers and damaged endothelium 1
Platelet adhesion

10. 1 2 Red blood cell Platelet Collagen fibers and damaged endothelium 1
Platelet adhesion
Liberated ADP,
serotonin, and
thromboxane A2 2 2
Platelet release reaction

11. 1 2 3 Red blood cell Platelet Collagen fibers and damaged endothelium
Platelet adhesion
Liberated ADP,
serotonin, and
thromboxane A2 2 2
Platelet release reaction
Platelet plug 3 3
Platelet aggregation

12. 3. Blood Clotting (Coagulation Events)
Takes advantage of the fact that blood only remains a liquid when contained in vessels
Dependent on injured tissues releasing tissue factor (TF) which interacts with PF3 on platelets
The first reactions form the molecule prothrombin (all controlled by thromboplastin)‏
Thromboplastin converts prothrombin into an enzyme called thrombin via reaction with Ca2+ ions
Thrombin converts soluble fibrinogen into insoluble fibrin which forms the threads of the clot

13. After Affects
Once the clot is formed it will slowly begin to retract and pull the damaged ends of the vessel together
During this phase some blood serum can escape but the actual blood cells cannot
Eventually fibroblasts will begin to form new tissues in the area and new endothelial cells will repair the damaged lining
In the end the vessel will return back to normal.
Calcium ions (Ca2+) are the main ion involved in the clotting process

15. Process Diagrams Step-by-Step
Blood Clotting
Process Diagrams Step-by-Step
Copyright © 2007 by John Wiley & Sons, Inc.

16. 1 PROTHROMBINASE (a) Extrinsic pathway (b) Intrinsic pathway
Tissue trauma
Blood trauma
Damaged
endothelial cells
expose collagen
fibers
Tissue
factor
(TF)
Damaged
platelets
Activated XII
Activated
platelets
Ca2+
Ca2+
Platelet
phospholipids
Activated X
Activated X V V
Ca2+
Ca2+ 1
PROTHROMBINASE

17. + + 1 PROTHROMBINASE THROMBIN 2 (a) Extrinsic pathway
(b) Intrinsic pathway
Tissue trauma
Blood trauma
Damaged
endothelial cells
expose collagen
fibers
Tissue
factor
(TF)
Damaged
platelets
Activated XII
Activated
platelets
Ca2+
Ca2+ +
Platelet
phospholipids
Activated X
Activated X V V +
Ca2+
Ca2+ 1
PROTHROMBINASE
(c) Common
pathway
Ca2+
Prothrombin
(II)
THROMBIN 2

18. + + 1 PROTHROMBINASE THROMBIN 2 STRENGTHENED 3 FIBRIN THREADS
(a) Extrinsic pathway
(b) Intrinsic pathway
Tissue trauma
Blood trauma
Damaged
endothelial cells
expose collagen
fibers
Tissue
factor
(TF)
Damaged
platelets
Activated XII
Activated
platelets
Ca2+
Ca2+ +
Platelet
phospholipids
Activated X
Activated X V V +
Ca2+
Ca2+ 1
PROTHROMBINASE
(c) Common
pathway
Ca2+
Prothrombin
(II)
THROMBIN 2
Ca2+
XIII
Fibrinogen
(I)
Activated XIII
Loose fibrin
threads
STRENGTHENED 3
FIBRIN THREADS