hemostasis (steps of). 1. vascular spasms in response to damage of an artery or arteriole the rings...
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HEMOSTASIS (STEPS OF)
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
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)
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.
Platelet Plug Formation
Process Diagrams Step-by-Step
Copyright © 2007 by John Wiley & Sons, Inc.
1
Red blood cell
Platelet
Collagen fibersand damagedendothelium
Platelet adhesion1
1
2
Red blood cell
Platelet
Collagen fibersand damagedendothelium
Liberated ADP,serotonin, andthromboxane A2
Platelet adhesion1
Platelet release reaction2
1
2
3
Red blood cell
Platelet
Collagen fibersand damagedendothelium
Liberated ADP,serotonin, andthromboxane A2
Platelet plug
Platelet adhesion1
Platelet release reaction2
Platelet aggregation3
3. Blood Clotting
• Takes advantage of the fact that blood only remains a liquid when contained in vessels
• The first reactions form the molecule prothrombin (all controlled by thromboplastin)
• Thromboplastin converts prothrombin into an enzyme called thrombin
• Thrombin converts soluble fibrinogen into insoluble fibrin which forms the threads of the clot
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.
Blood Clotting
Process Diagrams Step-by-Step
Copyright © 2007 by John Wiley & Sons, Inc.
Tissue trauma
Tissuefactor(TF)
Blood trauma
Damagedendothelial cellsexpose collagenfibers
(a) Extrinsic pathway (b) Intrinsic pathway
Activated XII
Ca2+
Damagedplatelets
Ca2+
Plateletphospholipids
Activated X
Activatedplatelets
Activated X
PROTHROMBINASECa2+
VCa2+
V
1
Tissue trauma
Tissuefactor(TF)
Blood trauma
Damagedendothelial cellsexpose collagenfibers
(a) Extrinsic pathway (b) Intrinsic pathway
Activated XII
Ca2+
Damagedplatelets
Ca2+
Plateletphospholipids
Activated X
Activatedplatelets
Activated X
PROTHROMBINASECa2+
VCa2+
Prothrombin(II)
Ca2+
THROMBIN
(c) Commonpathway
V
1
2
+
+
Tissue trauma
Tissuefactor(TF)
Blood trauma
Damagedendothelial cellsexpose collagenfibers
(a) Extrinsic pathway (b) Intrinsic pathway
Activated XII
Ca2+
Damagedplatelets
Ca2+
Plateletphospholipids
Activated X
Activatedplatelets
Activated X
PROTHROMBINASECa2+
VCa2+
Prothrombin(II)
Ca2+
THROMBIN
Ca2+
Loose fibrinthreads
STRENGTHENEDFIBRIN THREADS
Activated XIIIFibrinogen(I)
XIII
(c) Commonpathway
V
1
2
3
+
+