hemostasis (steps of). 1. vascular spasms in response to damage of an artery or arteriole the rings...

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

+

+