Contents1 )Hemostasis

2 )Vascular Phase

3 )Platelet Phase

4 )Clot formation

5 )Clot retraction

6 )Fibrinolysis

Hemostasis

Haima + Stasis

Prevent blood loss

*Hemostasis is process of forming clots in walls of damaged blood vessels and

preventing blood loss, while maintaining

blood in a fluid state within vascular

system

•Stages of Hemostasis

I. VASCULAR CONSTRICTION

•1 )Immediately blood vessel is cut or ruptured. 2) Stimulus of trauma to vessel causes wall of

vessel to contract .•

3 )This immediately reduces the flow of blood from vessel rupture.

4 )More a vessel is traumatized. 5) The greater the degree of spasm. 6) This local vascular spasm can last for many minutes or even hours

Vascular Phase

II. FORMATION OFTHE PLATELET PLUG

When platelets come in contact with a damaged vascular surface, they immediately change their

characteristics :

1 )Begin to swell

2 )Assume irregular forms with numerous irradiating pseudopods protruding from their surfaces;

•

3 )Their contractile proteins contract and cause release of granules contain multiple active

factors ;

4)They become sticky so that they stick to collagen fibers;

III. BLOOD COAGULATION IN THE RUPTURED VESSEL

•1 )Clot begins to develop in 15 to 20 seconds if trauma of vascular wall severe 2)And in 1 to 2 minutes if the trauma minor 3) Activator substances both from traumatized vascular wall and from platelets and blood proteins adhering to traumatized vascular wall initiate clotting process..

4 )Within 3 to 6 minutes after rupture of a vessel, if vessel opening is not too large, entire opening or broken end of vessel is filled with clot.

5 )After 20 minutes to

an hour, clot retracts; this closes vessel.

CLOT•1 )CLOT is composed of meshwork of fibrin fibers

running in all directions and entrapping blood cells, platelets, and plasma .

• 2 )Fibrin fibers also adhere to damaged surfaces of

blood vessels; therefore, the blood clot becomes adherent to any vascular opening and thereby prevents blood loss.

Coagulation process1 )When tissues

are exposed enzyme thrombin is released.

2 )Thrombin

activates clotting factor in platelets causing them to become sticky.

Coagulation Process

3 )The platelets begin to stick together at wound site binding to exposed fibers.

4 )Platelets release

several chemicals and change their shape to fit formation of plug..

5 )Then, a fibrin mesh forms and insures the clot will

stay .

6 )Finally, blood clot must dissolve in order to restore normal blood flow to the vessel

CLOT RETRACTION•1 )Platelets are become attached to fibrin, fibers in

such a way that they actually bond different fibers together.

• 2) Platelets release procoagulant substances, one of

which is fibrin-stabilizing factor, which causes more and more cross-linking bonds between adjacent fibrin fibers.

• 3 )Platelets themselves contribute directly to clot

contraction by activating platelet thrombosthenin, actin, and myosin molecules )contractile proteins) and cause strong contraction of the platelet attached to the fibrin.

•4 )This helps compress fibrin meshwork into a smaller mass. 5) Contraction is activated or accelerated by thrombin as well as by

calcium ions released from platelets .

•6 )As clot retracts,edges of broken blood vessel are pulled together, thus contributing to ultimate state of haemostasis

Fibrinolysis

Process wherein a fibrin clot, product of coagulation, is broken down. Its main enzyme plasmin cuts fibrin mesh at various places, leading to production of circulating fragments That are cleared by other proteases or by the kidney and liver

HEMOSTASIS

FIBROUS ORGANIZATION(DISSOLUTION OF THE CLOT)

1 )It can become invaded by fibroblasts, which subsequently form connective tissue all through

clot .

2 )it can dissolve .•

The usual course for a clot that forms in a small hole of a vessel wall is invasion by fibroblasts, beginning within a few hours after clot is formed. This continues to complete organization of the clot into fibrous tissue within about 1 to 2 weeks.

When additional blood coagulates to form a larger clot such as blood that has leaked into tissues, special substances within the clot itself usually become activated And these then function as enzymes to dissolve the clot.

How does the blood clotting process work_ - DnaTube.com - Scientific Video and Animation Site.flv

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