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Hematologi 2Hematologi 2

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Proses penghentian perdarahan secara spontan dari pembuluh darah yang mengalami kerusakan (luka).

HEMOSTASISHEMOSTASIS(Haima=darah,

stasis=berhenti)

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HEMOSTASISHEMOSTASISHemostasis adalah proses yang dilakukan oleh tubuh untuk melindungi diri dari proses pendarahan. Hemostasis adalah mekanisme alami dari tubuh untuk menghentikan kehilangan darah yang berlebihan

“is the process which retains the blood within the vascular system”. Hemostatic process “is designed to repair the break and arrest hemorrhage”.

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HEMOSTASIS :HEMOSTASIS :

The most immediate response to bleeding are from:

1. VascularBy Vasoconstriction mechanism, which decreases the blood flow through the injured blood vessel

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HEMOSTASIS :HEMOSTASIS :The most immediate response to bleeding are

from:

2. PlateletsPlatelets clump together and adhere to the injured vessel in this area in order to form a plug, and further inhibit bleeding

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HEMOSTASIS :HEMOSTASIS :

The most immediate response to bleeding are from:

3. The Coagulation factorsBy forming a fibrin meshwork or clot to stop the bleeding completely

• Mekanisme Hemostasis

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• Hemostasis is a process which causes bleeding to stop, meaning to keep blood within a damaged blood vessel (the opposite of hemostasis is hemorrhage)

Hemostasis bertujuan untuk menjaga agar darah tetap cair di dalam pembuluh, menghentikan perdarahan, mencegah kehilangan darah karena luka, memperbaiki aliran darah selama proses penyembuhan luka. 8

• Vasoconstriction of a damaged blood vessel slows the flow of blood and thus helps to limit blood loss. This process is mediated by:1. Local controls. Vasoconstrictors such

as thromboxane are released at the site of the injury.

2. Systemic control. Epinephrine released by the adrenal glands stimulates general vasoconstriction.

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Formation of a Platelet Plug.

•When a blood vessel is damaged, the blood is exposed to collagen fibers. Platelets stick to collagen and become activated. Activated platelets release chemicals such as ADP, and thromboxane, that cause the aggregation.

•It is essential that platelets become activated only at the site of a broken vessel. Otherwise activated platelets would form plugs and induce clots in inapropriate places. Healthy vessels secrete an enzyme called prostacyclin that functions to inhibit platelet activation and aggregation.

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Clotting of Blood

•The blood contains about a dozen clotting factors. These factors are proteins that exist in the blood in an inactive state, but can be called into action when tissues or blood vessels are damaged. The activation of clotting factors occurs in a sequential manner. The first factor in the sequence activates the second factor, which activates the third factor and so on. This series of reactions is called the clotting cascade.

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Clotting of Blood

•Blood clotting is the transformation of liquid blood into a semisolid gel. Clots are made from fibers (polymers) of a protein called fibrin. Fibrin monomers come from an inactive precursor called fibrinogen.

•This process requires thrombin, the enzyme that converts fibrinogen to fibrin. This process also requires calcium, which acts as a kind of glue to hold the fibrin monomers to each other to form the polymeric fiber. The fibrin fibers form a loose meshwork that is stabilized by clotting factor XIII. The stabilized meshwork of fibrin fibers traps erythrocytes, thus forming a clot that stops the flow of blood.

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