Page 561 - Clinical Hematology_ Theory _ Procedures ( PDFDrive )

CHAPTER 27 ■ Principles of Hemostasis and Thrombosis: Blood Coagulation Factors and Natural Coagulant Systems 545

T e ro uction o rotein S co actor by en othe ia ce s is ■ So ub e b oo coagu ation actors are critica co onents

be ieve to ay a signi cant regu atory ro e in the initiation, in the or ation o a thro bus.

ro agation, an su ression o he ostasis an thro bosis. ■ Te brinogen grou consists o actors I, V, VIII, an

En othe ia ce s synthesize an secrete rotein S an inter- XIII. T ese actors are consu e uring the rocess o

na ize this o ecu e in a yna ic anner. Once ow eve s o coagu ation.

APC are or e by thro bin on the en othe ia sur ace, it ■ T e rothro bin grou consists o actors II, VII, IX, an

ay be in roxi ity to rotein S (rece tor), resu ting in the X. A these actors are e en ent on vita in K uring

or ation o an active, stab e inactivator co ex or actors their synthesis.

VIIIa an Va. ■ Te contact grou consists o actors XI, XII, reka i-

krein (F etcher actor), an HMWK (Fitzgera actor).

MODERN VIEW OF HEMOS ASIS Tese actors are invo ve in the intrinsic coagu ation
athway.

Since the i -1960s, a variety o key co onents o the ■ Initiation o the coagu ation rocess ay occur via one

coagu ation syste (e.g., rotein C athway) an other o two athways: the extrinsic athway an the intrinsic

he ostasis-re ate actors (e.g., rotein Z) have been is- athway.

covere . Historica y, the intrinsic athway was consi ere ■ Regar ess o the initiating athway, the two athways con-

to be the ost i ortant athway. One ajor weakness o verge into a na co on athway. T e outco e o this

this athway has been that this athway cou not correct y rocess is the conversion o circu ating inso ub e coagu a-

ex ain the questionab e or even nonexistent ro e o HMWK, tion actors into a ge atinous brin c ot with entra e

reka ikrein, an actor XII (Hage an’s actor) in the initia- b oo ce s, a b oo c ot.

tion o coagu ation. ■ As re air o a age tissue takes ace, the c ot is yse

Recent y, tissue actor an actor VIIa in the extrinsic an the articu ate atter is re ove by the ononuc ear

athway have been e onstrate to be the ajor athway hagocytic syste .

or activation o coagu ation. It has a so been iscovere that ■ A variety o aboratory roce ures are va uab e in assess-

thro bin has a ar ore i ortant ro e as an activator an ing coagu ation actors. Genera roce ures inc u e the

an inhibitor. T ro bin is AP , the P , the thro bin ti e, an quantitative brin-
ogen concentration assay. More s ecia ize or c assic ro-

■ T e key enzy e in the conversion o so ub e brinogen ce ures can be er or e in s ecia circu stances.
into brin

■ Require or the activation o the rotein C syste , which Normal Protective Mechanisms Against
own-regu ates he ostasis Thrombosis

■ Require or the activation o thro bin-activatab e bri-
no yis inhibitor, which is invo ve in the own-regu ation ■ In the b oo circu ation, the re is osition to thro bosis

o the brino ytic rocess e en s on the ba ance between rocoagu ant an anti-

coagu ant actors.
Te cu u ative resu t o new iscoveries in coagu ation T e nor a f ow o b oo revents the accu u ation o

has e to the eve o ent o a ternative sche atic re re- ■ rocoagu ant ateria .

sentations o the athways that better re resent the nor a ■ T is echanis re uces the chance o oca brin or a-

in vivo rocess o coagu ation.
tion. Another nor a echanis against ina ro riate

thro bosis is the re ova ro the b oo o activate

c otting actors by he atocytes. T is rocess, a ong with
NOTE: This is a good time to complete end of chapter the natura y occurring inhibitors, i its intravascu ar

Review Questions.
c otting an brino ysis by inactivation o such actors as

XIa, IXa, Xa, an IIa.

■ Re ova o articu ate ateria by the ce s o the ono-
CHAP ER HIGHLIGH S nuc ear hagocytic syste is a so i ortant in reventing

the initiation o coagu ation.
Blood Coagulation Factors

■ Te in vivo existence o natura anticoagu ant syste s

■ B ee ing ro s a b oo vesse s ay be sto e by is essentia to revent thro bosis. T ese natura antico-
vasoconstriction an the or ation o a ate et ug. agu ant syste s inc u e A , HC-II, an rotein C an

■ For ation o a c ot (thro bus) usua y occurs as art o its co actor, rotein S. A an HC-II are serine rotease
the nor a rocess o he ostasis. inhibitors.