Page 546 - Clinical Hematology_ Theory _ Procedures ( PDFDrive )

530 PART 7 ■ Principles and Disorders of Hemostasis and Thrombosis

Factor XIII (Fibrin-Stabilizing Factor) VIIa VII

Fibrin-stabi izing actor in the resence o ionize ca ciu Complex T. Thromboplastin
2+
ro uces a stabi ize brin c ot. Ca

Fine ibrin c ots actor XIII +

ca ciu ions → stab e ibrin c ot

Prekallikrein (also Know n as Fletcher Factor)
X Xa

■ Preka ikrein (PK) is a is serine rotease coagu ation actor Complex Va V
that co exes with high o ecu ar weight kininogen. PK Ca 2+

rece es ka ikrein which activates kinins. PK is c eave PF 3
to ro uce ka ikrein by activate Factor XII (Hage an

Factor).

■ Patients with reka ikrein (PK) e ciency exhibit severe y

ro onge activate artia thro bo astin ti e (AP )
resu ts but e onstrate no b ee ing sy to s. Because II IIa (Thrombin)

this is an inherite isor er, any e bers o a a i y
can have a PK e ciency as was the case in the origina y Fibrinogen Fibrin

iscovere Kentucky a i y na e F etcher.

■ High o ecu ar weight kininogen (HMWK) is a so known FIGURE 27.2 Extrinsic athway o coagu ation. (PF3, ate et ac-
tor 3.)
as Fitzgera actor. It is a rotein ro uce by the iver
an is invo ve in the ear y ste s o the intrinsic coagu a-

tion athway. HMWK unctions as a co actor an bin s Coagulation Pathways
with reka ikrein an actor XI to he aci itate their acti-

vation by actor XIIa. Initiation o c otting begins with either the extrinsic or the

■ T e kininogens ( ow an high o ecu ar weight) are a so intrinsic athway. Factor X activation is the oint o conver-

invo ve in the kinin-ka ikrein syste an unction to gence. Factor X can be activate by either o the two athways
inhibit thro bin activation o ate ets an sti u ate ib- an subsequent y cata yzes the conversion o rothro bin to

eration o nitric oxi e, rostacyc in, an tissue as ino- thro bin.
gen activator
The Extrinsic Coagulation Pathway

Te extrinsic athway (Fig. 27.2) is initiate by the entry

NOTE: This is a good time to review the de nitions of the Key o tissue thro bo astin into the circu ating b oo . issue

Terms in the Glossary and . It is also a good time to thro bo astin is erive ro hos ho i o roteins an

complete Review Questions related to preceding content. organe e e branes ro isru te tissue ce s. T ese
e brane i o roteins, ter e tissue factors, are nor a y

extrinsic to the circu ation. P ate et hos ho i i s are not

The Plasma Clot–Based Mechanism of necessary or activation o the extrinsic athway because tis-

Coagulation sue actor su ies its own hos ho i i s.
Factor VII bin s to these hos ho i i s in the tissue ce

Many che ica reactions occur in he ostasis, ro the ini- e branes an is activate to actor VIIa, a otent enzy e

tia sti u us that triggere b ee ing to the na or ation o ca ab e o activating actor X to Xa in the resence o ionize

a stab e c ot. o un erstan the rocess ore easi y, ortions ca ciu . T e activity o the tissue actor – actor VII co ex

o the nor a coagu ation sequence are arti cia y segregate see s to be arge y e en ent on the concentration o tis-

into s a er sections such as the extrinsic an intrinsic ath- sue thro bo astin. T e roteo ytic c eavage o actor VIIa

ways. T ese athways are not actua hysio ogica athways by actor Xa resu ts in inactivation o actor VIIa. Factor VII

o he ostasis but a ow or the grou ing o actor e ects an artici ates only in the extrinsic athway. Me branes that

the ocusing o aboratory assays. enter the circu ation a so rovi e a sur ace or the attach-

T e initiation o the coagu ation rocess ay occur via ent an activation o actors II an V. T e na ste is the

one o two athways: the extrinsic pathway an the intrinsic conversion o brinogen to brin by thro bin.

pathway. Regar ess o the initiating athway, the two ath-

ways converge into a na co on athway. T e outco e o The Intrinsic Coagulation Pathway

this rocess is the conversion o circu ating inso ub e coag- T e intrinsic athway (Fig. 27.3) invo ves the contact activa-

u ation actors into a ge atinous brin c ot with entra e tion actors reka ikrein, HMWK, actor XII, an actor XI.

b oo ce s, a b oo c ot. As re air o a age tissue takes T ese actors interact on a sur ace to activate actor IX to

ace, the c ot is yse an the articu ate atter is re ove IXa. Factor IXa reacts with actor VIII, PF 3, an ca ciu to

by the ononuc ear hagocytic syste . activate actor X to Xa. In the resence o actor V, actor Xa