Human Physiology, 14th edition (2016)

416 Chapter 13

plug. The intrinsic clotting sequence is shown on the right side

of figure 13.9.

The extrinsic pathway of clot formation is initiated

by tissue factor (or tissue thromboplastin, also known as

factor III ), a membrane glycoprotein found inside the walls

steps result in the conversion of an inactive glycoprotein, called
prothrombin, into the active enzyme thrombin. Thrombin
converts the soluble protein fibrinogen into fibrin monomers.
These monomers are joined together to produce the insoluble
fibrin polymers that form a meshwork supporting the platelet

Factor Name Function Pathway

I Fibrinogen Converted to fibrin Common

II Prothrombin Converted to thrombin (enzyme) Common

III Tissue thromboplastin Cofactor Extrinsic

IV Calcium ions (Ca^21 ) Cofactor Intrinsic, extrinsic, and common

V Proaccelerin Cofactor Common

VII* Proconvertin Enzyme Extrinsic

VIII Antihemophilic factor Cofactor Intrinsic

IX Plasma thromboplastin component; Christmas factor Enzyme Intrinsic

X Stuart-Prower factor Enzyme Common

XI Plasma thromboplastin antecedent Enzyme Intrinsic

XII Hageman factor Enzyme Intrinsic

XIII Fibrin stabilizing factor Enzyme Common

*Factor VI is no longer referenced; it is now believed to be the same substance as activated factor V.

Table 13.4 | The Plasma Clotting Factors

Figure 13.9 The clotting pathways. (1) The extrinsic clotting pathway is initiated by the release of tissue factor. (2) The
intrinsic clotting pathway is initiated by the activation of factor XII by contact with collagen or glass. (3) Extrinsic and intrinsic clotting
pathways converge when they activate factor X, eventually leading to the formation of fibrin.

Extrinsic pathway Intrinsic pathway

Activator:

tissue factor

VII VII activated

VII complex

(VII, tissue

factor,

calcium,

phospholipids)

Activators:

collagen, glass,

and others

XII XII activated

XI XI activated

IX IX activated

VIII complex

(VIII, IX activated,

calcium, phospholipids)

Common

pathway

X X activated

V complex

(V, X activated,

calcium,

phospholipids)

Prothrombin Thrombin

Fibrinogen Fibrin

Fibrin

XIII polymer

1 2

3