J

Factor X

Activates

Factor V

Factor X

Activates

Activates

Factor X

Activates

pIateIet phosphoIipids

Factor V

Prothrombin activator

Prothrombin (Factor II)

Converts

Fibrinogen (Factor I)

Figure 14.19

Schematic of blood-clotting mechanisms.

Thrombin (Factor IIa)

Converts

Fibrin

Stabilizes

Factor XIII

Fibrin cIot

Abnormal clot formations are often associated with conditions that change the endothelial linings of vessels. For example, in atherosclerosis, accumulations of fatty deposits change arterial linings, sometimes initiating inappropriate clotting. This is the most common cause of thrombosis in medium-sized arteries (fig. 14.20).

Coagulation may also occur in blood that is flowing too slowly. The concentration of clot-promoting substances may increase to a critical level instead of being carried away by more rapidly moving blood, and a clot may form. This event is the usual cause of thrombosis in

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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