Chapter 18.5, Problem 13AYLO

Summary Introduction

To discuss:

The reason why spontaneous clotting usually occurs in veins, the danger of travelling blood clots, and the reason for the clots lodging in the lungs.

Introduction:

Hemostasis is the process by which the body stops blood loss, and there are three major hemostatic mechanisms: spasm of blood vessels, formation of platelet plug, and clotting of blood. When an injury occurs, local blood vessels first constrict to reduce blood flow to the area; next, platelets adhere to the collagen fibers of the vessel wall exposed by the injury and release substances that further promote platelet aggregation and vasoconstriction such as serotonin, adenosine diphosphate, and thromboxane A₂; and subsequently, the coagulation of blood occurs. These mechanisms together help to stop blood loss.

Blood coagulation itself consists of two pathways (the intrinsic and extrinsic mechanisms) that reach a common convergence point after following different steps. The common convergence point of the two pathways is reached when factor X is formed. This continues on to the end point, which is the formation of fibrin polymer molecules that form the blood clot.

Disorders in blood clotting include the absence of appropriate clotting (clotting deficiency) and unwanted clotting (thrombosis).