18.5 Hemostasis

vascular spasm.

The first step in hemostasis is ________.

inadequate production of clotting factors.

Hemophilia is characterized by ________.

common pathway.

Prothrombin is converted to thrombin during the ________.

Clotting factors flow through the blood vessels in their inactive state. The endothelium does not have thrombogenic tissue factor to activate clotting factors.

View these animations to explore the intrinsic, extrinsic, and common pathways that are involved the process of coagulation. The coagulation cascade restores hemostasis by activating coagulation factors in the presence of an injury. How does the endothelium of the blood vessel walls prevent the blood from coagulating as it flows through the blood vessels?

When blood contacts glass, the intrinsic coagulation pathway is initiated. This leads to the common pathway, and the blood clots. Within about 30 minutes, the clot begins to shrink. After an hour, it is about half its original size. Its heavier weight will cause it to fall to the bottom of the tube during centrifugation, allowing the lab technician to harvest the serum remaining at the top.

A lab technician collects a blood sample in a glass tube. After about an hour, she harvests serum to continue her blood analysis. Explain what has happened during the hour that the sample was in the glass tube.

In a thrombotic stroke, a blood vessel to the brain has been blocked by a thrombus, an aggregation of platelets and erythrocytes within a blood vessel. A thrombolytic agent is a medication that promotes the breakup of thrombi.

Explain why administration of a thrombolytic agent is a first intervention for someone who has suffered a thrombotic stroke.