MLT 81 Chapter 12 Quiz A

What is the function of platelets in hemostasis?

• To promote vasoconstriction

• To form a platelet plug

• To initiate fibrinolysis

• To repair the endothelial lining of blood vessels

Answer explanation

Platelets play a crucial role in hemostasis, the process of stopping bleeding at the site of an injury. Their primary function is to form a platelet plug, which helps seal the damaged blood vessel and prevent further blood loss. This is achieved by adhering to the exposed collagen fibers and aggregating with other platelets, ultimately forming a stable plug.

What is the primary function of the extrinsic system of coagulation?

• To promote platelet aggregation

• To initiate vasoconstriction

• To activate the intrinsic system of coagulation

• To provide physical effects for sealing injured blood vessels

Answer explanation

The primary function of the extrinsic system of coagulation is to provide physical effects for sealing injured blood vessels. It does not promote platelet aggregation, initiate vasoconstriction, or activate the intrinsic system of coagulation. Instead, it works to form a stable clot and prevent blood loss from the injured site.

What is the role of the vascular endothelium in hemostasis?

• To promote platelet aggregation

• To initiate vasoconstriction

• To provide an inert surface for circulating procoagulants

• To repair and maintain the endothelial lining of blood vessels

Answer explanation

The vascular endothelium plays a crucial role in hemostasis by providing an inert surface for circulating procoagulants. This prevents unwanted clot formation and ensures smooth blood flow. The other options, such as promoting platelet aggregation, initiating vasoconstriction, and repairing the endothelial lining, are not the primary roles of the vascular endothelium in hemostasis.

What is the function of platelet factor 3 (PF3) in coagulation?

• To promote platelet aggregation

• To initiate vasoconstriction

• To facilitate the formation of thrombin

• To repair the endothelial lining of blood vessels

Answer explanation

Platelet Factor 3 (PF3) plays a crucial role in the coagulation process. It does not promote platelet aggregation, initiate vasoconstriction, or repair the endothelial lining of blood vessels. Instead, PF3 facilitates the formation of thrombin, a key enzyme in the coagulation cascade that converts fibrinogen to fibrin, leading to clot formation. Thus, the correct answer to the question is that PF3 facilitates the formation of thrombin.

What is thrombocytopenia?

• A condition of excessive platelet production

• A condition of inadequate platelet function

• A condition of low platelet count

• A condition of abnormal platelet distribution

Answer explanation

Thrombocytopenia is a medical condition characterized by a low platelet count. Platelets, also known as thrombocytes, are essential for blood clotting. Therefore, a decrease in their number can lead to bleeding and bruising. The other options mentioned conditions related to platelets but did not accurately describe thrombocytopenia.

What is the most immediate response of the body to bleeding?

• Platelet aggregation

• Vasoconstriction

• Fibrinolysis

• Platelet plug formation

Answer explanation

The immediate response of the body to bleeding is vasoconstriction. This is a process where the blood vessels constrict or narrow to limit blood flow to the area of injury. This is the body's first line of defense to prevent excessive blood loss. Other options like platelet aggregation and plug formation are subsequent steps in the coagulation process.

What is the role of fibrinolysis in hemostasis?

• To promote vasoconstriction

• To dissolve blood clots

• To initiate platelet aggregation

• To repair the endothelial lining of blood vessels

Answer explanation

Fibrinolysis plays a crucial role in hemostasis by dissolving blood clots. This process is essential to prevent the formation of large, obstructive clots within the blood vessels. Therefore, the correct answer to the question is 'To dissolve blood clots'.

What is the purpose of the hemostatic plug or thrombus?

• To promote vasoconstriction

• To initiate fibrinolysis

• To repair the endothelial lining of blood vessels

• To stop bleeding and seal the injured vessel

Answer explanation

The hemostatic plug or thrombus serves a crucial role in the process of hemostasis, which is the cessation of blood loss from a damaged vessel. The correct option is 'To stop bleeding and seal the injured vessel'. This is because the thrombus acts as a barrier to prevent further blood loss, effectively sealing the injured vessel and stopping the bleeding.

What is the definition of thrombocytosis?

• A decrease in circulating platelets

• An increase in circulating platelets

• A decrease in coagulation factors

• An increase in coagulation factors

Answer explanation

Thrombocytosis refers to a condition where there is an increase in circulating platelets in the blood. This is not to be confused with a decrease in circulating platelets or changes in coagulation factors. The correct answer to the question is therefore 'An increase in circulating platelets'.

Which pathway of coagulation is most commonly involved in clinical conditions?

• Extrinsic pathway

• Intrinsic pathway

• Common pathway

• Both extrinsic and intrinsic pathways

Answer explanation

The intrinsic pathway of coagulation is most commonly involved in clinical conditions. It is initiated by the activation of factor XII (Hageman factor) upon contact with negatively charged surfaces, such as those found in damaged blood vessels. This pathway plays a significant role in various bleeding disorders and is more sensitive to deficiencies or abnormalities in clotting factors compared to the extrinsic pathway.