Question

When body tissues are injured resulting in the loss of blood, the process of blood clot begins and the blood platelets release:
A. Prothrombin
B. Thrombin
C. Fibrinogen
D. Thromboplastin

Answer 1

Blood clotting, also called coagulation, is an important process that prevents excessive bleeding when a blood vessel is injured. Platelets, which is a type of blood cell and proteins in plasma, which is the liquid part of blood, work together in order to stop the bleeding by forming a clot over the injury.

Complete answer:
There are three steps to the process of blood clotting which are vascular spasm, the formation of a platelet plug, and coagulation which is blood clotting. Failure of any of these steps will result in hemorrhage which means excessive bleeding.
Prothrombin is a protein which is made by the liver. It is one of several substances which are known as clotting or coagulation factors. Therefore, prothrombin is not released by platelets.
Thrombin is a naturally occurring enzyme which is responsible for converting fibrinogen into fibrin, which is an integral step in the process of clot formation. Thrombin is formed from prothrombin due to the activation of both the intrinsic and extrinsic pathways of the coagulation cascade. Hence, it is not released by the blood platelets.
Fibrinogen, or factor one, is a blood plasma protein that is made in the liver. Fibrinogen is one of the thirteen coagulation factors that is responsible for normal blood clotting and is not released by blood platelets.
Thromboplastin is released by blood platelets during an injury, it then converts the plasma protein prothrombin into thrombin which then converts fibrinogen into fibrin which forms a meshwork by trapping red blood cells, thereby forming a clot.

Therefore, the correct answer is option D.

Note:
The coagulation pathway is a cascade of events which leads to hemostasis. There is an intrinsic and extrinsic pathway. Intrinsic pathway helps in rapid healing and also prevents spontaneous bleeding. Both the pathways originate separately but they meet at a specific common point which leads to fibrin activation.