Human Immunity and Blood

Thromboplastin (also known as tissue factor) is released by damaged tissues and also produced by blood platelets to initiate the extrinsic and intrinsic pathways of blood coagulation.

Blood platelets (thrombocytes) are essential for hemostasis and release thromboplastin when they aggregate at a site of injury.

Thrombocytes (platelets) have a relatively short lifespan in the circulation, typically ranging from 5 to 9 days before being cleared by the spleen.

Thrombocytopenia is a medical condition characterized by a low blood platelet count, which often requires platelet transfusions.

Megakaryocytes are large bone marrow cells that fragment into smaller pieces called platelets or thrombocytes. These fragments are essential for the blood clotting process.

According to the classic physiology text by Best and Taylor, platelets are considered to be involved in the formation of the platelet plug, but they are distinct from the chemical clotting factors like fibrinogen, prothrombin, and calcium that form the fibrin mesh.

Thrombocytes, commonly known as platelets, are the blood cells primarily responsible for initiating the blood clotting process to prevent excessive bleeding.

When a blood vessel is injured, blood platelets aggregate at the site and release thromboplastin, which initiates the extrinsic pathway of the blood clotting cascade.

Thrombocytes (platelets) are essential for blood coagulation. A deficiency in their number, known as thrombocytopenia, impairs the clotting mechanism and can lead to excessive bleeding.

Thrombocytes are also called Platelets. They are the vital component of blood. It's basic function is to stop bleeding by clumping and clotting blood vessel injuries. Its main function is to contribute to hemostasis that is the process of stop bleeding by adhesion. Reduction in the number of platelets causes clotting disorder and thus loss of blood from the body.

Monocytes are actively phagocytic and they take in the invading pathogen or cell through the method of phagocytosis.

Platelets are formed by the fragmentation of special cells named megakaryocytes in bone marrow cell so answer is option.        

A megakaryocyte is a large bone marrow cell with a lobulated nucleus, responsible for the production of blood thrombocytes (platelets), which are necessary for normal blood clotting. 

Critical count of platelet is 40, 000 / mm$^{3}$. Platelets, also called thrombocytes, are blood cells whose function is to stop bleeding. Platelets have no nucleus: they are fragments of cytoplasm, which are derived from the megakaryocytes of the bone marrow, and then enter the circulation. These unactivated platelets are biconvex discoid structures. The normal number of platelets in the blood is 150,000 - 400,000 platelets per microliter (mcL). A low platelet count is below 150,000. If the platelet count is below 50,000, the risk of bleeding is very high. So, it is called critical platelet count.

Platelets are the cells found in blood which helps in the clotting of the blood. The formation of platelets takes place in bone marrow from large bone marrow cells known as megakaryocytes. These cells after becoming mature enough, undergo the process of cell fragmentation to produce platelet cells. The hormone that help in platelet production is thrombopoietin.