Question

Chemicals released by blood platelets is
A. Heparin
B. Thromboplastin
C. Fibrinogen
D. Prothrombin

Answer 1

Hint: A platelet, also called a thrombocyte, is a colourless, non-nucleated portion of the blood that is essential for blood clot formation (coagulation). Only in the blood of mammals are platelets present.

Complete Answer:
- As cytoplasmic fragments of megakaryocytes, which are very large cells in the bone marrow, are pinched off into the circulation as they mature, platelets are formed. Stored in the spleen, they are in the formation of a blood clot, platelets play an important role by aggregating to block a cut blood vessel and providing a surface on which fibrin strands form an organised clot, by contracting to force the fibrin strands together to make the clot strong and lasting and perhaps most importantly, by providing or mediating a variety of clotting factors required for the clot to form.
- Several hormones, including serotonin, epinephrine, histamine, and thromboxane, are often processed and transported by platelets; upon activation, these molecules are released and local blood vessel constriction is triggered, promoting clot formation.
- Thromboplastin is a plasma protein supporting blood coagulation by catalysing the conversion of prothrombin to thrombin. It is a complex enzyme found in the brain, lungs and other tissues, particularly platelets in the blood.
- The mast cells and blood basophils produce heparin. A hepatic parenchymal cell is formed by fibrinogen. It is transformed into fibrin by thrombin during the formation of blood clots. In the parenchymal cells of the liver, prothrombin is stored.

The correct Answer is option (B) Thromboplastin.

Note: At birth, the number of platelets is small, but the adult amount is reached by the age of three months. After trauma or asphyxiation, the number of platelets increases at high altitudes, after exercise, and at cold temperatures; the number may be temporarily lowered in women due to menstruation. The life of platelets can be extended by certain chemicals; smoking is believed to shorten their life spans.