Platelets are cell fragments of large multinucleate cells called __.
A) granulocytes
B) agranulocytes
C) erythrocytes
D) megakaryocytes
The correct answer and explanation is:
The correct answer is D) megakaryocytes.
Platelets, also known as thrombocytes, are small cell fragments involved in blood clotting. They originate from large, multinucleate cells called megakaryocytes, which are found in the bone marrow. These megakaryocytes undergo a unique process where they extend large cytoplasmic projections known as proplatelets into the bloodstream. As the proplatelets break off, they form the small, disc-shaped platelets.
Megakaryocytes are large, bone marrow-derived cells with multiple nuclei due to repeated rounds of DNA replication without cell division. This unique characteristic allows them to produce a large number of platelets. Platelets themselves do not contain nuclei, as they are fragments of the cytoplasm of the megakaryocytes. The primary function of platelets is to assist in blood clotting, which helps prevent excessive bleeding when blood vessels are injured. They adhere to the site of injury, aggregate with other platelets, and release various substances that promote the formation of a fibrin clot, ultimately sealing the wound.
The formation of platelets is regulated by the hormone thrombopoietin, which is produced mainly by the liver. Thrombopoietin stimulates the production and maturation of megakaryocytes, thereby influencing platelet production. The lifespan of platelets in circulation is relatively short, typically around 7 to 10 days, after which they are removed from the bloodstream by macrophages in the spleen and liver.
Understanding the role of megakaryocytes in platelet production is crucial for diagnosing and treating various bleeding disorders, such as thrombocytopenia, where there is an abnormally low platelet count, or thrombocytosis, where there is an abnormally high platelet count.