Structure and Function of Platelets

A microliter of blood contains 150,000 to 400,000 small, disc-shaped cell fragments called platelets or thrombocytes.

These fragments originate in the bone marrow from the myeloid stem cell, which forms the megakaryoblast.

Hormones like thrombopoietin and interleukin-6 influence the megakaryoblast to enlarge and replicate its DNA without cell division, producing megakaryocytes.

These large cells extend multiple cytoplasmic extensions through the sinusoid wall — specialized red marrow capillaries.

As the ends of the extensions rupture, a large number of cell fragments are released into the bloodstream.

These fragments quickly seal their membranes, packaging the cytoplasm into platelets with a 2-4 micrometer diameter.

Platelets lack a nucleus but possess cytoplasmic granules containing clotting factors, enzymes, and growth factors crucial for clotting and wound healing.

When any blood vessel is damaged, platelets rush to the injury site. Their granules release enzymes and growth factors to initiate the clotting process.

They adhere to the damaged walls, forming a temporary plug to prevent further blood loss.