How are platelets formed?

How are platelets formed?

• A. From mature red blood cells that shed membranes
• B. By fragmentation of white blood cells in the spleen
• C. When cytoplasmic fragments of megakaryocytes pinch off into the circulation as they age
• D. Through division of stem cells in the liver

Answer: (C)

Platelets are produced as cytoplasmic fragments of megakaryocytes in the bone marrow. Megakaryocytes extend long processes into marrow sinusoids, and their cytoplasm fragments off into small, anucleate pieces that enter the bloodstream as platelets. This process, thrombopoiesis, is mainly regulated by thrombopoietin produced by the liver and kidneys. Other ideas—formation from mature red blood cells, fragmentation of white blood cells, or division of stem cells in the liver—don’t describe how platelets are generated, since platelets come from megakaryocyte cytoplasmic fragmentation in the bone marrow.

Platelets are produced as cytoplasmic fragments of megakaryocytes in the bone marrow. Megakaryocytes extend long processes into marrow sinusoids, and their cytoplasm fragments off into small, anucleate pieces that enter the bloodstream as platelets. This process, thrombopoiesis, is mainly regulated by thrombopoietin produced by the liver and kidneys. Other ideas—formation from mature red blood cells, fragmentation of white blood cells, or division of stem cells in the liver—don’t describe how platelets are generated, since platelets come from megakaryocyte cytoplasmic fragmentation in the bone marrow.