Megakaryocytes

Megakaryocyte
Two megakaryocytes in bone marrow, marked with arrows.
Details
Identifiers
Latin	megakaryocytus
Code	TH H2.00.04.3.05003
Anatomical terminology []

A megakaryocyte ( + + , "large-nucleus cell") 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. Megakaryocytes normally account for 1 out of 10,000 bone marrow cells but can increase in number nearly 10-fold during the course of certain diseases. Owing to variations in combining forms and spelling, synonyms include megalokaryocyte and megacaryocyte.

In general, megakaryocytes are 10 to 15 times larger than a typical red blood cell, averaging 50-100 μm in diameter. During its maturation, the megakaryocyte grows in size and replicates its DNA without cytokinesis in a process called endomitosis. As a result, the nucleus of the megakaryocyte can become very large and lobulated, which, under a light microscope, can give the false impression that there are several nuclei. In some cases, the nucleus may contain up to 64N DNA, or 32 copies of the normal complement of DNA in a human cell.

The cytoplasm, just as the platelets that bud off from it, contains α-granula and Dense bodies.

Megakaryocytes are derived from hematopoietic stem cell precursor cells in the bone marrow. They are produced primarily by the liver, kidney, spleen, and bone marrow. These multipotent stem cells live in the marrow sinusoids and are capable of producing all types of blood cells depending on the signals they receive. The primary signal for megakaryocyte production is thrombopoietin or TPO. TPO is sufficient but not absolutely necessary for inducing differentiation of progenitor cells in the bone marrow towards a final megakaryocyte phenotype. Other molecular signals for megakaryocyte differentiation include GM-CSF, IL-3, IL-6, IL-11, chemokines (SDF-1, FGF-4). and erythropoietin. The megakaryocyte develops through the following lineage: