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A megakaryocyte (from mega- 'large' karyo- 'cell nucleus' and -cyte 'cell') is a large bone marrow cell with a lobated nucleus that produces blood platelets (thrombocytes), which are necessary for normal clotting. In humans, megakaryocytes usually account for 1 out of 10,000 bone marrow cells, but can increase in number nearly 10-fold during ...
Compared to megakaryoblasts, promegakaryocytes and granular megakaryocytes are both larger and contain less basophilic cytoplasm with granules. Promegakaryocytes are usually about 15μm to 30μm in diameter with a lobed nucleus and some azurophil granules within moderately basophilic cytoplasm.
Megakaryocytes are precursor cells that are highly specialized. Megakaryocytes give rise to 1,000 to 3,000 platelets. Megakaryocytes function in the process of Thrombopoiesis by producing platelets and releasing platelets into the bloodstream. [6] Megakaryocyte development is regulated mainly by thrombopoietin.
Low platelets and megakaryocytes lead a higher degree of thrombopoietin exposure to the undifferentiated bone marrow cells, leading to differentiation into megakaryocytes and further maturation of these cells. On the other hand, high platelet and megakaryocyte concentrations lead to more thrombopoetin destruction and thus less availability of ...
Red blood cells are much smaller than most other human cells. RBCs are formed in the red bone marrow from hematopoietic stem cells in a process known as erythropoiesis. In adults, about 2.4 million RBCs are produced each second. The normal RBCs count is 4.5 to 5 millions per cu.mm. RBCs have a lifespan of approximately 100-120 days.
It is composed of 270 bones at the time of birth, [2] but later decreases to 206: 80 bones in the axial skeleton and 126 bones in the appendicular skeleton. 172 of 206 bones are part of a pair and the remaining 34 are unpaired. [3] Many small accessory bones, such as sesamoid bones, are not included in this.
The bones were determined to be up to 47,500 years old. Until now, the oldest Homo sapiens remains from northern central and northwestern Europe were about 40,000 years old.
The human pelvis exhibits greater sexual dimorphism than other bones, specifically in the size and shape of the pelvic cavity, ilia, greater sciatic notches, and the sub-pubic angle. The Phenice method is commonly used to determine the sex of an unidentified human skeleton by anthropologists with 96% to 100% accuracy in some populations.