NationMaster - Encyclopedia: Megakaryocyte

The megakaryocyte is a bone marrow cell responsible for the production of blood platelets when its cytoplasm becomes fragmented. These fragments are blood platelets. Megakaryocytes account for less than 1% of bone marrow cells but can be 10 to 15 times larger than a typical red blood cell.(Compare to other cells) DNA synthesis is occuring in the nucleus during thrombopoiesis (stimulated by thrombopoietin) without cytokenesis, aka endoreduplication. Therefore, 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 o 64N DNA. Grays Anatomy illustration of cells in bone marrow. ... Cells in culture, stained for keratin (red) and DNA (green). ... A 250 ml bag of newly collected platelets. ...

Platelets are held within demarcation channels, internal membranes within the cytoplasm of megakaryocytes. Megakaryocytes release their platelets in one of two ways. The cell may release its platelets by rupturing and releasing its contents all at once in the marrow. Alternatively, the cell may form platelet ribbons into blood vessels. The ribbons are formed via psuedopodia and they are able to continuously emit platelets into circulation. 2/3 of these platelets will remain in circulation while 1/3 will be sequestered by the spleen.

Megakaryocyte function is determined by a large number of cytokines, including thrombopoietin. Cytokines is a group of proteinaceous signalling compounds that like hormones and neurotransmitters are used extensively for inter-cell communication. ... Thrombopoietin is the recently discovered (1994) glycoprotein hormone that regulates the production of platelets. ...

The developmental stages of the megakaryocyte is: CFU-Me (pluripotential hemopoietic stem cell or hemocytoblast) -> megakaryoblast -> promegakaryocyte -> megakaryocyte. Sketch of bone marrow and its cells Pluripotential hemopoietic stem cells or pluripotential hematopoietic stem cells (PHSCs) are stem cells found in the bone marrow. ... A megakaryoblast is a precursor cell to a promegakaryocyte, which in turn becomes a megakaryocyte. ...

Categories: Immunology stubs | Blood and immune system cells Human blood smear: a - erythrocytes; b - neutrophil; c - eosinophil; d - lymphocyte. ... Blood plasma is the liquid component of blood, in which the blood cells are suspended. ... Sketch of bone marrow and its cells Pluripotential hemopoietic stem cells or pluripotential hematopoietic stem cells (PHSCs) are stem cells found in the bone marrow. ... Human red blood cells Red blood cells are the most common type of blood cell and are the vertebrate bodys principal means of delivering oxygen from the lungs or gills to body tissues via the blood. ... Reticulocytes are immature red blood cells, that normally comprise about 1% of the red cells in the human body. ... A normoblast (or erythroblast) is a type of red blood cell which still retains a cell nucleus. ... White blood cells (a. ... A lymphocyte is a type of white blood cell involved in the human bodys immune system. ... Lymphoblasts are interferons produced predominantly by leucocyte cells. ... T cells are a subset of lymphocytes that play a large role in the immune response. ... A cytotoxic (or TC) T cell is a T cell (a type of white blood cell) which has on its surface antigen receptors called T-cell receptors (TCRs) that can bind to fragments of antigens displayed by the Class I MHC molecules of virus (or other intracellular pathogen) infected somatic... T helper cells (also known as effector T cells or Th cells) are a sub-group of lymphocytes (a type of white blood cell or leukocyte) that play an important role in establishing and maximising the capabilities of the immune system. ... Regulatory T cells (also known as suppressor T cells) are a specialized subpopulation of T cells that act to suppress activation of the immune system and thereby maintain immune system homeostasis and tolerance to self. ... Natural killer T cells (NK T cells) are a type of lymphocyte, or white blood cell. ... B cells are lymphocytes that play a large role in the humoral immune response (as opposed to the cell-mediated immune response). ... Plasma cells (also called plasma B cells or plasmocytes) are cells of the immune system that secrete large amounts of antibodies. ... Memory B cells are a B cell sub-type that are formed following primary infection. ... Natural NK cells are cytotoxic; small granules in their cytoplasm contain special proteins such as perforin and proteases known as granzymes. ... Sketch of bone marrow and its cells Pluripotential hemopoietic stem cells or pluripotential hematopoietic stem cells (PHSCs) are stem cells found in the bone marrow. ... Myeloblasts or blasts are new, immature blood cells developed in the bone marrow that are the precursors of myelocytes. ... Granulocytes are a category of white blood cells characterised by the presence of granules in their cytoplasm. ... Neutrophil granulocytes, generally referred to as neutrophils, are the most abundant type of white blood cells and form an integral part of the immune system. ... Eosinophils are white blood cells that are responsible for combating infection by parasites in the body. ... Basophil granulocyte Basophils are the least common of the granulocytes, representing about 1% of circulating leukocytes. ... Mast cells A mast cell (or mastocyte) is a resident cell of connective tissue that contains many granules rich in histamine and heparin. ... Monocyte A monocyte is a leukocyte, part of the human bodys immune system that protect against blood-borne pathogens and move quickly to sites of infection in the tissues. ... A Histiocyte is a cell that is part of the human immune system. ... A macrophage of a mouse stretching its arms to engulf two particles, possibly pathogens Macrophages (Greek: big eaters, makros = long, phagein = eat) are white blood cells, more specifically phagocytes, acting in the nonspecific defense as well as the specific defense system of vertebrate animals. ... Dendritic cells (DC) are immune cells and form part of the mammal immune system. ... Langerhans cells are immature dendritic cells containing large granules called Birbeck granules. ... Microglia are a type of glial cell that act as the immune cells of the Central nervous system (CNS). ... Kupffer cells are reticulendothelial cells located in the liver. ... An osteoclast is a multinucleated cell that degrades and reabsorbs bone. ... A megakaryoblast is a precursor cell to a promegakaryocyte, which in turn becomes a megakaryocyte. ... A 250 ml bag of newly collected platelets. ...