20880D

20880D
Caption: Photocomposite - Hematopoietic human stem cells (adult) in the bone marrow cavity (mammal). For illustrative purposes the human borrow marrow cells have been enlarged and placed in a mammal's bone marrow cavity.
Stem cells are part of the hematopoietic / reticuloendothelial system and give rise to specialized blood cells (macrophages, histiocytes). This is the macrophage system that includes all histiocytes, macrophages, reticular cells, monocytes and microglia. It does not include the granular white blood cells (granulocytes). The bone marrow consists of packed hematopoietic cells, reticular cells and adipose cells. They occupy all the extravascular spaces around an extensive system of channels called venous sinuses. Blood cells develop outside of the extravascular system and must pass through the walls of the sinuses to enter the circulation system. The renewal of all types of blood cells is necessitated by their relatively short lifespan. The common stem cells developing in bone marrow differentiate along various lines to form red and white blood cells (granular leukocytes or monocytes). Active or red marrow is dominated by the production of red blood cells. With increasing age the marrow becomes less active and is progressively inhabited by adipocytes (fat cells). Osteocyte cell bodies also reside in other smaller cavities (lacunae) of the surrounding compact bone.
Magnification*: x70(cavity x290(stem)
Type: SEM
Copyright 2000 Dennis Kunkel Microscopy, Inc.
Keywords: 20880D,human body,blood,human stem cell,hematopoietic stem cell,bone marrow,hematopoietic system,reticuloendothelial system,macrophage system,histiocyte,reticular cell,monocyte,microglia,Kupffer cell,bone marrow cavity,lacuna,lacunae,adipose cell,venous sinuses,red blood cell,white blood cell formation,osteocyte cell,SEM,stem cells,compact bone,cortical bone,osteoblast,bone,bone fracture,osteocyte