Practice question

Adult tissues with turnover retain resident stem cells in specialized microenvironments. Brain harbors neural stem cells in subventricular zone and hippocampal dentate gyrus, muscle contains satellite cells beneath basal lamina, liver possesses oval cells and facultative progenitors for regeneration. Mature red blood cells are terminally differentiated, enucleated, anucleate biconcave discs lacking DNA, ribosomes, and proliferative capacity. They cannot divide or act as stem cells and are themselves products of hematopoietic stem cells. Their short lifespan of about 120 days requires continuous replacement from bone marrow, not intrinsic self-renewal within circulation.