Practice question

Adult stem cells persist postnatally within specialized niches such as bone marrow, intestinal crypts, and hair follicle bulge. Unlike embryonic stem cells that construct the entire organism, these tissue-resident populations maintain homeostasis by replacing short-lived differentiated cells lost to turnover, injury, or mechanical stress. Through balanced self-renewal and lineage commitment governed by Wnt, Notch, BMP and local growth factors, they generate transit-amplifying progenitors that restore epithelia, blood, muscle, and neural lineages, ensuring long-term repair without forming extraembryonic tissues or whole embryos during adulthood.