In the hematopoietic system, a small number of stem cells produce a progeny of several distinct lineages. During ontogeny, they arise in the aorta-gonad-mesonephros region of the embryo and the placenta, afterwards colonise the liver and finally the bone marrow. After this fetal phase of rapid expansion, the number of hematopoietic stem cells continues to grow, in order to sustain the increasing blood volume of the developing newborn, and eventually reaches a steady-state. The kinetics of this growth are mirrored by the rates of telomere shortening in leukocytes. During adulthood, hematopoietic stem cells undergo a very small number of cell divisions. Nonetheless, they are subjected to aging, eventually reducing their potential to produce differentiated progeny. The causal relationships between telomere shortening, DNA damage, epigenetic changes, and aging have still to be elucidated.

中文翻译：

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造血干细胞的生长和老化。

在造血系统中，少量干细胞产生几个不同谱系的后代。在个体发育过程中，它们出现在胚胎和胎盘的主动脉-性腺-中肾区域，然后定植于肝脏，最后定植于骨髓。在这个快速扩张的胎儿期之后，造血干细胞的数量继续增长，以维持正在发育的新生儿不断增加的血容量，并最终达到稳定状态。白细胞中端粒缩短的速率反映了这种生长的动力学。在成年期，造血干细胞会进行极少量的细胞分裂。尽管如此，它们会老化，最终降低它们产生分化后代的潜力。端粒缩短、DNA 损伤、表观遗传变化之间的因果关系，