“Pruning” of sinusoids in adipose marrow. (A) CD34-immunolabeled sinusoids as seen in red and yellow areas of human iliac crest bone marrow. The lumen of sinusoids (arrows) running among hematopoietic areas is patent; the lumen of sinusoids running among adipocytes is virtual. (B) The connection of marrow vascularity to bone and fat. Marrow vascularity communicates with bone vascularity. Marrow adipogenesis involves adventitial stromal cells and is coupled with changes in sinusoid caliber.