Vascular organization in the BM cavity. Within a longitudinal view of the diaphysis, ascending and descending medullary arteries branch out to give rise to radial arteries. As they approach the endosteum, radial arterial branches give rise to progressively smaller arterioles. Along the surface of the endosteum, arteriolar circulation transitions into the honeycomb-like network of sinusoidal microvessels, which then collect into the venous central sinus. Periarteriolar environments harbor specific stromal populations such as nestin-GFP^hi mesenchymal stem cells and are niches for quiescent HSPCs.