Fig. 1.

Blood vessel formation and function in the bone tissue. a Vasculogenesis and angiogenesis. Two distinct mechanisms of blood vessel formation. Vasculogenesis gives rise to the primitive vascular plexus during embryogenesis. Stimulated by tumors and hypoxic conditions, angiogenesis remodels and expands the vascular network. Reproduced with permission [33].

Copyright 2012, American Association for the Advancement of Science. b Perivascular cells associated with blood vessels in the bone. Larger arteries are covered by smooth muscle cells that are connected to the H capillaries while mesenchymal cells are found on sinusoidal type L-vessels. c Illustration of intramembranous angiogenesis. Mesenchymal cells condense to form sponge-like structures and differentiate into osteoprogenitors and osteoblasts. Matrix proteins and pro-angiogenic factors generated by the ossification centers then attract blood vessels. b and c are reproduced with permission [48]. Copyright 2016, The Company of Biologists Ltd