The vascular system of bone marrow.

Not only the arterial, but also the low pressure system of the bone marrow can be demonstrated by micro-corrosion casts using resins of low viscosity. Vascular bone specimen are obtained by injection of self-curing resin and through subsequent maceration. The three-dimensional representation of the vascular pattern in bone marrow in the scanning electron microscope (SEM) enriches the interpretation of morphology and function of the low pressure system. The nutrient arteries enter the medullary canal and then progress in a spiral form branching into the metaphysis. The arterioles arise from the smaller arteries, further divide into smaller arterial capillaries which then drain into sinusoids which were conically enlarged. The three-dimensional and often hexagonal arrangement of the vascular framework is very evident. Increasing in width the marrow sinusoids drain into wider veins and lastly into the central venous canal. Apart from these medullary sinusoids, finely calibered thin-walled venous capillaries in a regularly anastomosing network can be found as an indication that the wide medullary sinusoids are to be considered as a functional state of active bone marrow.