The microvasculature of bone and especially of bone marrow as studied by scanning electron microscopy of vascular casts - A review

This review discusses the microvasculature of bone marrow and its relationship to that of bone cortex as revealed by the vascular corrosion casting/scanning Electron Microscopy (SEM) method. The bone marrow sinusoids are supplied by arteriolar capillaries arsing from the central marrow artery, and anastomose with each other to form a complicated network. The replicated sinusoids are irregular in shape. Only occasionally were protrusions observed on the surface of the sinusoid casts, which were suggestive of pores in the sinusoidal wall; however we frequently noted indentations in the cast surface which presumably reflected the former sites of red cells protruding from the sinusoidal wall into the sinusoidal lumen. The sinusoids are collected into the central vein and hence to the nutrient vein, except for the juxta-endosteal sinusoids which are drained into the periosteal veins via venules traversing the cortex. The microvessels of the bone cortex are also supplied by arteriolar capillaries from the central artery, and drain into periosteal veins. Thus, the marrow sinusoids and the capillary bed in the cortex are not independent but are partially linked by the venules draining the superficial sinusoids of the marrow to the cortex; these vessels are herein termed portal vessels. The possibility of back flow from the cortex to the marrow sinusoids, particularly to those adjacent to the endosteal region of the cortex is so far not excluded: further studies using a variety of methods will be needed, to conclusively establish the actual blood flow pattern in this particular region.