THE VASCULAR SYSTEM OF HUMAN FETAL LONG BONES - A SCANNING ELECTRON-MICROSCOPE STUDY OF CORROSION CASTS

The vascular system of the femur and humerus was investigated in 17-24 wk human fetuses by scanning electron microscopy of corrosion casts. The number of nutrient foramina present in both bones ranged from 1 to 3 and the number of nutrient vessels associated with individual foram ina also varied. The medullary arteries supplied both the bone cortex and marrow. There was no arterial supply to the shaft cortex from the periosteal side, where only capillaries were found to enter the bone. The metaphyses were supplied and drained by conspicuous vascular triad s composed of an artery and 2 veins. In the marrow cavity, 2 morpholog ically different areas of the fine vascular network could be distingui shed: diaphyseal sinusoids and metaphyseal capillaries forming a 'vasc ular besom' which was abruptly demarcated by the growth plate cartilag e. The cortical microvascular bed was composed of capillaries and more numerous irregular sinusoids. The 2 main vascular systems, nutrient a nd periosteal, were interconnected not only via the network of cortica l capillaries/sinusoids, but also by larger arteries and veins travers ing the cortex. The features of the vascular system of human fetal lon g bones suggest its considerable functional flexibility and its capaci ty to modify blood flow patterns depending on circumstances.