An electron microscope study of elastic tissue

Abstract

Histological elastic tissue from the aorta, renal artery, skin, ligamentum flavum, epiglottis, pinna and vocal cords of man at various ages has been examined in the electron microscope. The aorta of the rabbit and the ligamentum nuchae of the sheep and goat have also been inspected. The elastica has been studied in thin sections of the whole tissue and also in the isolated state. From all sites, in both man and animal, elastic tissue has presented the same characteristic appearance in the electron microscope. The elastica was homogeneous and of low density except for the surface zone. There were neither longitudinal nor cross-striations. There was no evidence of a two-component system of elementary fibrils and amorphous cement substance within the elastic fibres. Wide-angle X-ray diffraction studies of elastic tissue isolated from human aortas of various ages, human ligamentum flavum and sheep ligamentum nuchae gave the same picture—two fairly broad haloes at 4.6 and 7.8 Å. The stretching of the sheep ligamentum nuchae by 100 and 150% did not cause crystallization to occur. The X-ray diffraction patterns of elastic tissue were quite unlike those of collagen. These findings agreed with the appearance of elastic tissue as seen with the electron microscope and with its recognized mechanical properties. The elastic tissue was arranged in the form of networks composed of branching and anastomosing fibres. The network was either loose as in connective tissue, or dense as in the aorta. In the aorta the marked degree of branching and anastomosis reached its highest expression in the fenestrated membranes and sheets of elastica. The fibres varied consider­ably in diameter. The network arrangement was repeated at the level of magnification of the light microscope.