A Study on the Development of the Thoracic Aorta in Human Fetus / 체질인류학회지

ABSTRACT

Prenatal development of the thoracic aorta of the human during the period ranging from gestation weeks 7 (C-R length 20mm) to 30 (C-R length 260mm) was examined by transmission electron microscopy and the following results were obtained. The early form of cuboidal or columnar endothelial cells at 7-9 weeks of gestation changed gradually to typical flat endothelial cells at 12-14 weeks of gestation. At 9 weeks of gestation, the mesenchymal cells begin to differentiate to myoblasts, which have small clusters of myofilaments with dense bodies and rough endoplasmic reticulum. And from 14 weeks the differentiating cells begin to form a parallel concentric lamellar structure. At 12th week of gestation, elastic fibers were first seen in subendothelial connective tissue and the intercellular spaces between smooth muscle cells. Elastic fibers appeared as small globular shape which composed of a central core of elastic and peripheral microfibrils. From this period the amount of elastic fibers and their aggregation increases gradually in both the subendothelial space and the intercellular spaces between smooth muscle cells. At 30th week of gestation, subendothelial elastic fibers almost completed the internal elastic lamina and also well formed elastic laminae were seen between the smooth muscle cells adjacent to endothelial cells. However, in the space between the smooth muscle cells near the adventitia the elastic lamina formation is delayed. In the adventitia elastic fiber were scanty but collagen fibers are abundant.