Figure 5
Electron micrographs of cells from human embryonic aortic ring outgrowths. a, Primitive mesenchymal cells with dendritic cytoplasmic processes and occasional junctional complexes (arrow) (×3000). b, Mesenchymal outgrowths showing focal longitudinal alignment of mesenchymal cells into cord-like structure (arrows). The cells, connected by junctional complexes (arrowheads), have surrounded a space free of extracellular matrix, which may represent a primitive lumen (asterisks) (×3000). c, Neovessel lined by endothelial cells connected by junctional complexes (arrowheads). The lumen contains cell debris. Endothelial cells rest on a thin and discontinuous basal lamina (arrows) (×3000). d, Neovessel surrounded by discontinuous basal lamina (arrow) and collagen fibrils. The endothelium exhibits prominent pinocytotic activity, junctional complexes, and well-defined luminal/abluminal polarity. The luminal space is marked by an asterisk (×3000).
