Ultrastructural features of the vasculogenetic processes in the thyroid and suprarenal glands of the chick embryo.

This paper reports the results of an ultrastructural investigation on the differentiation of the blood capillary network in the thyroid and suprarenal glands of the chick embryo, from the 6th to the 21st incubation day. Apart from some morphological features of the capillary wall, which change in the same way during gland organogenesis (thickness of the endothelium, quantity and distribution of cytoplasmic organelles, pores), differences have been pointed out concerning the beginning and temporal evolution of the maturative events of the endothelium lining and the pericapillary spaces. Close relationships between morphofunctional maturation of the secretory cells and blood vessel differentiation have been emphasized, and the roles played by intraendothelial vacuoles and endothelial basement lamina during the capillarogenesis are discussed.