[Structural changes of fenestrated capillaries during development of various endocrine glands in the chicken].

The ultrastructure of the blood capillaries has been analyzed in the adenohypophysis, the pineal body, the thyroid and the suprarenal gland of chick embryos of 7, 14 and 19 days of incubation and, respectively, of the adult fowl. During the organogenesis of these endocrine glands the vascular primordia, precociously appearing among the epithelial components, undergo morphological maturative changes leading to the formation of capillaries built of a fenestrated endothelium and an underlying thin layer of pericytes included in a splitting of the endothelial basement lamina. The capillary differentiation processes, almost identical in the mentioned glands, follow a different chronological sequence, occurring precociously in thyroid and suprarenal and later on in adenohypophysis and pineal body. The relationships between the structural modifications of the capillary wall and the morphological and functional differentiation of the endocrine cells during the organogenesis of the glands have been briefly discussed.