Fig. 20. Electron micrograph of the external zone of the median eminence showing the presence of axon terminals (a) and a tanycyte process (t) adjacent to a fenestrated capillary (C) of the portal plexus. One axon (closed arrowhead) has been engulfed by the tanycyte and another (open arrowhead) is separated from the portal capillary space by the tanycyte foot process. Note presence of dense core vesicles (arrows) as well as smaller secretory vesicles in several axon terminals. (From Lechan RM, Functional Microanatomy of the Hypophysial-Pituitary Axis, in Melmed, S (Ed), Oncogenesis and Molecular Biology of Pituitary Tumors, Frontiers of Hormone Research, 20: 2-40, 1996.)