Ultrastructure of the human pharyngeal hypophysis.

Four types of secretory cells have been distinguished in the human pharyngeal hypophysis. Type I cells contain granules of about 70-90 nm in diameter; type II cells are the most numerous and are loaded with granules ranging in size between 100 and 200 nm. In type III cells the size of the granules ranges between 150 and 250 nm in diameter. Type IV cells contain the largest secretory granules (250-400 nm). In addition, there is a type of cell lacking secretory granules and which has been regarded as interstitial cell (type V). The different cell types are arranged in clusters which, in turn, are surrounded by numerous blood capillaries. A few nerve fibres have been observed within the gland. These fibres make synaptoid contacts with type II cells. The ultrastructural analysis of the human phayngeal hypophysis strongly suggests that this formation is an endocrine gland with distinct characteristics and with a functional role probably different from that of the sellar hypophysis.