The structure and vascularization of the pars tuberalis of the hypophysis of Rana temporaria

Summary The pars tuberalis of the hypophysis of Rana temporaria presents the general structural and the cytological characteristics of an endocrine gland. It is composed of elongated cells with long, branching processes ending on the external basement membrane of the pericapillary space. The pars tuberalis cells produce secretory granules which are accumulated in the pericapillary endings of the processes.Corresponding to its separate localization, the pars tuberalis of Rana temporaria has a separate vascularization of which the efferent capillaries anastomose with the capillary plexus of the median eminence. The general direction of the blood flow of the pars tuberalis is towards the capillaries of the median eminence. Also, the secretory products of the pars tuberalis pass into the blood stream of the hypophysial portal system.Several characteristics of the pars tuberalis show that its function must be different from that of the pars distalis of the hypophysis. Moreover, in contrast with the pars distalis, the activity of the pars tuberalis is not regulated by neurohumoral factors.The results show that a role of the pars tuberalis in the regulation of the activity of the pars distalis of the hypophysis is not excluded.