This chapter discusses the development of hypothalamic-hypophysial vasculature and its relationship to secretory cells of the hypothalamus and pituitary gland. The sinusoids of the pars distalis of the pituitary gland and the capillaries in the floor of the ventricular recess of the third ventricle are connected through veins that lie on the surface of the pituitary stalk. The venous drainage of the neurohypophysis, by way of veins, connects the pars neuralis with the cavernous sinus and by way of portal vessels connects the median eminence and pituitary stalk with the pars distalis. The pars distalis of the adenohypophysis receives only venous blood by way of hypophysial portal vessels. The primary capillary plexus of the portal vessels lies in the median eminence and pituitary stalk; the secondary capillary plexus of these vessels lies in the pars distalis. Neurosecretory cells, lying within diffusion distances of the primary capillary plexus of the portal vessels, secrete products that diffuse into the blood of the portal vessels. Some pituitary hormones act on neurons of the hypothalamus to alter their activity.
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