hypothalamohypophysial portal system hy·po·thal·a·mo·hy·po·phys·i·al portal system (hī'pō-thāl'ə-mō-hī'pə-fĭz'ē-əl, -zē'-, -hī-pŏf'ĭ-sē'əl)
n.
A system of veins that originate in the hypothalmus and pass through the pituitary gland and into its anterior lobe, where they branch into a capillary bed and convey releasing factors to the anterior lobe.