Superior and inferior hypophyseal arteries (slender branches from arteries of the circle of Willis) that provide blood to the pituitary gland and adjacent regions of the hypothalamus. Venous blood from the pituitary gland drains into the cavernous sinuses and, from there, into the internal jugular veins. Some of the superior hypophyseal arteries form primary capillary beds in the hypothalamus and the veins draining those beds ramify again to form secondary capillary beds in the adenohypophysis (anterior lobe of the pituitary), thus forming a portal circulation (the hypothalamic-pituitary portal circulation). Releasing factors secreted from the hypothalamus into the primary capillary beds reach the adenohypophysis via the secondary capillary beds.