in lampreys and teleost hormones enter the adenohypophysis by diffusion.

One of the most important functions of the hypothalamus is to link the nervous system to the endocrine system via the pituitary gland (hypophysis). The hypothalamus is responsible for certain metabolic processes and other activities of the autonomic nervous system. It synthesizes and secretes certain neurohormones, often called hypothalamic-releasing hormones, and these in turn stimulate or inhibit the secretion of pituitary hormones. The hypothalamus controls body temperature, hunger, thirst, fatigue, sleep, and circadian cycles

we represent this structure strictly as a system of blood vessels (presumably in line with the FMA). It could also be extended to include neurons and fiber tracts, as per the MESH definition

hypothalamo-hypophyseal system, set of portal veins of hypophysis, hypothalamo hypophyseal system, venae portales hypophysiales, portal veins of hypophysis

uberon

UBERON:0009976

http://purl.obolibrary.org/obo/NCBITaxon_32443

Set of portal veins of hypophysis