Median eminence


The median eminence, part of the inferior boundary of the hypothalamus in the brain, is attached to the infundibulum. The median eminence is a small swelling on the tuber cinereum, posterior to and atop the pituitary stalk; it lies in the area roughly bounded on its posterolateral region by the cerebral peduncles, and on its anterolateral region by the optic chiasm.
As one of the seven areas of the brain devoid of a blood–brain barrier, the median eminence is a circumventricular organ having permeable capillaries. Its main function is as a gateway for release of hypothalamic hormones, although it does share contiguous perivascular spaces with the adjacent hypothalamic arcuate nucleus, indicating a potential sensory role.

Physiology

The median eminence is a part of the hypothalamus from which regulatory hormones are released. It is integral to the hypophyseal portal system, which connects the hypothalamus with the pituitary gland. The pars nervosa is continuous with the median eminence of the hypothalamus via the infundibular stalk. Parvocellular neurons from the hypothalamus terminate in the median eminence of the hypothalamus.
The median eminence is the structure where secretions of the hypothalamus collect before entering the portal system emptying into the general circulation. Such hypophysiotropic hormones include: CRF, GnRH, TRH, GHRH, and DA. These hypophysiotropic hormones stimulate or inhibit the release of hormones from the anterior pituitary. Further, anatomical evidence exists for bidirectional communication between the median eminence and the arcuate and ventromedial nucleus of the hypothalamus.