The median eminence is generally defined as the portion of the ventral

hypothalamus The hypothalamus (: hypothalami; ) is a small part of the vertebrate brain that contains a number of nucleus (neuroanatomy), nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrin ...

from which the portal vessels arise. The median eminence is a small swelling on the tuber cinereum, posterior to and on top of the

pituitary stalk The pituitary stalk, also known as the infundibular stalk, infundibulum, or Fenderson's funnel, is the connection between the hypothalamus and the posterior pituitary, the posterior lobe of the pituitary gland. The floor of the third ventricle is ...

; 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 blood–brain barrier (BBB) is a highly selective semipermeable membrane, semipermeable border of endothelium, endothelial cells that regulates the transfer of solutes and chemicals between the circulatory system and the central nervous system ...

, the median eminence is a circumventricular organ having permeable

capillaries A capillary is a small blood vessel, from 5 to 10 micrometres in diameter, and is part of the microcirculation system. Capillaries are microvessels and the smallest blood vessels in the body. They are composed of only the tunica intima (the in ...

. Its main function is as a gateway for release of hypothalamic

hormone A hormone (from the Ancient Greek, Greek participle , "setting in motion") is a class of cell signaling, signaling molecules in multicellular organisms that are sent to distant organs or tissues by complex biological processes to regulate physio ...

s, although it does share contiguous

perivascular space A perivascular space, also known as a Virchow–Robin space, is a fluid-filled space surrounding certain blood vessels in several organs, including the brain, potentially having an immune system, immunological function, but more broadly a dis ...

s with the adjacent hypothalamic

arcuate nucleus The arcuate nucleus of the hypothalamus (ARH), or ARC, is also known as the infundibular nucleus to distinguish it from the arcuate nucleus of the medulla oblongata in the brainstem. The arcuate nucleus is an aggregation of neurons in the medio ...

, indicating a potential sensory role. __TOC__

Physiology

The median eminence is a part of the

from which regulatory hormones are released. It is integral to the

hypophyseal portal system The hypophyseal portal system is a system of blood vessels in the microcirculation at the base of the brain, connecting the hypothalamus with the anterior pituitary. Its main function is to quickly transport and exchange hormones between the hyp ...

, which connects the

with the

pituitary gland The pituitary gland or hypophysis is an endocrine gland in vertebrates. In humans, the pituitary gland is located at the base of the human brain, brain, protruding off the bottom of the hypothalamus. The pituitary gland and the hypothalamus contr ...

. The pars nervosa (part of the posterior pituitary gland) is continuous with the median eminence via the infundibular stalk. Parvocellular neurosecretory cells from the hypothalamus terminate in the median eminence. The median eminence is the structure where secretions of the hypothalamus (

releasing and inhibiting hormones Releasing hormones and inhibiting hormones are hormones whose main purpose is to control the release of other hormones, either by stimulating or inhibiting their release. They are also called liberins () and statins () (respectively), or releasing ...

) regulatory hormones, known as "hypophysiotropic hormones") collect before entering the portal system emptying into the general circulation. Such hypophysiotropic hormones include: CRF ( corticotropin-releasing factor), GnRH (

gonadotropin-releasing hormone Gonadotropin-releasing hormone (GnRH) is a releasing hormone responsible for the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the anterior pituitary. GnRH is a tropic peptide hormone synthesized and rele ...

), TRH (

thyrotropin-releasing hormone Thyrotropin-releasing hormone (TRH) is a hypophysiotropic hormone produced by neurons in the hypothalamus that stimulates the release of thyroid-stimulating hormone (TSH) as well as prolactin from the anterior pituitary. TRH has been used ...

), GHRH (

growth hormone-releasing hormone Growth may refer to: Biology * Auxology, the study of all aspects of human physical growth * Bacterial growth *Cell growth *Growth hormone, a peptide hormone that stimulates growth *Human development (biology) *Plant growth *Secondary growth, gro ...

), and DA (

dopamine Dopamine (DA, a contraction of 3,4-dihydroxyphenethylamine) is a neuromodulatory molecule that plays several important roles in cells. It is an organic chemical of the catecholamine and phenethylamine families. It is an amine synthesized ...

). These hypophysiotropic hormones stimulate or inhibit the release of hormones from the

anterior pituitary The anterior pituitary (also called the adenohypophysis or pars anterior) is a major Organ (anatomy), organ of the endocrine system. The anterior pituitary is the glandular, Anatomical terms of location#Usage in human anatomy, anterior lobe that t ...

. Further, anatomical evidence exists for bidirectional communication between the median eminence and the arcuate and ventromedial nucleus of the hypothalamus.

References

{{Authority control Endocrine system anatomy Neuroendocrinology Hypothalamus