Corpus: Median eminence

The eminentia mediana is a highly vascularised region in the area of the pituitary stalk at the base of the hypothalamus, which plays an important role in the release of the so-called regulatory hormones.

The eminentia mediana is surrounded posterolaterally by the pedunculi cerebri and anterolaterally by the optic chiasm. It lies at the base of the 3rd cerebral ventricle and is part of the infundibulum. The tissue area is one of the neurohemal regions in which the blood-brain barrier is lifted.

Histologically, the eminentia mediana can be divided into three zones:

• inner ependymal zone, near the 3rd ventricle
• inner pallisade zone
• outer pallisade zone

The middle, "inner" pallisade zone contains medullary neurones that run to the posterior lobe of the pituitary gland (HHL). Specialised capillary loops protrude in the outer pallisade zone. The axons of nerve cells whose subependymal scattered cell bodies lie in the periventricular space of the hypothalamus end between them. They can be demarcated as separate nuclear areas in the periventricular nucleus and the infundibular nucleus. The contact between the 3rd ventricle and the outer pallisade zone is mediated by specially differentiated ependymal cells, the so-called tanycytes.

The axons of these nerve cells release neuropeptides into the blood via special contact structures, the neurovascular junctions. They reach the adenohypophysis via the pituitary-portal vein system, where they act as releasing factors (liberins) or inhibiting factors (statins). This makes the eminentia mediana the most important interface between the nervous and endocrine systems.