As circumventricular organs a number of different organs is referred to in the brain to the III. and IV. cerebral ventricles are located and represent special formations of the ventricular wall. They lie as unpaired structures in the median level of the brain and carry various functions, some of which are not yet fully understood.
Common structural features of these organs can be found not only in the conspicuous position and arrangement as macroscopic characteristics, but also in the anatomical structure of the tissue. These peculiarities are related to their special location at the interface of fluid spaces that are otherwise separated by the so-called blood-brain barrier . In contrast to the other brain structures, the blood vessels of most circumventricular organs are only separated from the brain tissue by a fenestrated (fenestrated) endothelium , which allows the transfer of higher molecular substances from the blood to the brain and vice versa (see neurohemal organs ). The organum subcommissurale with its non-fenestrated capillary endothelium is an exception . Various glycoproteins are formed in the subcommissural organ and secreted into the liquor space.
A layer of specialized ependymal cells ( tanycytes ), which form the wall of the latter , is usually found facing the ventricular space leading to the liquor . Under this layer of the ependyma lies a specific zone of subependymal tissue with neurons. In several of the circumventricular organs, these produce, among other things, neurohormones that are released into the blood.
In regions of the area postrema of the brain stem there are also nerve cells that are sensitive to substances that have leaked from the liquor. In contrast , the vascular organ of the lamina terminalis , which is located rostrally near the optic chiasm, contains, among other things, cells that react to pyrogenic substances in the blood, while those in the subfornical organ are sensitive to angiotensin . In the median eminentia of the pituitary stalk , hormones such as somatostatin and gonadoliberin are released by neurons that act on target cells in the adenohypophysis . In contrast to this, the neurohypophysis is one of the circumventricular organs and, as a neurohemal organ, releases the hormones oxytocin and vasopressin (ADH) into the bloodstream.
- Area postrema (part of the vomiting center in the brain stem )
- Organum subfornicale (Subfornikalorgan, SFO)
- Organum vasculosum laminae terminalis (OVLT)
- Eminentia mediana of the pituitary stalk
- Neurohypophysis (posterior pituitary gland, HHL)
also both the Epithalamus associated
- H. M. Duvernoy, PY Risold: The circumventricular organs: an atlas of comparative anatomy and vascularization. In: Brain Res Rev 56, 2007, pp. 119-147. PMID 17659349 (Review).