Subfornical organ

The Organum subfornical or Subfornikalorgan is located on the roof of the III. Ventricle below the fornix (Latin for " vault "). It is one of the circumventricular organs with special fenestriertem ependyma and ependymal cells, the Tanycyten. At this point, the blood- brain barrier is disrupted.

Function

The Organum subfornical is involved in the regulation of salt and water balance of the body. The neurons are particularly sensitive to the hormone angiotensin II, which in case of low blood pressure due to proteolysis by renin and converting by the angiotensin converting enzyme ( ACE) is formed from the zymogen angiotensinogen ( renin -angiotensin system ). This activation of angiotensin II takes place at very low blood pressure. The Organum subfornical sent on the angiotensin II - stimulus signals via efferent fibers in the nucleus of the hypothalamus preopticus. As a transmitter acts angiotensin -like protein here.

The nucleus contains preopticus addition to afferents of the subfornical Organum also information on baroreceptors of the vascular walls of the large veins (venae cavae ) and from the right atrium of the heart. After clearing this information thirst and water search behavior is triggered. Water absorption by the missing volume is replenished, the blood pressure rises and the angiotensin II in the blood decreases. Angiotensin II has a very short half-life.