Organum subfornicale

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The organum subfornicale or subfornical organ lies on the roof of the III. Ventricle below the fornix (Latin for "vault"). It is one of the circumventricular organs with fenestrated ependyma and special ependymal cells, the tanycytes . At this point the blood-brain barrier is broken.

function

The organum subfornicale is involved in the control of the salt and water balance of the body. It is the central organ for controlling the feeling of thirst. Stimulation of the excitatory (excitatory) nerve cells of the organ leads to an immediate feeling of thirst. Stimulation of the inhibitory nerve cells of the organ leads to the immediate discontinuation of drinking.

The neurons are particularly sensitive to the hormone angiotensin II , which is produced from the zymogen angiotensinogen ( renin-angiotensin system ) when the blood pressure is too low by proteolysis by renin and conversion by the angiotensin converting enzyme (ACE ). This activation of angiotensin II takes place when the blood pressure is too low. In response to the angiotensin II stimulus, the subfornical organ sends signals via efferents to the preoptic nucleus of the hypothalamus . An angiotensin-like protein acts as a transmitter here.

In addition to the afferents of the organum subfornicale, the nucleus preopticus also receives those with information about baroreceptors in the vessel walls of the great veins ( venae cavae ) and the right atrium of the heart . After calculating this information, thirst and water-seeking behavior is triggered. The missing volume is replenished by the absorption of water, the blood pressure rises and the angiotensin II concentration in the blood decreases. Angiotensin II has a very short half-life.

literature

  • Eric R. Kandel et al .: Principles of Neural Science . McGraw-Hill Medical, 4 edition (January 5, 2000), ISBN 0-0713-9011-1

Individual evidence

  1. ↑ Brain circuit did Regulates thirst Identified. Howard Hughes Medical Institute, January 26, 2015, accessed January 28, 2015 .
  2. ↑ Yuki Oka, Mingyu Ye, Charles S. Zuker: Thirst driving and Suppressing signal encoded by distinct neural populations in the brain. In: Nature. 2015, doi : 10.1038 / nature14108 .