The hypothalamus is a bunch of nervous cells of the Cerveau which controls inter alia, thanks to its direct links with the Hypophyse (the hypophyseal stem) producing of Hormone S:

This bond is carried out via neurons connected with the Système carries hypophyseal. It is about the only case where a Neurotransmetteur, in this case named Neurohormone, is poured directly in blood by a synaptic termination. The hypothalamus has two types of neuronal cores cellular:

  • parvicellulaires
  • magnocellulaires

Example of GnRH

A Neurohormone, the GnRH ( Gonadotropin releasing hormone ) is synthesized by these neurons then released in a pulsatile way in the Sang: the hypothalamus sends potentials of actions through the Neuron. Thereafter, GnRH acts on the cells of the pituitary gland. The GnRH connection with the hypophyseal cells involves the release of folliculostimulante (FSH) and hormone lutéinisante (LH), which are of glycoproteic nature. The FSH stimulates indirectly the Spermatogenèse in the Testicules. It makes the cells receptive to the stimulative effects of testosterone. The LH binds to the interstitial cells and stimulates them so that they secrete testosterone. The increase in the concentrations of Testosterone and inhibine exerts an retro-inhibition on the hypothalamus and the Hypophyse.

The hypothalamo-hypophyseal complex

The hypothalamus is connected to the pituitary gland by the pituitary stem. The junction hypothalamus/ante-pituitary gland is carried out by blood way while the post-pituitary gland is really connected to the hypothalamus by the pituitary stem, consisted the axons of the neurons hypothalamic. The FSH (Follicle Stimulating Hormone) and the LH (Luteinizing Hormone), two Hormone S hypophyseal stimulate the estrogen production of S and of Progestérone by the ovary S. One calls them the Gonadonostimuline S (or Gonadotropin). The FSH intervenes in the maturation of the follicules. An abrupt rise in the concentration of the rate of LH (peak of LH) at the follicular end of the phase starts the Ovulation and causes the transformation of the follicule broken into yellow body. Hypophyseal secretions are themselves under the control of the hypothalamus which secretes a substance Neurohormone (GnRH). The hormones ovariennes (estrogen and progesterones) exert a control in return or retro-control on the hypothalamo-hypophyseal complex: they inhibit the secretion of LH and FSH during the major part of the cycle (negative retro-control). Conversely, the estrogens stimulate the secretion of LH and FSH as soon as they cross a concentration threshold in the blood plasma (approximately 200 pg per ml of plasma), which is the case right before ovulation (positive retro-control). They are these cyclic secretions of the hormones which induce the cyclic modifications of the reproductive apparatus of the women. External stimuli coming from the environment can via the central nervous system influence the hypothalamo-hypophyseal complex and thus the sexual cycles. The hypathalamo-hypophyseal complex takes into account the variations of the hormones ovariennes and the factors of the environment. It thus carries out an integration of multiple messages nervous and hormonal in order to control the sexual cycles, which can be at the origin of a shift of the normal cycle ovarien at the woman for example (strong emotions…).

At the man, the LH acts on the cells of Leydig (interstitial cells) which will produce testosterone. The FSH acts on the cells of Sertoli, persons in charge of the good progress of the spermatogénèse. The cells of Sertoli and Leydig are located in the testicle. The testosterone thus secreted will see its rate constantly analyzed by the hypothalamo-hypophyseal complex. It will have a negative feedback on this complex, if the testosteronimy is too important, in order to lower pulsatile secretions of GnRH, FSH and LH.

Hypothalamique hormones

Dopamine, Somatolibérine, Somatostatine, TRH, GNRH

These hormones move towards the Pituitary gland thanks to the system carries Hypothalamo-Hypophyseal

ADH Ocytosine

External bonds

    Video
  • diaporamic of the hypothalamus, by Dr. Dominique Hasboun (course under video requiring the video decoder free Distens)

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