In mankind, the reproductive function is controlled by nervous and hormonal correlations, that is, by the nervous and endocrine systems, which complement each other.
The central nervous system, sensitive to external and internal (endogenous) stimuli, transmits its messages by processing neurotransmitters.
The hypothalamus belongs to the central nervous system but, from a functional point of view, its neurons are capable of receiving signals that arrive both from the upper nervous structures and from the glands of the endocrine system (pituitary and gonads for example), which are not nerve structures: it is therefore the place where the connections between the central nervous system and the endocrine (hormonal) system occur.
The hormones produced by the hypothalamus are of a protein nature (while those produced by the gonads are derivatives of cholesterol, and therefore of a lipid nature) and act on the pituitary. It is divided into two portions, an anterior, or adenohypophysis, and a posterior, or neurohypophysis.
The adenohypophysis is connected to the hypothalamus by a system of blood vessels into which the hypothalamic hormones are introduced which thus reach the hypophysis. In the same way, always through this system, the hormones produced by the hypophysis can reach the hypothalamus and influence it. the function.
Hypothalamic hormones determine, at the level of the adenohypophysis, the synthesis, the accumulation, therefore the introduction into the blood of a series of products that are called tropins as they act on other glands of the endocrine system that are dependent on the pituitary gland (ovary, testicle, thyroid, breast, adrenal cortex, function of growth etc ...).
Hypothalamic hormones are referred to as Relasing Hormones (RH), ie substances that stimulate the elimination and entry into the blood of pituitary hormones.
The RH are:
The GnRH or relasing hormone for the two pituitary gonadotropins LH and FSH, acting on the ovaries for the induction of ovulation;
A relasing hormone for pituitary thyroid stimulin or TRH acting on the thyroid gland;
A relasing hormone for pituitary growth hormone or GHRH;
A relasing hormone for tropin which stimulates the adrenal cortex or CRH, in turn causing it to produce the hormone cortisol;
Similarly, there are also hormones that inhibit the secretion of the pituitary gland if this is necessary.
Under the stimulus or inhibition of the hypothalamus, the adenohypophysis produces a series of hormones or tropins of a protein nature and other substances, such as endorphins, which are also found in the brain and have a chemical structure that resembles that of opioids. .
Pituitary hormones are represented by:
Gonadotropin FSH (follicle stimulating hormone);
Gonadotropin LH (luteinizing hormone);
ICSH (hormone stimulating the interstitial cells of the testis) in man;
Prolactin, important in the preparation of the mammary gland during pregnancy and in its function during lactation. Outside the pregnancy, non-physiological levels of prolactin can negatively influence the mechanisms of fertility, and therefore of reproduction;
The TSH (thyroid stimulating tropin);
L"ACTH (tropin stimulating the adrenal cortex);
The GH (tropin stimulating body growth);
In addition, the pituitary gland produces opioid peptides (endorphins) and factors that affect the liver and pancreas.
Gonadotropins act on the gonads (ovary and testicle). The ovary, under the stimulus of gonadotropins, secretes three hormones that derive from cholesterol: estrogens, androgens, progesterone and its derivatives.
In the pituitary there is also a posterior lobe with a nervous structure, called neurohypophysis, which they reach directly from the hypothalamus, this time not through the blood but through extensions of neurons, a series of substances produced by the neurons of the hypothalamus itself. then released into the bloodstream and have actions on the whole organism. Among them, the most important are the "ADH or antidiuretic hormone or vasopressin, responsible for sodium retention, and the"oxytocin, which stimulates the contraction of the muscles of the uterus during childbirth and of the muscle cells (myoepithelial) of the breast during breastfeeding to facilitate the release of milk.
