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The Hypothalamic-Pituitary-Gonadal Axis

     In all the mammals, the testicles have a double functional purpose: exocrine organs which produce gametes and contribute to the perpetuation of the specie, and endocrine organs that synthesize and release steroid hormones in the mammal’s organism. These two functions of the testicles are anatomically divided: Leyding cells necessary in the androgens secretion, and seminiferous tubules, which contain the spermatozoid-producing cells. The anterior pituitary gland (adenohypophysis) governs both Leyding cells and the seminiferous tubules. Two of the gonadotropins secreted by the hypophysis act as testicular-function modulators: LH, (Luteinizing Hormone) primary involved in the hypophysis- Leyding cells-axis and FSH (Follicle Stimulating Hormone) responsible with enacting seminiferous epithelial Sertoli cells.

The Function and Structure of the Leyding Cells

     The axis formed by the hypophysis and Leyding cells is composed of the GnRH (Gonadotropine Releasing Hormone), LH, testosterone, blood and blood proteins which help establish chemical reactions and carry those substances to the tissues.

     Leyding cells are situated inside the interstitial tissue which interlinks the seminiferous tubules, proximally to the sanguine capillaries.

     In a normal human fetus the testicles start to differentiate in the 6th week of pregnancy, along with spermatogenetic coordinates, and contain an elevated number of Sertoli cells. Leyding cells precursors emerge in the 8th week of pregnancy and they became fully differentiate in the 10th week of gestation.

     Testosterone is produced in human fetus’s testicles during the 6th -7th week of pregnancy and it can be found in its blood, tissue and in the amniotic liquid, gradually increasing up to a maximum level in the 15th – 18th week. Along with the increased testosterone level, the number of Leyding is also elevated and in the 14th -15th occupies more than 50% of the testicular volume. After this burst of activity Leyding cells development stagnates. Posterior to the 16th week the testosterone level decreases. At birth the Leyding cells number is reduced by 60% and each cell had lost half of its volume. These changes are accompanied of the reduction of the hCG (Human chorionic gonadotropin). Testosterone has a rebound after 2 months of the new-born male coordinated with a second wave of Leyding cells differentiation. Their number increases and then, degenerates and in the first year of life there are only few Leyding cells left in the body. The last stage of Leyding cells development is puberty, when the undifferentiated tissues from the testicles change their structure and function due to LH’s influences. During puberty and adolescence Leyding cells increase their number and reach a pinnacle of 5x 100.0000.000 cells/testicle at the age of 20, after this age the number gradually decreases until the age of 60 years.

     The main response of the Leyding cells to LH consists in the production and secretion of testosterone. LH and hCG are critical for Leyding cells regulation and proliferation.

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