The Hypothalamicpituitarytesticular Axis

The hypothalamic-pituitary-testicular axis coordinates two principal functions that are essential for reproduction in males: the production of physiologic quantities of sex steroid hormones, primarily testosterone, and the generation of spermatogenic cells that become mature gametes capable of fertilizing oocytes. Gonadotropin-releasing hormone (GnRH) is the primary regulator of this system. It is released into the portal blood in discrete pulses and binds to specific receptors on gonadotropic cells, where it stimulates the synthesis and release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). LH and FSH, in turn, control development, maturation, and function of the gonad through interaction with specific membrane receptors (1). To induce and maintain quantitatively normal spermatogenesis in humans, both gonadotropins are required (2). LH binds to Leydig cells to initiate testosterone synthesis and secretion, whereas FSH binds to Sertoli cells and stimulates the production of several factors that, together with testosterone from Leydig cells, induce and maintain spermatogenesis (1).

From: Male Hypogonadism: Basic, Clinical, and Therapeutic Principles Edited by: S. J. Winters © Humana Press Inc., Totowa, NJ

Underlying Cause secondary hypo gonad is m/

hypogonadotropic hypogonadism primary hypogonadism/ hypergonadotropic hypogonadism

Klinefelter syndrome

Fig. 1. Treatment of hypogonadism according to pathogenesis.

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