Anatomy and physiology. The male reproductive system.

The male reproductive hormonal axis Maintenance of normal reproductive function is depend­ ent on the coordinated release of hormones in the hyp o­ thalamic−pituitary−testis cascade. Gonadotropin­releasing hormone (GnRH) is released in a pulsatile pattern into the pitu­ itary portal blood system from neuroendocrine cells in the basal hypothalamus and acts to stimulate gonadotropes in the anter­ ior pituitary to synthesize and release two peptide hormones, follicle­stimulating hormone (FSH) and luteinizing hormone (LH) into the circulation. Once in the bloodstream these hor­ mones reach the testis, where LH stimulates testosterone production by the Leydig cells in the interstitium while FSH supports spermatogenesis in the seminiferous epithelium by stimulation of the Sertoli cells. A focused network of negative feedback relationships finesse testosterone secretion and sperm production. This cascade is maintained by steroid and peptide feedback within the testis as well as the hypothalamic and pitu­ itary gland (see Figure 1.1).