Q.Describe briefly the hormonal regulation of spermatogenesis.

[!TLDR]

GnRH from the hypothalamus stimulates pituitary LH and FSH; LH drives Leydig-cell testosterone, FSH acts on Sertoli cells, and inhibin from Sertoli cells feeds back to limit further FSH.

[!ANSWER]

GnRH -> LH (-> Leydig cells -> testosterone) and FSH (-> Sertoli cells); testosterone + FSH together sustain spermatogenesis; Sertoli-cell inhibin gives negative feedback on FSH.

Spermatogenesis is regulated along the hypothalamus-pituitary-testis axis. GnRH secreted by the hypothalamus stimulates the anterior pituitary to release LH and FSH. LH acts on the Leydig cells of the testis, stimulating them to secrete testosterone, which acts both systemically and locally within the seminiferous tubule to support spermatogenesis. FSH acts directly on the Sertoli cells, stimulating them to secrete androgen-binding protein (which concentrates testosterone within the tubule) and other factors needed for spermatogenesis to proceed. Sertoli cells also secrete inhibin, which feeds back negatively on the anterior pituitary to reduce further FSH secretion once sperm output is adequate, keeping the whole axis balanced.

[!ANSWER]

GnRH -> LH (-> Leydig cells -> testosterone) and FSH (-> Sertoli cells); testosterone + FSH together sustain spermatogenesis; Sertoli-cell inhibin gives negative feedback on FSH.

Trace the axis top to bottom (hypothalamus -> pituitary -> testis) and then note the feedback loop (inhibin -> pituitary) that closes it.

Naming only testosterone and omitting FSH's independent, direct action on the Sertoli cells -- both hormones act together and neither alone is sufficient for normal spermatogenesis.