Testosterone secretion, regulation

Figure 19.11 Hormones secreted by the hypothalamus, anterior pituitary, ovary and testis and feedback regulation. GnRH is gonadotrophin-releasing hormone the gonadotrophins are follicle-stimulating hormone (FSH) and luteinising hormone (LH). The effect of these hormones on activities in the ovary and testes is shown. FSH stimulates synthesis and secretion of oestradiol from follicle, and spermatogenesis in testis. LH stimulates synthesis and secretion of progesterone from corpus luteum and synthesis and secretion of testosterone by the Leydig cells.

Since FSH and LH are involved in spermatogenesis, hypothalamic control of their release by the pituitary is important for testicular function. Both FSH and LH are secreted in a pulsatile fashion from the pituitary. Inhibin produced by Sertoli cells has the most important negative feedback effect on FSH secretion, while testosterone exerts negative feedback effects on secretion of GnRH by the hypothalamus, thus regulating secretion of LH and, to a lesser extent, FSH. 

The adrenocorticotrophic hormone ACTH (corticotropin) stimulates the adrenal cortex to secrete the glucocorticoids hydrocortisone (cortisol) and corticosterone, the mineralocorticoid aldosterone, and a number of weakly androgenic substances, as well as a small amount of testosterone. Aldosterone synthesis is also regulated by renin and angiotensin. 

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