>>Dr. Ketchum: This video will discuss the
hormonal regulation of male reproduction. Let’s start with what you are already familiar
with—that is the hypothalamus and the synthesis and secretion of gonadotropin-releasing hormone,
GnRH. Once secreted, gonadotropin-releasing hormone will bind to receptors on the anterior
pituitary, causing the endocrine cells to synthesize and secrete both FSH and LH. FSH
stands for follicle stimulating hormone, and LH, remember, is luteinizing hormone. LH,
as we discussed in previous videos, will stimulate the Leydig cells of the testes to synthesize
and secrete testosterone. Testosterone will then enter the plasma and cause target cell
responses. Let’s review those responses. Testosterone will target skeletal muscle,
causing protein synthesis. Testosterone will target the brain to increase sex drive. It
will also target the Sertoli cells to stimulate spermatogenesis. Testosterone will promote
the development of secondary sex characteristics and the maintenance of those characteristics.
Here are a couple of other responses that we have not yet talked about. Testosterone
will stimulate growth hormone (GH) secretion, which will stimulate bone growth during adolescence.
And finally, testosterone will stimulate the Wolffian ducts to promote development of male
reproductive structures during embryonic life. Now let’s turn our attention to FSH. Like
LH, FSH will bind to receptors on the Sertoli cells to stimulate spermatogenesis, as well
as the synthesis and secretion of a protein hormone called inhibin. Since we are talking
about inhibin, this is a good time to talk about how to shut down the system. You are
already familiar with negative feedback using testosterone. Remember, testosterone will
bind to receptors on the hypothalamus and the anterior pituitary. This will shut off
the synthesis and secretion of gonadotropin-releasing hormone and luteinizing hormone. Inhibin will
bind to the anterior pituitary and shut off the synthesis and secretion of FSH. To sum
it all up, negative feedback shuts off the synthesis and secretion of gonadotropin-releasing
hormone, luteinizing hormone, and follicle stimulating hormone, which will all lead to
the decrease in the synthesis and secretion of testosterone.

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