Final answer:
Spermatogenesis is initiated by the hypothalamic hormone gonadotropin-releasing hormone (GnRH), which triggers the release of FSH and LH from the pituitary gland, leading to the production of testosterone by Leydig cells and the start of spermatogenesis.
Step-by-step explanation:
Spermatogenesis is initiated by the hormone called gonadotropin-releasing hormone (GnRH), which is produced by the hypothalamus. This hormone stimulates the release of two other important hormones from the anterior pituitary gland: follicle-stimulating hormone (FSH) and luteinizing hormone (LH). FSH primarily targets Sertoli cells in the testes to promote spermatogenesis, while LH stimulates the Leydig cells to produce testosterone, essential for the maturation of sperm cells and the development of secondary sex characteristics.
The regulation of testosterone synthesis and spermatogenesis is a complex process involving a feedback loop. High levels of testosterone and inhibin, a hormone produced by the Sertoli cells, provide negative feedback to the hypothalamus and pituitary gland to regulate the production of GnRH, LH, and FSH, maintaining the balance of hormone levels.