The male gonads are the testes. They serve two important functions - they act as both a reproductive gland as well as an endocrine gland. In this lecture, we shall focus on its endocrine ability. The testes produce a group of hormones called androgens, which simply means male sex hormones. Inside the testes is a structure called the seminiferous tubules, which consists of two important cells - the Leydig cells (also called interstitial cells) and Sertoli cells. Both of these cells are crucial in sperm production. The luteinizing hormone (LH) released by the anterior pituitary gland stimulates the Leydig cells to release an androgen called testosterone. Testosterone is a steroid hormone and it (a) initiates the production of sperm cells (b) gives us secondary sex characteristics such as pubic hair and a larger larynx (deeper voice) (c) initiates the process of puberty, which involves an increase in both muscle mass and bone mass (d) helps prevent osteoporosis (e) closes the epiphyseal plate in our long bones, which ends the elongation of long bones. Increasing levels of testosterone in our blood will create a negative feedback loop that will ultimately inhibit the release of the gonadotropin-releasing hormone of the hypothalamus as well as the follicle stimulating hormone and luteinizing hormone of the anterior pituitary gland. In this way, our body can control the level of testosterone found in our blood. The Sertoli cells, which are stimulated by the follicle-stimulating hormone to provide nutrition to developing sperm cells, can release a hormone called inhibin which goes on to the anterior pituitary gland and blocks the release the follicle-stimulating hormone.
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