Chapter 16. Section 16.1-2 Hormonal Control of the Male Reproductive System. Primary Sexual Characteristics. Primary sexual characteristics – physical characteristics of an organism that are directly involved in reproduction. Includes all the structures of the male reproductive system.
Chapter 16 Section 16.1-2 Hormonal Control of the Male Reproductive System
Primary Sexual Characteristics • Primary sexual characteristics – physical characteristics of an organism that are directly involved in reproduction. • Includes all the structures of the male reproductive system. • Examples for males: • testes • seminiferous tubules • epididymis • vas deferens • etc.
Secondary Sexual Characteristics • Secondary sexual characteristics – external features of an organism that are indicative of its gender, but are not reproductive organs themselves. • Examples for males: • chest and abdominal hair • facial hair • more hair in armpits • deeper voice
Male Reproductive Hormones • 4 male reproductive hormones: 1. Testosterone • produced by the interstitial cells • interstitial cells are found in the testes surrounding the seminiferous tubules • stimulates spermatogenesis • promotes and regulates the secondary sex characteristics • associated with sex drive levels
Site of Testosterone Production Testosterone is produced in interstitial cells that surround the seminiferous tubules.
2. Follicle Stimulating Hormone (FSH) • gonadotrophic hormone – hormone produced by the pituitary that regulates the function of the testes in males • produced by the pituitary gland • stimulates the production of sperm cells in the seminiferous tubules
3. Luteinizing Hormone (LH) • gonadotrophic hormone • produced in the pituitary gland • promotes the production of testosterone by the interstitial cells
4. GonadotropinReleasing Hormone (GnRH) • produced by the hypothalamus • stimulates FSH and LH
Negative Feedback Systems for FSH and LH • Beginning at puberty when testosterone is low, the hypothalamus secretes GnRH. • GnRH activates the pituitary gland to secrete FSH and LH. • FSH acts directly on the sperm producing cells of the seminiferous tubules – the Sertoli cells. • LH stimulates testosterone production in the interstitial cells.
Testosterone then promotes spermatogenesis. • When sperm counts are high, the Sertoli cells of the seminiferous tubules produce a hormone called inhibin. • Inhibin sends a feedback message to the pituitary to stop the production of FSH, also causes the hypothalamus to reduce the production of GnRH. • When testosterone levels are high, the pituitary stops producing LH and the hypothalamus reduces the production of GnRH.