Section 16.1-2Section 16.1-2Hormonal Control of the Male Reproductive Hormonal Control of the Male Reproductive

SystemSystem

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.

Primary 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

Secondary Sexual Characteristics

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

Male Reproductive Hormones

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. Gonadotropin Releasing Hormone (GnRH)•produced by the hypothalamus•stimulates 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.

Negative Feedback Systems for FSH and LH

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.