Chapter 27 : The male reproductive system

Male Reproductive System

• The functions of the male reproductive system are to produce sperm, introduce sperm into the female body, and produce steroid hormones.

• Consists of primary sex organs (the gonads = the testes) and secondary sex organs (the penis, scrotum, vas deferens, prostate gland, bulbourethral glands, and seminal vesicles).

The Testes

• Sperm are produced inside coiled tubules called the seminiferous tubules.

• The tubules are lined with several layers of germ cells that are in the process of becoming sperm as well as some nurse cells, which support the germ cells and produce androgen-binding protein and inhibin.

• Testosterone is produced by the interstitial cells, also known as Leydig cells, that are found in between the tubules.

Spermatogenesis

• Spermatogenesis is the process of sperm formation. It is achieved through meiosis, in which a single diploid cell gives rise to four haploid cells.

• The diploid cells in this case are called spermatogonia. Under the direction of testosterone, they will undergo meiosis to become spermatids.

• As the cells go through the stages of meiosis, they migrate from the edge of the seminiferous tubules to the core.

• Spermatids must transform into sperm. They grow a flagellum and get rid of most of their cytoplasm, except for mitochondria in the midpiece that power the flagellum and a sac in the head called the acrosome, which contains enzymes to penetrate the egg if contact is made.

• The head also contains the genetic material.

• At this stage the sperm are not fully mature. They cannot yet move on their own.

Male Reproductive Tract

• After being formed in the seminiferous tubules, the immature sperm move to the epididymis.

• The sperm are moved along by fluid from the nurse cells and by the actions of cilia on the cells of the ducts.

• The epididymis, located on the posterior side of the testis, is the site of sperm maturation and storage. It consists of a series of tubules.

• The epididymis leads into the vas deferens. The vas deferens continues until it merges with the urethra.

Accessory Glands

• The seminal vesicles, prostate gland, and bulbourethral glands all secrete materials that comprise the semen.

• Semen has two main functions:
  – It provides nutrients for the sperm in the form of sugars (fructose) and ions (calcium, phosphate, citrate).
  – It helps to buffer the acidic pH of the female reproductive tract.

Hormonal Control of Function

• During the first trimester, the testes in the fetus secrete large amounts of testosterone. Even during the first few months after birth, testosterone levels are as high as they are during puberty. The purpose of elevated testosterone at that time is to direct the development of the internal and external reproductive structures (the secondary sex organs). After that, the testes become dormant until puberty.

• As puberty begins, the hypothalamus produces more GnRH gonadrotropin-releasing hormone), which causes the release of LH (luteinizing hormone) and FSH (follicle-stimulating hormone) from the anterior pituitary.

• LH causes the interstitial cells to produce testosterone. Testosterone promotes sperm production. It also causes the development of secondary sex characteristics, enhances libido and promotes territorial and aggressive behaviors.

• FSH stimulates the nurse cells to secrete androgen-binding protein, which holds testosterone in the seminiferous tubules.

• Nurse cells also secrete inhibin, which functions in a negative feedback loop to inhibit the release of FSH from the anterior pituitary.

• Testosterone has an inhibitory effect on the release of GnRH.