19.1 Introduction (p. 520)
A. Male and female reproductive systems are a series of glands and tubes that produce and nurture sex cells, and transport them to the site of fertilization.
19.2 Organs of the Male Reproductive System (p. 520; Fig. 19.1; Table 19.1) A. The male sex organs are designed to transport sperm to eggs. B. Primary sex organs (gonads) produce sperm and hormones; accessory sex organs have a supportive function. C. Testes (p. 520)
1. The testes are ovoid structures suspended by a spermatic cord in the scrotum.
2. Structure of the Testes (p. 520; Fig. 19.2)
a. Each of the testes is made up of 250 lobules separated by connective tissue; each lobule holds one to four highly coiled seminiferous tubules.
b. Seminiferous tubules are lined with stratified epithelium that gives rise to sperm cells.
c. Interstitial cells lie between the seminiferous tubules and produce the male hormones.
d. Channels leading from the seminiferous tubules carry sperm to the epididymis and vas deferens.
3. Formation of Sperm Cells (p. 521; Fig. 19.3)
a. A sperm cell has a head containing the haploid nucleus, a midpiece containing mitochondria, and a tail that is a flagellum.
b. At the tip of the head is the acrosome, a bag of digestive enzymes that helps to erode tissues surrounding the female egg cell.
4. Spermatogenesis (p. 522; Figs. 19.4-19.5)
a. In the male embryo, the spermatogenic cells are undifferentiated and are called spermatogonia; each contains 46 chromosomes.
b. During spermatogenesis, spermatogonia to enlarge and become primary spermatocytes.
c. Primary spermatocytes undergo division by meiosis and form haploid secondary spermatocytes with 23 chromosomes.
d. Secondary spermatocytes divide again to form spermatids, each of which matures into a sperm cell.
D. Male Internal Accessory Organs (p. 522)
1. The accessory organs of the male reproductive tract include the epididymides, vasa deferentia, ejaculatory ducts, urethra, seminal vesicles, prostate gland, and bulbourethral glands.
2. Epididymus (p. 522)
a. Each epididymus is a tightly coiled tube lying adjacent to the testis and leading from the testis to the vas deferens.
b. It is the site of sperm maturation. 3. Vas Deferens (p. 522) a. The vas deferens is a muscular tube 45 centimeters in length leading from the epididymus up into the body cavity to the ejaculatory duct, where it unites and empties its contents into the urethra. 4. Seminal Vesicle (p. 522) a. The seminal vesicle is a saclike structure attached to the vas deferens near the base of the urinary bladder. b. During emission, seminal vesicles secrete an alkaline fluid containing fructose to nourish sperm and prostaglandins to cause muscular contractions in the female tract to help propel sperm to the egg cell. 5. Prostate Gland (p. 524) a. The prostate gland in a chestnut-shaped structure surrounding the urethra at the base of the urinary bladder. b. The prostate gland secretes a thin, milky alkaline fluid that both enhances the mobility of sperm cells and neutralizes the acidity of the by-products produced during spermatogenesis and the acidity of the female reproductive tract. 6. Bulbourethral Glands (p. 524) a. The bulbourethral glands are small structures located inferior to the prostate that secrete mucus to lubricate the tip of the penis during sexual arousal. 7. Semen (p. 524) a. Semen is a combination of sperm cells (120 million per milliliter) and the secretions of the seminal vesicles, prostate gland, and bulbourethral glands.
c. Sperm cells cannot fertilize an egg until they undergo capacitation within the female reproductive tract. E. Male External Reproductive Organs (p. 525) 1. The male external reproductive structures are the scrotum, which houses the testes, and the penis. 2. Scrotum (p. 525) a. The scrotum is a pouch of skin and subcutaneous tissue that houses the testes suspended from…