614
Chapter 17
SECTION B SUMMARY
Anatomy
I. The male gonads, the testes, produce sperm in the seminiferous
tubules and secrete testosterone from the Leydig cells.
Spermatogenesis
I. The meiotic divisions of spermatogenesis result in sperm
containing 23 chromosomes, compared to the original 46 of
the spermatogonia.
II. The developing germ cells are intimately associated with the
Sertoli cells, which perform many functions, as summarized in
Table 17–2.
Transport of Sperm
I. From the seminiferous tubules, the sperm pass into the
epididymis, where they are concentrated and become mature.
II. The epididymis and vas deferens store the sperm, and the
seminal vesicles and prostate secrete most of the semen.
III. Erection of the penis occurs because of vascular engorgement
accomplished by relaxation of the small arteries and passive
occlusion of the veins.
IV. Ejaculation includes emission—emptying of semen into the
urethra—followed by expulsion of the semen from the urethra.
Hormonal Control of Male Reproductive Functions
I. Pulses of hypothalamic GnRH stimulate the anterior pituitary to
secrete FSH and LH, which then act on the testes: FSH on the
Sertoli cells to stimulate spermatogenesis and inhibin secretion,
and LH on the Leydig cells to stimulate testosterone secretion.
II. Testosterone, acting locally on the Sertoli cells, is essential for
maintaining spermatogenesis.
III. Testosterone exerts a negative feedback inhibition on both the
hypothalamus and the anterior pituitary to reduce mainly LH
secretion. Inhibin exerts a negative feedback inhibition on FSH
secretion.
IV. Testosterone maintains the accessory reproductive organs and
male secondary sex characteristics and stimulates the growth
of muscle and bone. In many of its target cells, it must fi rst
undergo transformation to dihydrotestosterone or to estrogen.
Puberty
I. A change in brain function at the onset of puberty results in
increases in the hypothalamic-anterior pituitary-gonadal axis
(because of increases in GnRH).
II. The fi rst signs of puberty are the appearance of pubic and
axillary hair.
Andropause
I. The andropause is a decrease in testosterone with aging (but
usually not a complete cessation of androgen production).
Additional Clinical Examples
I. Male hypogonadism is a decrease in testicular function.
Klinefelter’s syndrome (usually XXY genotype) is a common
cause of male hypogonadism.
II. Prolactin-secreting pituitary tumors lead to
hyperprolactinemia. This causes a decrease in LH and FSH,
which results in hypogonadism.
SECTION B KEY TERMS
acrosome
608
androgen-binding protein
(ABP)
608
bulbourethral gland
606
ejaculation
610
ejaculatory duct
605
emission
610
epididymis
605
erection
610
5
α
-reductase
612
gestation
605
Leydig cell
605
libido
612
nitric oxide
610
orgasm
610
primary spermatocyte
606
prostate gland
605
puberty
612
rete testis
605
scrotum
605
secondary spermatocyte
606
semen
606
seminal vesicle
605
seminiferous tubule
605
Sertoli cell
608
Sertoli cell barrier
608
spermatic cord
605
spermatid
606
spermatogenesis
605
spermatogonium
606
vas deferens
605
SECTION B CLINICAL TERMS
andropause (male
climacteric)
613
castration
612
erectile dysfunction
610
gynecomastia
613
hyperprolactinemia
613
hypogonadism
612
Klinefelter’s syndrome
613
male pattern baldness
612
phosphodiesterase type 5
inhibitor
610
premature ejaculation
610
prostate cancer
612
vasectomy
609
SECTION B REVIEW QUESTIONS
1. Describe the sequence of events leading from spermatogonia to
sperm.
2. List the functions of the Sertoli cells.
3. Describe the path sperm take from the seminiferous tubules to
the urethra.
4. Describe the roles of the prostate gland, seminal vesicles, and
bulbourethral glands in the formation of semen.
5. Describe the neural control of erection and ejaculation.
6. Diagram the hormonal chain controlling the testes. Contrast
the effects of FSH and LH.
7. What are the feedback controls from the testes to the
hypothalamus and pituitary?
8. Defi ne puberty in the male. When does it usually occur?
9. List the effects of androgens on accessory reproductive organs,
secondary sex characteristics, growth, protein metabolism, and
behavior.
10. Describe the conversion of testosterone to DHT and estrogen.
11. How does hyperprolactinemia cause hypogonadism?
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