845
CHAPTER TWENTY-TWO
Reproductive System
Hypothalamic and Pituitary Hormones
Prior to ten years of age, the male body is reproductively
immature. It is childlike, and the spermatogenic cells of the
testes are undifferentiated. Then a series of changes leads to
development of a reproductively functional adult. The hypo-
thalamus controls many of these changes.
Recall from chapter 13 (p. 497) that the hypothalamus
secretes gonadotropin-releasing hormone (GnRH), which
enters the blood vessels leading to the anterior pituitary
gland. In response, the anterior pituitary gland secretes the
gonadotropins
(go-nad
o-tro
¯p
inz) called
luteinizing hor-
mone
(LH) and
follicle-stimulating hormone
(FSH). LH, which
in males has been referred to as interstitial cell-stimulating
hormone (ICSH), promotes development of the interstitial
cells of the testes, and they, in turn, secrete male sex hor-
mones. FSH stimulates the sustentacular cells of the semi-
niferous tubules to proliferate, grow, mature, and respond
to the effects of the male sex hormone testosterone. Then, in
the presence of FSH and testosterone, these cells stimulate
the spermatogenic cells to undergo spermatogenesis, giving
rise to sperm cells
(f g. 22.18)
. The sustentacular cells also
secrete a hormone called
inhibin,
which inhibits the anterior
pituitary gland by negative feedback and thus prevents over-
secretion of FSH.
Male Sex Hormones
Male sex hormones are termed
androgens
(an
dro-jenz). The
interstitial cells of the testes produce most of them, but small
spaces partially contract again, and the veins of the penis
carry the excess blood out of these spaces. The penis gradu-
ally returns to its fl
accid state, and usually another erection
and ejaculation cannot be triggered for a period of ten to
thirty minutes or longer.
Table 22.1
summarizes the func-
tions of the male reproductive organs.
Spontaneous emission and ejaculation commonly occur in ado-
lescent males during sleep and thus are called
nocturnal emissions.
Changes in hormonal concentrations that accompany adolescent
development and sexual maturation cause these emissions.
PRACTICE
23
What controls blood f
ow into penile erectile tissues?
24
Distinguish among orgasm, emission, and ejaculation.
25
Review the events associated with emission and ejaculation.
22.3
HORMONAL CONTROL
OF MALE REPRODUCTIVE
FUNCTIONS
Hormones secreted by the
hypothalamus,
the
anterior pitu-
itary gland,
and the testes control male reproductive func-
tions. These hormones initiate and maintain sperm cell
production and oversee the development and maintenance
of male sex characteristics.
Ejaculation—semen
is forcefully
expelled from urethra
Culmination of intense
sexual stimulation
Rhythmic
contractions
in erectile
columns of
penis
Peristaltic
contractions
in testicular ducts,
epididymides,
ductus deferentia,
and ejaculatory
ducts
Rhythmic
contractions
in bulbourethral
glands, prostate
gland, and
seminal vesicles
Emission—semen moves into urethra
Sympathetic impulses contract smooth muscle
FIGURE 22.17
Mechanism oF emission and ejaculation in the male.
TABLE
22.1
|
Functions of the Male
Reproductive Organs
Organ
Function
Testis
SeminiFerous tubules
Produce sperm cells
Interstitial cells
Produce and secrete male sex hormones
Epididymis
Promotes sperm cell maturation; stores sperm
cells; conveys sperm cells to ductus deFerens
Ductus deFerens
Conveys sperm cells to ejaculatory duct
Seminal vesicle
Secretes an alkaline f
uid containing nutrients
and prostaglandins that helps neutralize the
acidic components oF semen
Prostate gland
Secretes an alkaline f
uid that helps neutralize
the acidic components oF semen and enhances
sperm cell motility
Bulbourethral gland
Secretes f
uid that lubricates end oF the penis
Scrotum
Encloses, protects, and regulates temperature
oF testes
Penis
Conveys urine and semen to outside oF
body; inserted into the vagina during sexual
intercourse; the glans penis is richly supplied
with sensory nerve endings associated with
Feelings oF pleasure during sexual stimulation
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