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Chapter 17
from a complex interplay between the sex steroids and brain
neurotransmitters.
Androgens in Women
Androgens are present in the blood of women as a result
of production by the adrenal glands and ovaries. These
androgens play several important roles in the female, includ-
ing stimulation of the growth of pubic hair, axillary hair,
and, possibly, skeletal muscle, and maintenance of sex drive.
Excess androgens may cause
virilism
:
the female fat dis-
tribution disappears, a beard appears along with the male
body hair distribution, the voice lowers in pitch, the skeletal
muscle mass enlarges, the clitoris enlarges, and the breasts
diminish in size.
Puberty
Puberty in females is a process similar to that in males (described
earlier in this chapter). It usually starts earlier in girls (10 to 12
years old) than in boys. In the female, GnRH, the pituitary
gonadotropins, and estrogen are all secreted at very low levels
during childhood. For this reason, there is no follicle matura-
tion beyond the early antral stage, and menstrual cycles do not
occur. The female accessory sex organs remain small and non-
functional, and there are minimal secondary sex characteristics.
The onset of puberty is caused, in large part, by an alteration
in brain function that increases the secretion of GnRH. This
hypophysiotropic hormone in turn stimulates the secretion of
pituitary gonadotropins, which stimulate follicle development
and estrogen secretion. Estrogen, in addition to its critical role
Table 17–8
Some Effects of Female Sex Steroids
Estrogen
1. Stimulates growth of ovary and follicles (local effects)
2. Stimulates growth of smooth muscle and proliferation of epithelial linings of reproductive tract. In addition:
a. Fallopian tubes: Increases contractions and ciliary activity.
b.
Uterus: Increases myometrial contractions and responsiveness to oxytocin. Stimulates secretion of abundant, watery cervical
mucus. Prepares endometrium for progesterone’s actions by inducing progesterone receptors.
c. Vagina: Increases layering of epithelial cells.
3. Stimulates external genitalia growth, particularly during puberty
4. Stimulates breast growth, particularly ducts and fat deposition during puberty
5. Stimulates female body confi guration development during puberty: narrow shoulders, broad hips, female fat distribution (deposition
on hips and breasts)
6. Stimulates fl uid secretion from lipid (sebum)-producing skin glands (sebaceous glands). (This “anti-acne” effect opposes the acne-
producing effects of androgen.)
7. Stimulates bone growth and ultimate cessation of bone growth (closure of epiphyseal plates); protects against osteoporosis; does not
have an anabolic effect on skeletal muscle
8. Vascular effects (defi ciency produces “hot fl ashes”)
9. Has feedback effects on hypothalamus and anterior pituitary (see Table 17–4)
10. Stimulates prolactin secretion but inhibits prolactin’s milk-inducing action on the breasts
11. Protects against atherosclerosis by effects on plasma cholesterol (Chapter 16), blood vessels, and blood clotting (Chapter 12)
Progesterone
1. Converts the estrogen-primed endometrium to an actively secreting tissue suitable for implantation of an embryo
2. Induces thick, sticky cervical mucus
3. Decreases contractions of fallopian tubes and myometrium
4. Decreases proliferation of vaginal epithelial cells
5. Stimulates breast growth, particularly glandular tissue
6. Inhibits milk-inducing effects of prolactin
7. Has feedback effects on hypothalamus and anterior pituitary (see Table 17–4)
8. Increases body temperature
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