857
CHAPTER TWENTY-TWO
Reproductive System
TABLE
22.2
|
Functions of the Female
Reproductive Organs
Organ
Function
Ovary
Produces oocytes and female sex hormones
Uterine tube
Conveys secondary oocyte toward uterus; site of
fertilization; conveys developing embryo to uterus
Uterus
Protects and sustains embryo during pregnancy
Vagina
Conveys uterine secretions to outside of body; receives
erect penis during sexual intercourse; provides open
channel for oF
spring during birth process
Labia majora
Enclose and protect other external reproductive organs
Labia minora
±orm margins of vestibule; protect openings of vagina
and urethra
Clitoris
Produces feelings of pleasure during sexual stimulation
due to abundant sensory nerve endings in glans
Vestibule
Space between labia minora that contains vaginal and
urethral openings
Vestibular
glands
Secrete ²
uid that moistens and lubricates the vestibule
structures; stimulate the endometrium to thicken; and are
also responsible for the development and maintenance of
female
secondary sex characteristics.
These are listed in
f gure 22.32
and include the following:
1. Development of the breasts and the ductile system of
the mammary glands in the breasts.
2. Increased deposition of adipose tissue in the
subcutaneous layer generally and in the breasts, thighs,
and buttocks particularly.
3. Increased vascularization of the skin.
The ovaries are also the primary source of progesterone
in a nonpregnant female. This hormone promotes changes in
the uterus during the female reproductive cycle, affects the
mammary glands, and helps regulate secretion of gonadotro-
pins from the anterior pituitary gland.
Certain other changes in females at puberty are related to
androgen
(male sex hormone) concentrations. For example,
increased growth of hair in the pubic and axillary regions is
due to androgen secreted by the adrenal cortices. Conversely,
development of the female skeletal configuration, which
includes narrow shoulders and broad hips, is a response to a
low concentration of androgen.
±emale athletes who train for endurance events, such as a marathon,
typically maintain about 6% body fat. Male endurance athletes usu-
ally have about 4% body fat. This diF
erence of 50% in proportion of
body fat re²
ects the actions of sex hormones in males and females.
Testosterone promotes deposition of protein throughout the body
and especially in skeletal muscles, whereas estrogens deposit adi-
pose tissue in the breasts, thighs, buttocks, and the subcutaneous
layer of the skin.
PRACTICE
47
What stimulates sexual maturation in a female?
48
Name the major female sex hormones.
49
What is the function of estrogens?
50
What is the function of androgen in a female?
Female Reproductive Cycle
The female reproductive cycle is characterized by regular,
recurring changes in the endometrium, which culminate
in menstrual bleeding (menses). Such cycles usually begin
near the thirteenth year of life and continue into middle
age, then cease.
A female’s first reproductive cycle, called
menarche
(me
˘-nar
ke), occurs after the ovaries and other organs of the
female reproductive control system mature and begin respond-
ing to certain hormones. Then, the hypothalamic secretion of
GnRH stimulates the anterior pituitary gland to release thresh-
old levels of FSH and LH. As its name implies, FSH stimulates
maturation of an ovarian follicle. The granulosa cells of the
22.5
HORMONAL CONTROL OF
FEMALE REPRODUCTIVE
FUNCTIONS
The
hypothalamus,
the
anterior pituitary gland,
and the
ova-
ries
secrete hormones that control development and mainte-
nance of female secondary sex characteristics, maturation of
female sex cells, and changes during the monthly reproduc-
tive cycle.
Female Sex Hormones
A female body is reproductively immature until about ten
years of age. Then, the hypothalamus begins to secrete
increasing amounts of GnRH, which, in turn, stimulate the
anterior pituitary gland to release the gonadotropins FSH and
LH. These hormones play primary roles in controlling female
sex cell maturation and in producing female sex hormones.
Several tissues, including the ovaries, the adrenal corti-
ces, and the placenta (during pregnancy), secrete female sex
hormones. These hormones include the group of
estrogens
(es
tro-jenz) and
progesterone
(pro-jes
te-ro
¯n).
Estradiol
is the most abundant of the estrogens, which also include
estrone
and
estriol.
The primary source of estrogens in a nonpregnant female
is the ovaries, although some estrogens are also synthesized
in adipose tissue from adrenal androgens. At puberty, under
the influence of the anterior pituitary gland, the ovaries
secrete increasing amounts of estrogens. Estrogens stimu-
late enlargement of accessory organs, including the vagina,
uterus, uterine tubes, and ovaries, as well as the external
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