Fundamentals of Anatomy and Physiology

The Reproductive System

The Uterus

1. The uterus is the site of menstruation, it is where the
   fertilized egg is implanted and where the fetus de-

velops, and it is where labor begins during delivery.^

2. It is shaped like an inverted pear: the dome-shaped
   portion above the uterine tubes is the fundus, the
   major tapering portion the body, and the narrow
   inferior portion the cervix. Between the body and the

cervix is a narrow region called the isthmus.^

3. The interior of the body is the uterine cavity; the

interior of the cervix is the cervical canal.^

4. The opening between the uterine cavity and the cer-
   vical canal is called the internal os, and the opening
   between the cervical canal and the vagina is the

external os.^

5. The wall of the uterus is composed of three layers: the
   innermost is the endometrium where the fertil-ized
   egg implants, the second is the myometrium of
   smooth muscle, and the outermost is the perime-trium
   or visceral peritoneum.

The Menstrual Cycle

1. The menstrual cycle, also called the menses or
   menstruation, is the cyclical shedding of the endo-

metrial lining of the uterus.^

2. The three phases are the menstrual phase, the pro-

liferative phase, and the secretory phase.^

3. During the menstrual phase, the endometrial lining of
   the uterus, tissue fluid, blood, and mucus are shed.
   Twenty to 25 primary follicles also begin their devel-
   opment and produce low levels of estrogen. The zona
   pellucida develops around each egg and about 20
   primary follicles become secondary follicles, but only

one attains maturity while the others die.^

4. During the proliferative phase, one of the second-ary
   follicles matures into a graafian follicle with a single
   mature egg. The egg ruptures from the follicle in a
   process called ovulation, and rising estrogen levels
   cause the endometrial lining of the uterus to thicken.
   After ovulation, the graafian follicle col-lapses with a
   clot inside called the corpus hemor-rhagicum, which is
   eventually absorbed. The follicle eventually changes
   character and becomes the cor-pus luteum.


5. During the secretory phase, the corpus luteum begins
   to secrete estrogen and progesterone. If fertilization
   and implantation do not occur, the cor-pus luteum
   degenerates and becomes the corpus albicans. If
   fertilization and implantation do occur,

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the corpus luteum is maintained for 4 months by

human chorionic gonadotropin produced by the

developing placenta.^

6. Once the placenta is developed, it will secrete es-
   trogen to support pregnancy and progesterone to
   support pregnancy and breast development for milk
   production in the mammary glands.

The Functions of Estrogen

1. The ovaries become active during puberty produc-ing
   ova and estrogen.^


2. Estrogen causes the development of the female
   secondary sex characteristics: the development of
   breasts; the appearance of pubic and axillary hair; fat
   deposits on the hips, breasts, and under the skin; and
   widening of the pelvic bone producing a broad hip.


3. Estrogen causes enlargement of the uterine tubes,
   uterus, vagina, and the external genitalia.

The Vagina

1. The vagina is a passageway for the menstrual flow, is a
   receptacle for the penis during sexual intercourse, and
   is the lower portion of the birth canal.^


2. A recess called the fornix surrounds the vaginal at-
   tachment to the cervix.

The External Genitalia of the Female

1. The vulva or pudendum is the collective term for
   the external genitalia of the female.^


2. The mons pubis or veneris is a mound of adipose
   tissue covered with pubic hair at puberty.^


3. Two longitudinal folds of hair-covered skin extend
   posteriorly and inferiorly from the mons pubis called
   the labia majora. They contain adipose tissue and
   sweat glands.^


4. Medial to the labia majora are two other delicate
   folds of skin called the labia minora. They do not
   have hair but have numerous sebaceous glands.^


5. The clitoris is a small mass of erectile tissue located at
   the anterior junction of the labia minora covered with
   a layer of skin called the prepuce. The exposed
   portion of the clitoris is called the glans.^


6. The opening between the two labia minora is called
   the vestibule containing a thin fold of tissue called the
   hymen, which is ruptured during the first sexual
   intercourse.