M

external ive Organ:

Daughters of women who took the drug DES (diethyl-stilbestrol) while pregnant with them may develop a benign condition called adenosis. It arises when secretory columnar epithelium, resembling normal cells of the uterine lining, grow in the wrong place — in the vagina, up near the cervix. It is a little as if the lining of the mouth were to grow onto the face.

Adenosis may produce a slight vaginal discharge. It is detected with a procedure called the Pap (Papanicolaou) smear test. A doctor or nurse scrapes off a tiny sample of cervical tissue, smears the sample on a glass slide, and sends it to a laboratory, where cytotechnolo-gists stain and examine it for the presence of abnormal cells, or a computer with image-analysis software scans it.

If the Pap smear is abnormal, the doctor follows up with a direct observation with a special type of microscope called a colposcope. The physician paints the patient's cervix with acetic acid (vinegar), which stains a purplish blue in the presence of carbohydrate in the discharge. A laser can be used to painlessly remove the abnormally placed tissue.

The middle muscular layer of the vagina mainly consists of smooth muscle fibers in longitudinal and circular patterns. At the lower end of the vagina is a thin band of striated muscle. This band helps close the vaginal opening; however, a voluntary muscle (bulbospon-giosus) is primarily responsible for closing this orifice.

The outer fibrous layer consists of dense connective tissue interlaced with elastic fibers. It attaches the vagina to surrounding organs.

99 How does an egg cell move into the infundibulum following ovulation?

^9 How is an egg cell moved along a uterine tube?

^9 Describe the structure of the uterus.

□ What is the function of the uterus?

Q Describe the structure of the vagina.

The external accessory organs of the female reproductive system include the labia majora, the labia minora, the clitoris, and the vestibular glands. These structures that surround the openings of the urethra and vagina compose the vulva (fig. 22.30).

Labia Majora

The labia majora (sing., labium majus) enclose and protect the other external reproductive organs. They correspond to the scrotum of the male and are composed of rounded folds of adipose tissue and a thin layer of smooth muscle, covered by skin. On the outside, this skin includes hairs, sweat glands, and sebaceous glands, whereas on the inside, it is thinner and hairless.

The labia majora lie closely together and are separated longitudinally by a cleft (pudendal cleft), which includes the urethral and vaginal openings. At their anterior ends, the labia merge to form a medial, rounded elevation of adipose tissue called the mons pubis, which overlies the symphysis pubis. At their posterior ends, the labia taper and merge into the perineum near the anus.

Labia Minora

The labia minora (sing., labium minus) are flattened longitudinal folds between the labia majora, and they extend along either side of a space called the vestibule. They are composed of connective tissue richly supplied with blood vessels, causing a pinkish appearance. Stratified

Clitoris

Urethral orifice

Vaginal orifice

Urethral orifice

Vaginal orifice

Mons pubis

Labium majus

-Vestibule

-Labium minus

Mons pubis

Labium majus

-Vestibule

-Labium minus

Perineum Anus

Figure 22.30

Female external reproductive organs.

squamous epithelium covers this tissue. Posteriorly, the labia minora merge with the labia majora, whereas anteriorly, they converge to form a hoodlike covering around the clitoris.

Clitoris

The clitoris (klit'o-ris) is a small projection at the anterior end of the vulva between the labia minora. It is usually about 2 centimeters long and 0.5 centimeters in diameter, including a portion embedded in surrounding tissues. The clitoris corresponds to the penis and has a similar structure. It is composed of two columns of erectile tissue called corpora cavernosa. A septum separates these columns, which are covered with dense connective tissue.

At the root of the clitoris, the corpora cavernosa diverge to form crura, which, in turn, attach to the sides of the pubic arch. At its anterior end, a small mass of erectile tissue forms a glans, which is richly supplied with sensory nerve fibers.

Vestibule

The labia minora enclose the vestibule. The vagina opens into the posterior portion of the vestibule, and the urethra opens in the midline, just anterior to the vagina and about 2.5 centimeters posterior to the glans of the clitoris.

A pair of vestibular glands (Bartholin's glands), corresponding to the bulbourethral glands in the male, lie on either side of the vaginal opening. Their ducts open into the vestibule near the lateral margins of the vaginal orifice.

Beneath the mucosa of the vestibule on either side is a mass of vascular erectile tissue. These structures are called the vestibular bulbs. They are separated from each other by the vagina and the urethra, and they extend forward from the level of the vaginal opening to the clitoris.

O What is the male counterpart of the labia majora? Of the clitoris?

^9 What structures are within the vestibule?

Erection, Lubrication, and Orgasm

Erectile tissues located in the clitoris and around the vaginal entrance respond to sexual stimulation. Following such stimulation, parasympathetic nerve impulses from the sacral portion of the spinal cord inhibit sympathetic control of the arteries associated with the erectile tissues, causing them to dilate. As a result, inflow of blood increases, tissues swell, and the vagina begins to expand and elongate.

If sexual stimulation is sufficiently intense, parasympathetic impulses stimulate the vestibular glands to secrete mucus into the vestibule. This secretion moistens and lubricates the tissues surrounding the vestibule and the lower end of the vagina, facilitating insertion of the penis into the vagina. Mucus secretion continuing during sexual intercourse helps prevent irritation of tissues that might occur if the vagina remained dry.

The clitoris is abundantly supplied with sensory nerve fibers, which are especially sensitive to local stimulation. The culmination of such stimulation is orgasm, the pleasurable sensation of physiological and psychological release.

Just prior to orgasm, the tissues of the outer third of the vagina engorge with blood and swell. This action increases the friction on the penis during intercourse. Orgasm initiates a series of reflexes involving the sacral and lumbar portions of the spinal cord. In response to these reflexes, the muscles of the perineum and the walls of the uterus and uterine tubes contract rhythmically. These contractions help transport sperm cells through the female reproductive tract toward the upper ends of the uterine tubes (fig. 22.31).

Following orgasm, the flow of blood into the erectile tissues slackens, and the muscles of the perineum and reproductive tract relax. Consequently, the organs return to a state similar to that prior to sexual stimulation. Table 22.2 summarizes the functions of the female reproductive organs.

O What events result from parasympathetic stimulation of the female reproductive organs?

^9 How does the vagina change just prior to and during female orgasm?

B How do the uterus and the uterine tubes respond to orgasm?

Sexual stimulation

Parasympathetic nerve impulses from the sacral portion of the spinal cord

Sexual stimulation intensifies

Vestibular glands secrete mucus to lubricate

Orgasm—rhythmic contraction of muscles of the perineum; muscular walls of uterus and uterine tubes contract

Figure

Mechanism of erection, lubrication, and orgasm in the human female.

Parasympathetic nerve impulses from the sacral portion of the spinal cord

Sexual stimulation intensifies

Vestibular glands secrete mucus to lubricate

Orgasm—rhythmic contraction of muscles of the perineum; muscular walls of uterus and uterine tubes contract

Essentials of Human Physiology

Essentials of Human Physiology

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