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23: The Reproductive System (Female)

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    12543
  • Anatomy of the Female Reproductive System

    By the end of this section, you will be able to:

    • Describe the structure of the organs of the female reproductive system

    • Trace the path of an oocyte from ovary to fertilization

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    The female reproductive system functions to produce gametes and reproductive hormones, just like the male reproductive system; however, it also has the additional task of supporting the developing fetus and delivering it to the outside world. Unlike its male counterpart, the female reproductive system is located primarily inside the pelvic cavity (Figure 23.1). Recall that the ovaries are the female gonads. The gamete they produce is called an oocyte.

    Figure 23.1 Female Reproductive System The major organs of the female reproductive system are located inside the pelvic cavity.

    External Female Genitals

    The external female reproductive structures are referred to collectively as the vulva (Figure 23.2). The mons pubis is a pad of fat that is located at the anterior, over the pubic bone. After puberty, it becomes covered in pubic hair. The labia majora (labia = “lips”; majora = “larger”) are folds of hair-covered skin that begin just

    posterior to the mons pubis. The thinner and more pigmented labia minora (labia = “lips”; minora = “smaller”) extend medial to the labia majora. Although they naturally vary in shape and size from woman to woman, the labia minora serve to protect the female urethra and the entrance to the female reproductive tract.

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    The superior, anterior portions of the labia minora come together to encircle the clitoris (or glans clitoris), an organ that originates from the same cells as the glans penis and has abundant nerves that make it important in sexual sensation and orgasm. The hymen is a thin membrane that sometimes partially covers the entrance to the vagina. An intact hymen cannot be used as an indication of “virginity”; even at birth, this is only a partial membrane, as menstrual fluid and other secretions must be able to exit the body, regardless of penile–vaginal intercourse. The vaginal opening is located between the opening of the urethra and the anus. It is flanked by outlets to the Bartholin’s glands (or greater vestibular glands).

    Figure 23.2 The Vulva The external female genitalia are referred to collectively as the vulva. Vagina

    The vagina, shown at the bottom of Figure 23.1 and Figure 23.2, is a muscular canal (approximately 10 cm long) that serves as the entrance to the reproductive tract. It also serves as the exit from the uterus during menses and childbirth. The outer walls of the anterior and posterior vagina are formed into longitudinal columns, or ridges, and the superior portion of the vagina—called the fornix—meets the protruding uterine cervix. The walls of the vagina are lined with an outer, fibrous adventitia; a middle layer of smooth muscle; and an inner mucous membrane with transverse folds called rugae. Together, the middle and inner layers allow the expansion of the vagina to accommodate intercourse and childbirth. The thin, perforated hymen can partially surround the opening to the vaginal orifice. The hymen can be ruptured with strenuous physical exercise, penile–vaginal intercourse, and childbirth. The Bartholin’s glands and the lesser vestibular glands (located near the clitoris) secrete mucus, which keeps the vestibular area moist.

    The vagina is home to a normal population of microorganisms that help to protect against infection by pathogenic bacteria, yeast, or other organisms that can enter the vagina. In a healthy woman, the most predominant type of vaginal bacteria is from the genus Lactobacillus. This family of beneficial bacterial flora secretes lactic acid, and thus protects the vagina by maintaining an acidic pH (below 4.5). Potential pathogens are less likely to survive in these acidic conditions. Lactic acid, in combination with other vaginal secretions, makes the vagina a self- cleansing organ. However, douching—or washing out the vagina with fluid—can disrupt the normal balance of healthy microorganisms, and actually increase a woman’s risk for infections and irritation. Indeed, the American College of Obstetricians and Gynecologists recommend that women do not douche, and that they allow the vagina to maintain its normal healthy population of protective microbial flora.

    Ovaries

    The ovaries are the female gonads (see Figure 23.1). Paired ovals, they are each about 2 to 3 cm in length, about the size of an almond. The ovaries are located within the pelvic cavity, and are supported by the

    mesovarium, an extension of the peritoneum that connects the ovaries to the broad ligament. Extending from the mesovarium itself is the suspensory ligament that contains the ovarian blood and lymph vessels. Finally, the ovary itself is attached to the uterus via the ovarian ligament.

    The ovary comprises an outer covering of cuboidal epithelium called the ovarian surface epithelium that is superficial to a dense connective tissue covering called the tunica albuginea. Beneath the tunica albuginea is the cortex, or outer portion, of the organ. The cortex is composed of a tissue framework called the ovarian stroma that forms the bulk of the adult ovary. Oocytes develop within the outer layer of this stroma, each surrounded by supporting cells. This grouping of an oocyte and its supporting cells is called a follicle. The growth and development of ovarian follicles will be described shortly. Beneath the cortex lies the inner ovarian medulla, the site of blood vessels, lymph vessels, and the nerves of the ovary. You will learn more about the overall anatomy of the female reproductive system at the end of this section.

    The Uterine Tubes

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    The uterine tubes (also called fallopian tubes or oviducts) serve as the conduit of the oocyte from the ovary to the uterus (Figure 23.3). Each of the two uterine tubes is close to, but not directly connected to, the ovary and divided into sections. The isthmus is the narrow medial end of each uterine tube that is connected to the uterus. The wide distal infundibulum flares out with slender, finger-like projections called fimbriae. The middle region of the tube, called the ampulla, is where fertilization often occurs. The uterine tubes also have three layers: an outer serosa, a middle smooth muscle layer, and an inner mucosal layer. In addition to its mucus-secreting cells, the inner mucosa contains ciliated cells that beat in the direction of the uterus, producing a current that will be critical to move the oocyte.

    Figure 23.3 Ovaries, Uterine Tubes, and Uterus This anterior view shows the relationship of the ovaries, uterine tubes (oviducts), and uterus. Sperm enter through the vagina, and fertilization of an ovulated oocyte usually occurs in the distal uterine tube. From left to right, LM × 400, LM × 20. (Micrographs provided by the Regents of University of Michigan Medical School © 2012)

    The Uterus and Cervix

    The uterus is the muscular organ that nourishes and supports the growing embryo (see Figure 23.3). Its average size is approximately 5 cm wide by 7 cm long (approximately 2 in by 3 in) when a female is not pregnant. It has three sections. The portion of the uterus superior to the opening of the uterine tubes is called the fundus. The middle section of the uterus is called the body of uterus (or corpus). The cervix is the narrow inferior portion of the uterus that projects into the vagina. The cervix produces mucus secretions that become thin and stringy under the influence of high systemic plasma estrogen concentrations, and these secretions can facilitate sperm movement through the reproductive tract.

    The Breasts

    Whereas the breasts are located far from the other female reproductive organs, they are considered accessory organs of the female reproductive system. The function of the breasts is to supply milk to an infant in a process called lactation. The external features of the breast include a nipple surrounded by a pigmented areola (Figure 23.4), whose coloration may deepen during pregnancy. The areola is typically circular and can vary in size from 25 to 100 mm in diameter. The areolar region is characterized by small, raised areolar glands that secrete lubricating fluid during lactation to protect the nipple from chafing. When a baby nurses, or draws milk from the breast, the entire areolar region is taken into the mouth.

    Breast milk is produced by the mammary glands, which are modified sweat glands. The milk itself exits the breast through the nipple via 15 to 20 lactiferous ducts that open on the surface of the nipple. These lactiferous ducts each extend to a lactiferous sinus that connects to a glandular lobe within the breast itself that contains groups of milk-secreting cells in clusters called alveoli (see Figure 23.4). The clusters can change in size depending on the amount of milk in the alveolar lumen. Once milk is made in the alveoli, stimulated myoepithelial cells that surround the alveoli contract to push the milk to the lactiferous sinuses. From here, the baby can draw milk through the lactiferous ducts by suckling. The lobes themselves are surrounded by fat tissue, which determines the size of the breast; breast size differs between individuals and does not affect the amount of milk produced. Supporting the breasts are multiple bands of connective tissue called suspensory ligaments that connect the breast tissue to the dermis of the overlying skin.

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    Figure 23.4 Anatomy of the Breast During lactation, milk moves from the alveoli through the lactiferous ducts to the nipple.

    LAB 23 EXERCISES 23.1

    A

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    Label the following: Tunica albuginea * Cortex * Medulla * Ovarian ligament * Primordial follicles *

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    11

    B

    Primary follicle * Secondary follicle * Vesicular follicle * Ovulated oocyte * Corpus luteum * Corpus albicans

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    1

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    Label the following: Body * Fundus * Cervix * Fornix * Fallopian tube * Ampulla * Fimbriae * Ovary * Ovarian ligament * Endometrium * Myometrium * Perimetrium * Internal os * External os

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    C

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    Label the following: Fallopian tube * Ovary * Recto-uterine pouch * Rectum * Urinary bladder * Urethra * Clitoris * Labia minora * Labia Majora * Uterus * Vagina * Pubis Symphysis.

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    11

    D

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    E

    Label the following: Urogenital

    diaphragm * Round ligament * Infundibulum (of the fallopian tube).

    Label the following: Uterus * Fallopian tube * Round ligament * Ureter.

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    1

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    F

    Label the structures: Glans Clitoris *

    Greater vestibular gland * Skene’s

    (para-urethral) glands * Urethral orifice.

    G

    2

    1

    9

    Label the following: FSH * LH * Estrogen (E2) * Progesterone (P) * Follicular phase * Luteal phase * Menstrual phase * Proliferative phase * Secretory phase * Ovulation.

    320

    2

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    H

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    Day 0 14 28

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    Label the following: Lobe * Lactiferous ducts * Suspensory ligaments *

    Lactiferous sinus * Pectoralis minor * Pectoralis major * Intercostal muscles

    * Fascia * Adipose tissue.

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    MODELS: Female Hemi-Pelvises, Torso, Breast and Ovary

     Fallopian Tubes (uterine tubes)

    • Ampulla

    • Fimbriae

    • Infundibulum

    • Isthmus

       Uterus

    • Fundus

    • Body

    • Cervix

    • Cervical os (internal & external)

    • Endometrium

    • myometrium

    • Perimetrium

    • Round ligament

       Vagina

    • Rugae

    • Fornix

       Vulva

    • Mons pubis

    • Vestibule

    • Urethral orifice

    • Labia minora

    • Labia majora

       Clitoris

    • Glans clitoris

    • Clitoral hood

       Ovary (model)

    • Primordial * Primary * Secondary * Vesicular/Graafian follicles

    • Corpus luteum

    • Corpus albicans

    • Ovarian ligament

    • Suspensory ligament (of the ovary)

       Recto-vaginal (recto-uterine) pouch

       Breast (Mammary Glands)

    • Areola

    • Nipple

    • Lobe

    • Lactiferous duct

    • Lactiferous sinus

    • Adipose tissue

    • Pectoralis major muscle

    • Suspensory (Cooper’s) ligaments

      Histology:

       Ovary

    • Follicles: graafian (secretory) * secondary * primary.

    • corpus luteum

    • corpus albicans

    • oocyte

    • follicular cells

    • antrum

       Uterus

    • Endometrium & myometrium

       Fallopian tubes

    • Mucosa * Muscularis * Lumen