Female Reproductive System

1. Female Reproductive System Overview

The female, or ovarian, 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, most of the female reproductive system is located inside the pelvic cavity, although there are also external female reproductive structures. Here, we will look at both the external and internal structures of the female reproductive system.

2. External Female Reproductive Structures

Although the majority of the female reproductive system is internal, the external components also serve important functions in reproduction.

2a. External Female Genitals

The lower external female reproductive structures (genitalia, or genitals) are referred to collectively as the vulva. 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 toward the middle of the labia majora. Although they naturally vary in shape and size from person to person, the labia minora help protect the urethra and the entrance to the reproductive tract.

The superior, anterior portions of the labia minora come together to encircle the glans clitoris, an organ that originates from the same cells as the glans penis in males and has abundant nerves that make it important in sexual sensation and orgasm. The clitoris is covered by a layer of skin called the prepuce.

Although we may think of the clitoris as being an external structure, most of the components are actually internal.

key concept

The overall size of the clitoris is approximately 9–11 cm when not in a state of arousal. Of that, the glans clitoris is approximately 2–2.5 cm, and the rest of the clitoris is internal.

The vaginal opening is located between the opening of the urethra and the anus. It is flanked by outlets to the greater vestibular glands (or Bartholin’s glands). There are also two vestibular bulbs (or bulbs of vestibule), which are formed from corpus spongiosum tissue; these are bulbs of erectile tissue that are close to the body of the clitoris and engorge with blood during sexual arousal. The corpora cavernosa (singular = corpus cavernosum) are two cylindrical erectile chambers of the clitoris that also fill with blood to become erect during sexual arousal.

The hymen is a thin membrane that sometimes partially covers the entrance to the vagina.

did you know

Some people believe that a torn hymen is an indication of if a female is a “virgin” (has not had penile–vaginal intercourse). However, an intact hymen cannot be used as an indication of “virginity.” Even at birth, this is only a partial membrane because menstrual fluid and other secretions must be able to exit the body, regardless of penile–vaginal intercourse.

terms to know

Vulva

The external female genitalia.

Mons Pubis

The mound of fatty tissue located at the front of the vulva.

Labia Majora

The hair-covered folds of skin located behind the mons pubis.

Labia Minora

Thin, pigmented, hairless flaps of skin located medial and deep to the labia majora.

Clitoris

The nerve-rich area of the vulva that contributes to sexual sensation during intercourse (also, glans clitoris).

Greater Vestibular Glands

Glands that produce a thick mucus that maintains moisture in the vulva area (also, Bartholin’s glands).

Vestibular Bulb

One of two bulbs of erectile tissue close to the clitoris that become engorged with blood during sexual arousal.

Hymen

A piece of tissue that can cover part of the vaginal opening.

2b. The Breasts

The breasts are located far from the other female reproductive organs, and they are therefore 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, 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 (of the breast). 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.

During the normal hormonal fluctuations in the uterine cycle (also known as the menstrual cycle), breast tissue responds to changing levels of estrogen and progesterone, which can lead to swelling and breast tenderness in some individuals, especially during the secretory phase. If pregnancy occurs, the increase in hormones leads to further development of the mammary tissue and enlargement of the breasts.

terms to know

Areola

The highly pigmented, circular area surrounding the raised nipple and containing areolar glands that secrete fluid important for lubrication during suckling.

Mammary Glands

Modified sweat glands inside the breast that secrete milk.

Lactiferous Ducts

Ducts that connect the mammary glands to the nipple and allow for the transport of milk.

Alveoli (of the Breast)

Milk-secreting cells in the mammary gland.

3. Internal Female Reproductive Structures

As you learned earlier in the lesson, the major organs of the female reproductive system are located within the pelvic cavity. These are the organs that are primarily responsible for reproduction.

3a. The Vagina

The vagina, shown at the bottom of the image above, 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 (the approximately monthly shedding of the inner portion of the endometrium through the vagina, which you will learn more about in a future lesson) 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 connective tissue; a middle layer of smooth muscle; and an inner mucous membrane with transverse folds called rugae. Recall that you previously learned that rugae (ruga is singular, rugae is plural) are folds of tissue. 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 greater vestibular 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 person, 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.

key concept

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 the risk for infections and irritation. Indeed, the American College of Obstetricians and Gynecologists recommend that people do not douche and that they allow the vagina to maintain its normal healthy population of protective microbial flora.

term to know

Vagina

A tunnel-like organ that provides access to the uterus for the insertion of semen and from the uterus for the birth of a baby.

3b. The Uterus and Cervix

The uterus is the muscular organ that nourishes and supports a growing embryo (see the image above). 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 the uterus (or corpus).

Several ligaments help maintain the position of the uterus within the abdominopelvic cavity. The broad ligament is a fold of peritoneum that serves as a primary support for the uterus, extending laterally from both sides of the uterus and attaching it to the pelvic wall. The round ligament attaches to the uterus near the uterine tubes and extends to the labia majora. Finally, the uterosacral ligament stabilizes the uterus posteriorly by its connection from the cervix to the pelvic wall.

IN CONTEXT

Uterine Prolapse

A potential issue that can affect the uterus is uterine prolapse. The pelvic floor is a group of muscles, ligaments, and connective tissues that support the pelvic organs, including the uterus. Uterine prolapse occurs when the pelvic floor can no longer support the uterus; the uterus will relax from its normal position and bulge into the vagina. Although not life-threatening, this condition can cause pain and other functional difficulties. Symptoms of uterine prolapse include urinary incontinence, feeling of fullness in the vagina, bulging of the vagina, constipation, and back pain.

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.

terms to know

Uterus

The muscular hollow organ in which a fertilized egg develops into a fetus.

Cervix

The elongate inferior end of the uterus where it connects to the vagina.

3c. The Uterine Tubes

The uterine tubes (also called fallopian tubes or oviducts) serve as the conduit of the oocyte from the ovary to the uterus. 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 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.

Following ovulation, the oocyte, surrounded by a few granulosa cells, is released into the peritoneal cavity. The fimbriae of the nearby uterine tube, either left or right, catches the oocyte and sweeps it into the uterine tube.

key concept

Unlike sperm, oocytes cannot move on their own because they lack flagella (the hair-like structures that propel sperm). So, how do they travel into the uterine tube and toward the uterus?

High concentrations of estrogen that occur around the time of ovulation induce contractions of the smooth muscle along the length of the uterine tube. These contractions occur every 4 to 8 seconds, and the result is a coordinated movement that sweeps the surface of the ovary and the pelvic cavity. Current flowing toward the uterus is generated by coordinated beating of the cilia (short, hair-like structures) that line the outside and lumen of the length of the uterine tube. These cilia beat more strongly in response to the high estrogen concentrations that occur around the time of ovulation. As a result of these mechanisms, the oocyte-granulosa cell complex is pulled into the interior of the tube. Once inside, the muscular contractions and beating cilia move the oocyte slowly toward the uterus. When fertilization does occur, sperm typically meet the egg while it is still moving through the ampulla.

If the oocyte is successfully fertilized, the resulting zygote will begin to divide into two cells, then four, and so on, as it makes its way through the uterine tube and into the uterus. There, it will implant and continue to grow. If the egg is not fertilized, it will simply degrade—either in the uterine tube or in the uterus, where it may be shed with the next menstrual period.

The open-ended structure of the uterine tubes can have significant health consequences if bacteria or other contagions enter through the vagina and move through the uterus, into the tubes, and then into the pelvic cavity. If this is left unchecked, a bacterial infection (sepsis) could quickly become life-threatening. The spread of an infection in this manner is of special concern when unskilled practitioners perform abortions (voluntary pregnancy termination) in non-sterile conditions. Sepsis is also associated with sexually transmitted bacterial infections, especially gonorrhea and chlamydia, which you will learn more about in a future lesson. These increase a person's risk for pelvic inflammatory disease (PID), which is an infection of the uterine tubes or other reproductive organs. Even when resolved, PID can leave scar tissue in the tubes, leading to infertility.

terms to know

Uterine Tubes

Ducts that facilitate transport of an ovulated oocyte to the uterus (also, fallopian tubes or oviducts).

Fimbriae

Finger-like projections on the lateral end of each uterine tube that catch the oocyte and sweep it into the uterine tube.

3d. The Ovaries

Recall that the ovaries are the female gonads. They produce oocytes as well as substances such as the sex steroid hormones estrogen and progesterone. 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. Beneath the cortex lies the inner ovarian medulla, which is the site of blood vessels, lymph vessels, and the nerves of the ovary.

term to know

Ovaries

Female gonads that produce oocytes and sex steroid hormones (notably estrogen and progesterone).

SOURCE: THIS TUTORIAL HAS BEEN ADAPTED FROM OPENSTAX “ANATOMY AND PHYSIOLOGY 2E”. ACCESS FOR FREE AT OPENSTAX.ORG/BOOKS/ANATOMY-AND-PHYSIOLOGY-2E/PAGES/1-INTRODUCTION. LICENSE: CREATIVE COMMONS ATTRIBUTION 4.0 INTERNATIONAL.