What is the entrance to the uterus?

Female Anatomy: The Reproductive Organs

In male and female anatomy, many bodily functions are similar.

The circulatory system and digestive system, for example, function in much the same ways in both male and female bodies.

The biggest differences between male and female anatomy are in the reproductive system. The female sexual anatomy and its composite parts allow women to become pregnant and bear children.

While the reproductive organs in the female anatomy perform their own specific functions, they also work together as a highly complex, interrelated system.

The female sexual anatomy is comprised of both internal and external parts.

Female Sexual Anatomy: Internal Organs

Key organs for female reproduction are protectively located deep within the body. These include:

  • Ovaries — A woman normally has a pair of ovaries that resemble almonds in size and shape. They are home to the female sex cells, called eggs, and they also produce estrogen, the female sex hormone. Women’s ovaries already contain several hundred thousand undeveloped eggs at birth, but the eggs are not called into action until puberty. Roughly once a month, starting at puberty and lasting until menopause, the ovaries release an egg into the fallopian tubes; this is called ovulation. When fertilization does not occur, the egg leaves the body as part of the menstrual cycle.
  • Fallopian tubes — The ovaries connect to the uterus via the fallopian tubes. Fertilization usually happens within the fallopian tubes. Then, the fertilized egg makes its way down to the uterus.
  • Uterus — The uterus is located in the pelvis of a woman’s body and is made up of smooth muscle tissue. Commonly referred to as the womb, the uterus is hollow and holds the fetus during pregnancy. Each month, the uterus develops a lining that is rich in nutrients. The reproductive purpose of this lining is to provide nourishment for a developing fetus. Since eggs aren’t usually fertilized, the lining usually leaves the body as menstrual blood during a woman’s monthly period.
  • Cervix — The lower part of the uterus, which connects to the vagina, is known as the cervix. Often called the neck or entrance to the womb, the cervix lets menstrual blood out and semen into the uterus. The cervix remains closed during pregnancy but can expand dramatically during childbirth.
  • Vagina — The vagina has both internal and external parts and connects the uterus to the outside of the body. Made up of muscle and skin, the vagina is a long hollow tube that is sometimes called the “birth canal” because, if you are pregnant, the vagina is the pathway the baby will take when it’s ready to be born. The vagina also allows menstrual blood to leave a woman’s body during reproduction and is where the penis deposits semen during sexual intercourse.

Female Sexual Anatomy: External Parts

The entrance to the vagina is surrounded by external parts that generally serve to protect the internal organs; this area is called the vulva. The vulva consists of the following:

  • Labia majora — Translated as “large lips,” this flap of skin protects the vagina from foreign particles.
  • Labia minora — The “small lips” also surround and protect the vaginal opening and are located inside the labia majora.
  • Clitoris — The clitoris is a sensitive organ located above the vaginal opening. The clitoris does not directly affect reproduction, but it is an important part of the female sexual anatomy; many women need clitoral stimulation to orgasm.
  • Mons pubis — The fatty mound of tissue that covers the pubic bone. Often called the “mons.”
  • Perineum — A stretch of hairless, sensitive skin that extends from the bottom of the vaginal opening back to the anus.

Female reproductive organs

The female reproductive organs include the ovaries, fallopian tubes, uterus and vagina.

Front view of female reproductive organs

Side view of female reproductive organs

Ovaries

The ovaries are the main reproductive organs of a woman. The two ovaries, which are about the size and shape of almonds, produce female hormones (oestrogens and progesterone) and eggs (ova). All the other female reproductive organs are there to transport, nurture and otherwise meet the needs of the egg or developing fetus.

The ovaries are held in place by various ligaments which anchor them to the uterus and the pelvis. The ovary contains ovarian follicles, in which eggs develop. Once a follicle is mature, it ruptures and the developing egg is ejected from the ovary into the fallopian tubes. This is called ovulation. Ovulation occurs in the middle of the menstrual cycle and usually takes place every 28 days or so in a mature female. It takes place from either the right or left ovary at random.

Fallopian tubes

The fallopian tubes are about 10 cm long and begin as funnel-shaped passages next to the ovary. They have a number of finger-like projections known as fimbriae on the end near the ovary. When an egg is released by the ovary it is ‘caught’ by one of the fimbriae and transported along the fallopian tube to the uterus. The egg is moved along the fallopian tube by the wafting action of cilia — hairy projections on the surfaces of cells at the entrance of the fallopian tube — and the contractions made by the tube. It takes the egg about 5 days to reach the uterus and it is on this journey down the fallopian tube that fertilisation may occur if a sperm penetrates and fuses with the egg. The egg, however, is usually viable for only 24 hours after ovulation, so fertilisation usually occurs in the top one-third of the fallopian tube.

Uterus

The uterus is a hollow cavity about the size of a pear (in women who have never been pregnant) that exists to house a developing fertilised egg. The main part of the uterus (which sits in the pelvic cavity) is called the body of the uterus, while the rounded region above the entrance of the fallopian tubes is the fundus and its narrow outlet, which protrudes into the vagina, is the cervix.

The thick wall of the uterus is composed of 3 layers. The inner layer is known as the endometrium. If an egg has been fertilised it will burrow into the endometrium, where it will stay for the rest of its growth. The uterus will expand during a pregnancy to make room for the growing fetus. A part of the wall of the fertilised egg, which has burrowed into the endometrium, develops into the placenta. If an egg has not been fertilised, the endometrial lining is shed at the end of each menstrual cycle.

The myometrium is the large middle layer of the uterus, which is made up of interlocking groups of muscle. It plays an important role during the birth of a baby, contracting rhythmically to move the baby out of the body via the birth canal (vagina).

Vagina

The vagina is a fibromuscular tube that extends from the cervix to the vestibule of the vulva. The vagina receives the penis and semen during sexual intercourse and also provides a passageway for menstrual blood flow to leave the body.

Bookshelf

What jobs do the internal sex organs do?

The main jobs of the internal female sex organs are to enable pregnancy and childbirth. The internal sex organs include:

  • Ovaries
  • Fallopian tubes
  • Uterus (womb)
  • Cervix
  • Vagina

    Internal female sex organs, front view

The two ovaries are the female reproductive glands (gonads). They are located on the right and left sides of the abdomen, and contain the eggs. These eggs can be fertilized by male sperm. The ovaries also produce important female sex hormones such as estrogen and progesterone, which – among other things – regulate the menstrual cycle.

The fallopian tubes connect the ovaries to the uterus: During ovulation, one of the ovaries releases a mature egg into the funnel-shaped entrance of the fallopian tube. The egg then travels through the fallopian tube to the uterus. After sex, the egg can already be reached and fertilized by a sperm cell in the fallopian tube.

The uterus (womb) is roughly pear-shaped, and held in place in the pelvis by ligaments and muscles. The two fallopian tubes enter the upper, rounded end of the uterus on the right and the left. The lower part of the uterus is somewhat narrower, resembling the neck of a bottle. This section is called the cervix. The very bottom end of the cervix bulges into the vagina a little, at the opening of the cervix. On the infertile days of the menstrual cycle, the opening of the cervix is closed by thick mucus.

The inside of the uterus is lined with special membranes called the endometrium. In each menstrual cycle, female sex hormones stimulate the endometrium to grow into a thick layer with higher blood flow so it is prepared for a fertilized egg: The egg can then become implanted in the lining of the uterus and grow into an embryo. If fertilization doesn’t take place, the thick membrane tissue which has built up is shed and leaves the woman’s body during her period.

During pregnancy, the uterus stretches to accommodate the growing baby. Shortly before and during childbirth, the uterine muscles repeatedly contract strongly. These contractions help to push the baby outwards through the vagina.

The vagina connects the internal and external sex organs. It receives the penis during sexual intercourse. At its upper end, the cervix provides an entrance for male sperm cells to reach the uterus – and during childbirth, it’s the passageway for the baby.

Female Reproductive Organ Anatomy

External Genitalia

The vulva, also known as the pudendum, is a term used to describe those external organs that may be visible in the perineal area (see the images below). The vulva consists of the following organs: mons pubis, labia minora and majora, hymen, clitoris, vestibule, urethra, Skene glands, greater vestibular (Bartholin) glands, and vestibular bulbs. The boundaries include the mons pubis anteriorly, the rectum posteriorly, and the genitocrural folds (thigh folds) laterally.

External female genitalia.Deeper view of external structures.

Mons pubis

The mons pubis is the rounded portion of the vulva where sexual hair development occurs at the time of puberty. This area may be described as directly anterosuperior to the pubic symphysis.

Labia

The labia majora are 2 large, longitudinal folds of adipose and fibrous tissue. They vary in size and distribution from female to female, and the size is dependent upon adipose content. They extend from the mons anteriorly to the perineal body posteriorly. The labia majora have hair follicles.

The labia minora, also known as nymphae, are 2 small cutaneous folds that are found between the labia majora and the introitus or vaginal vestibule. Anteriorly, the labia minora join to form the frenulum of the clitoris.

Hymen

The hymen is a thin membrane found at the entrance to the vaginal orifice. Often, this membrane is perforated before the onset of menstruation, allowing flow of menses. The hymen varies greatly in shape.

Clitoris

The clitoris is an erectile structure found beneath the anterior joining of the labia minora. Its width in an adult female is approximately 1 cm, with an average length of 1.5–2.0 cm. The clitoris is made up of 2 crura, which attach to the periosteum of the ischiopubic rami. It is a very sensitive structure, analogous to the male penis. It is innervated by the dorsal nerve of the clitoris, a terminal branch of the pudendal nerve.

Vestibule and urethra

Between the clitoris and the vaginal introitus (opening) is a triangular area known as the vestibule, which extends to the posterior fourchette. The vestibule is where the urethral (urinary) meatus is found, approximately 1 cm anterior to the vaginal orifice, and it also gives rise to the opening of the Skene glands bilaterally. The urethra is composed of membranous connective tissue and links the urinary bladder to the vestibule externally. A female urethra ranges in length from 3.5 to 5.0 cm.

Skene and Bartholin glands

The Skene glands secrete lubrication at the opening of the urethra. The greater vestibular (Bartholin) glands are also responsible for secreting lubrication to the vagina, with openings just outside the hymen, bilaterally, at the posterior aspect of the vagina. Each gland is small, similar in shape to a kidney bean.

Vestibular bulbs

Finally, the vestibular bulbs are 2 masses of erectile tissue that lie deep to the bulbocavernosus muscles bilaterally.

Internal Genitalia

Vagina

The vagina extends from the vulva externally to the uterine cervix internally. It is located within the pelvis, anterior to the rectum and posterior to the urinary bladder. The vagina lies at a 90º angle in relation to the uterus. The vagina is held in place by endopelvic fascia and ligaments (see the image below).

Superior view of pelvic organs.

The vagina is lined by rugae, which are situated in folds throughout. These allow easy distention, especially during child bearing. The structure of the vagina is a network of connective, membranous, and erectile tissues.

The pelvic diaphragm, the sphincter urethrae and transverse peroneus muscles, and the perineal membrane support the vagina. The sphincter urethrae and the transverse peroneus are innervated by perineal branches of the pudendal nerve. The pelvic diaphragm primarily refers to the levator ani and the coccygeus and is innervated by branches of sacral nerves S2-S4.

The vascular supply to the vagina is primarily from the vaginal artery, a branch of the anterior division of the internal iliac artery. Several of these arteries may be found on either side of the pelvis to richly supply the vagina.

The nerve supply to the vagina is primarily from the autonomic nervous system. Sensory fibers to the lower vagina arise from the pudendal nerve, and pain fibers are from sacral nerve roots. Lymphatic drainage of the vagina is generally to the external iliac nodes (upper third of the vagina), the common and internal iliac nodes (middle third), and the superficial inguinal nodes (lower third).

Uterus

The uterus is the inverted pear-shaped female reproductive organ that lies in the midline of the body, within the pelvis between the bladder and the rectum. It is thick-walled and muscular, with a lining that, during reproductive years, changes in response to hormone stimulation throughout a woman’s monthly cycle.

The uterus can be divided into 2 parts: the most inferior aspect is the cervix, and the bulk of the organ is called the body of the uterus (corpus uteri). Between these 2 is the isthmus, a short area of constriction.

The body of the uterus is globe-shaped and is typically situated in an anteverted position, at a 90º angle to the vagina. The upper aspect of the body is dome-shaped and is called the fundus; it is typically the most muscular part of the uterus. The body of the uterus is responsible for holding a pregnancy, and strong uterine wall contractions help to expel the fetus during labor and delivery.

The average weight of a nonpregnant, nulliparous uterus is approximately 40-50 g. A multiparous uterus may weigh slightly more than this, with an upper limit of approximately 110 g. A menopausal uterus is small and atrophied and typically weighs much less.

The cavity of the uterus is flattened and triangular. The uterine tubes enter the uterine cavity bilaterally in the superolateral portion of the cavity.

The uterus is connected to its surrounding structures by a series of ligaments and connective tissue. The pelvic peritoneum is attached to the body and the cervix as the broad ligament, reflecting onto the bladder. The broad ligament attaches the uterus to the lateral pelvic side walls. Within the broad base of the broad ligament, between its anterior and posterior laminae, connective tissue strands associated with the uterine and vaginal vessels help to support the uterus and vagina. Together, these strands are referred to as the cardinal ligament.

Rectouterine ligaments, lying within peritoneal folds, stretch posteriorly from the cervix to reach the sacrum. The round ligaments of the uterus are much denser structures and connect the uterus to the anterolateral abdominal wall at the deep inguinal ring. They lie within the anterior lamina of the broad ligament. Within the round ligament is the artery of Sampson, a small artery that must be ligated during hysterectomy.

The vasculature of the uterus is derived from the uterine arteries and veins. The uterine vessels arise from the anterior division of the internal iliac, and branches of the uterine artery anastomose with the ovarian artery along the uterine tube.

The nerve supply and lymphatic drainage of the uterus are complex. Lymphatic drainage is primarily to the lateral aortic, pelvic, and iliac nodes that surround the iliac vessels. The nerve supply is attained through the sympathetic nervous system (by way of the hypogastric and ovarian plexuses) and the parasympathetic nervous system (by way of the pelvic splanchnic nerves from the second through fourth sacral nerves).

Cervix

The cervix is the inferior portion of the uterus, separating the body of the uterus from the vagina. The cervix is cylindrical in shape, with an endocervical canal located in the midline, allowing passage of semen into the uterus. The external opening into the vagina is termed the external os, and the internal opening into the endometrial cavity is termed the internal os. The internal os is the portion of a female cervix that dilates to allow delivery of the fetus during labor. The average length of the cervix is 3-5 cm.

The vasculature is supplied by descending branches of the uterine artery, which run bilaterally at the 3 o’clock and 9 o’clock position of the cervix. The nerve supply to the cervix is via the parasympathetic nervous system by way of the second through fourth sacral segments. Many pain nerve fibers run alongside these parasympathetics. Lymphatic drainage of the cervix is complex. The obturator, common iliac, internal iliac, external iliac, and visceral parametrial nodes are the main drainage points.

Uterine tubes

The uterine tubes (also referred to as oviducts or fallopian tubes) are uterine appendages located bilaterally at the superior portion of the cavity. Their primary function is to transport sperm toward the egg, which is released by the ovary, and then to allow passage of the fertilized egg back to the uterus for implantation.

The uterine tubes exit the uterus through an area known as the cornua and form a connection between the endometrial and peritoneal cavities. Each tube is approximately 10 cm in length and 1 cm in diameter and is situated within a portion of the broad ligament called the mesosalpinx. The distal portion of the uterine tube ends in an orientation encircling the ovary.

The uterine tube has 3 parts. The first segment, closest to the uterus, is called the isthmus. The second segment is the ampulla, which becomes more dilated in diameter and is the typical place of fertilization. The final segment, furthest from the uterus, is the infundibulum. The infundibulum gives rise to the fimbriae, fingerlike projections that are responsible for catching the egg that is released by the ovary.

The arterial supply to the uterine tubes is from branches of the uterine and ovarian arteries, small vessels that are located within the mesosalpinx. The nerve supply to the uterine tubes is via both sympathetic and parasympathetic fibers. Sensory fibers run from thoracic segments 11-12 and lumbar segment 1. Lymphatic drainage of the uterine tubes is through the iliac and aortic nodes.

Ovaries

The ovaries are paired organs located on either side of the uterus within the mesovarium portion of the broad ligament below the uterine tubes. The ovaries are responsible for housing and releasing the ova, or eggs, necessary for reproduction. At birth, a female has approximately 1-2 million eggs, but only 300 of these eggs ever mature and are released for the purpose of fertilization.

The ovaries are small and oval-shaped, exhibit a grayish color, and have an uneven surface. The actual size of an ovary depends on a woman’s age and hormonal status; the ovaries are approximately 3-5 cm in length during childbearing years and become much smaller and atrophic once menopause occurs. A cross-section of the ovary reveals many cystic structures that vary in size. These structures represent ovarian follicles at different stages of development and degeneration.

Several ligaments support the ovary. The ovarian ligament connects the uterus and ovary. The posterior portion of the broad ligament forms the mesovarium, which supports the ovary and houses the vascular supply. The suspensory ligament of the ovary (infundibular pelvic ligament), a peritoneal fold overlying the ovarian vessels, attaches the ovary to the pelvic side wall.

Blood supply to the ovary is via the ovarian artery; both right and left ovarian arteries originate directly from the descending aorta at the level of the L2 vertebra. The ovarian artery and vein enter and exit the ovary at the hilum. The left ovarian vein drains into the left renal vein, and the right ovarian vein empties directly into the inferior vena cava.

Nerve supply to the ovaries run with the vasculature within the suspensory ligament of the ovary, entering the ovary at the hilum. Supply is through the ovarian, hypogastric, and aortic plexuses. Lymphatic drainage of the ovary is primarily to the lateral aortic nodes; however, the iliac nodes may also be involved.

Female Reproductive System

How does the female reproductive system work?

The female reproductive system provides several functions. The ovaries produce the egg cells, called the ova or oocytes. The oocytes are then transported to the fallopian tube where fertilization by a sperm may occur. The fertilized egg then moves to the uterus, where the uterine lining has thickened in response to the normal hormones of the reproductive cycle. Once in the uterus, the fertilized egg can implant into thickened uterine lining and continue to develop. If implantation does not take place, the uterine lining is shed as menstrual flow. In addition, the female reproductive system produces female sex hormones that maintain the reproductive cycle.

During menopause, the female reproductive system gradually stops making the female hormones necessary for the reproductive cycle to work. At this point, menstrual cycles can become irregular and eventually stop. One year after menstrual cycles stop, the woman is considered to be menopausal.

What parts make-up the female anatomy?

The female reproductive anatomy includes both external and internal structures.

The function of the external female reproductive structures (the genital) is twofold: To enable sperm to enter the body and to protect the internal genital organs from infectious organisms.

The main external structures of the female reproductive system include:

  • Labia majora: The labia majora (“large lips”) enclose and protect the other external reproductive organs. During puberty, hair growth occurs on the skin of the labia majora, which also contain sweat and oil-secreting glands.
  • Labia minora: The labia minora (“small lips”) can have a variety of sizes and shapes. They lie just inside the labia majora, and surround the openings to the vagina (the canal that joins the lower part of the uterus to the outside of the body) and urethra (the tube that carries urine from the bladder to the outside of the body). This skin is very delicate and can become easily irritated and swollen.
  • Bartholin’s glands: These glands are located next to the vaginal opening on each side and produce a fluid (mucus) secretion.
  • Clitoris: The two labia minora meet at the clitoris, a small, sensitive protrusion that is comparable to the penis in males. The clitoris is covered by a fold of skin, called the prepuce, which is similar to the foreskin at the end of the penis. Like the penis, the clitoris is very sensitive to stimulation and can become erect.

The internal reproductive organs include:

  • Vagina: The vagina is a canal that joins the cervix (the lower part of uterus) to the outside of the body. It also is known as the birth canal.
  • Uterus (womb): The uterus is a hollow, pear-shaped organ that is the home to a developing fetus. The uterus is divided into two parts: the cervix, which is the lower part that opens into the vagina, and the main body of the uterus, called the corpus. The corpus can easily expand to hold a developing baby. A canal through the cervix allows sperm to enter and menstrual blood to exit.
  • Ovaries: The ovaries are small, oval-shaped glands that are located on either side of the uterus. The ovaries produce eggs and hormones.
  • Fallopian tubes: These are narrow tubes that are attached to the upper part of the uterus and serve as pathways for the ova (egg cells) to travel from the ovaries to the uterus. Fertilization of an egg by a sperm normally occurs in the fallopian tubes. The fertilized egg then moves to the uterus, where it implants to the uterine lining.

What happens during the menstrual cycle?

Females of reproductive age (beginning anywhere from 11 to 16 years of age) experience cycles of hormonal activity that repeat at about one-month intervals. Menstru means “monthly” – leading to the term menstrual cycle. With every cycle, a woman’s body prepares for a potential pregnancy, whether or not that is the woman’s intention. The term menstruation refers to the periodic shedding of the uterine lining. Many women call the days that they notice vaginal bleeding their “period,” “menstrual” or cycle.

The average menstrual cycle takes about 28 days and occurs in phases. These phases include:

  • The follicular phase (development of the egg)
  • The ovulatory phase (release of the egg)
  • The luteal phase (hormone levels decrease if the egg does not implant)

There are four major hormones (chemicals that stimulate or regulate the activity of cells or organs) involved in the menstrual cycle. These hormones include:

  • Follicle-stimulating hormone
  • Luteinizing hormone
  • Estrogen
  • Progesterone

Follicular phase

This phase starts on the first day of your period. During the follicular phase of the menstrual cycle, the following events occur:

  • Two hormones, follicle stimulating hormone (FSH) and luteinizing hormone (LH) are released from the brain and travel in the blood to the ovaries.
  • The hormones stimulate the growth of about 15 to 20 eggs in the ovaries, each in its own “shell,” called a follicle.
  • These hormones (FSH and LH) also trigger an increase in the production of the female hormone estrogen.
  • As estrogen levels rise, like a switch, it turns off the production of follicle-stimulating hormone. This careful balance of hormones allows the body to limit the number of follicles that will prepare eggs to be released.
  • As the follicular phase progresses, one follicle in one ovary becomes dominant and continues to mature. This dominant follicle suppresses all of the other follicles in the group. As a result, they stop growing and die. The dominant follicle continues to produce estrogen.

Ovulatory phase

The ovulatory phase (ovulation) usually starts about 14 days after the follicular phase started, but this can vary. The ovulatory phase falls between the follicular phase and luteal phase. Most women will have a menstrual period 10 to 16 days after ovulation. During this phase, the following events occur:

  • The rise in estrogen from the dominant follicle triggers a surge in the amount of luteinizing hormone that is produced by the brain.
  • This causes the dominant follicle to release its egg from the ovary.
  • As the egg is released (a process called ovulation) it is captured by finger-like projections on the end of the fallopian tubes (fimbriae). The fimbriae sweep the egg into the tube.
  • For one to five days prior to ovulation, many women will notice an increase in egg white cervical mucus. This mucus is the vaginal discharge that helps to capture and nourish sperm on its way to meet the egg for fertilization.

Luteal phase

The luteal phase begins right after ovulation and involves the following processes:

  • Once it releases its egg, the empty ovarian follicle develops into a new structure called the corpus luteum.
  • The corpus luteum secretes the hormones estrogen and progesterone. Progesterone prepares the uterus for a fertilized egg to implant.
  • If intercourse has taken place and a man’s sperm has fertilized the egg (a process called conception), the fertilized egg (embryo) will travel through the fallopian tube to implant in the uterus. The woman is now considered pregnant.
  • If the egg is not fertilized, it passes through the uterus. Not needed to support a pregnancy, the lining of the uterus breaks down and sheds, and the next menstrual period begins.

How many eggs does a woman have?

During fetal life, there are about 6 million to 7 million eggs. From this time, no new eggs are produced. At birth, there are approximately 1 million eggs; and by the time of puberty, only about 300,000 remain. Of these, only 300 to 400 will be ovulated during a woman’s reproductive lifetime. Fertility can drop as a woman ages due to decreasing number and quality of the remaining eggs.

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Female Reproductive System

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What Is Reproduction?

Reproduction is the process by which organisms make more organisms like themselves. But even though the reproductive system is essential to keeping a species alive, unlike other body systems, it’s not essential to keeping an individual alive.

In the human reproductive process, two kinds of sex cells, or gametes (GAH-meetz), are involved. The male gamete, or sperm, and the female gamete, the egg or ovum, meet in the female’s reproductive system. When sperm fertilizes (meets) an egg, this fertilized egg is called a zygote (pronounced: ZYE-goat). The zygote goes through a process of becoming an embryo and developing into a fetus.

The male reproductive system and the female reproductive system both are needed for reproduction.

Humans, like other organisms, pass some characteristics of themselves to the next generation. We do this through our genes, the special carriers of human traits. The genes that parents pass along are what make their children similar to others in their family, but also what make each child unique. These genes come from the male’s sperm and the female’s egg.

What Is the Female Reproductive System?

The external part of the female reproductive organs is called the vulva, which means covering. Located between the legs, the vulva covers the opening to the vagina and other reproductive organs inside the body.

The fleshy area located just above the top of the vaginal opening is called the mons pubis. Two pairs of skin flaps called the labia (which means lips) surround the vaginal opening. The clitoris, a small sensory organ, is located toward the front of the vulva where the folds of the labia join. Between the labia are openings to the urethra (the canal that carries pee from the bladder to the outside of the body) and vagina. When girls become sexually mature, the outer labia and the mons pubis are covered by pubic hair.

A female’s internal reproductive organs are the vagina, uterus, fallopian tubes, and ovaries.

The vagina is a muscular, hollow tube that extends from the vaginal opening to the uterus. Because it has muscular walls, the vagina can expand and contract. This ability to become wider or narrower allows the vagina to accommodate something as slim as a tampon and as wide as a baby. The vagina’s muscular walls are lined with mucous membranes, which keep it protected and moist.

The vagina serves three purposes:

  1. It’s where the penis is inserted during sexual intercourse.
  2. It’s the pathway (the birth canal) through which a baby leaves a woman’s body during childbirth.
  3. It’s the route through which menstrual blood leaves the body during periods.

A very thin piece of skin-like tissue called the hymen partly covers the opening of the vagina. Hymens are often different from female to female. Most women find their hymens have stretched or torn after their first sexual experience, and the hymen may bleed a little (this usually causes little, if any, pain). Some women who have had sex don’t have much of a change in their hymens, though. And some women’s hymens have already stretched even before they have sex.

The vagina connects with the uterus, or womb, at the cervix (which means neck). The cervix has strong, thick walls. The opening of the cervix is very small (no wider than a straw), which is why a tampon can never get lost inside a girl’s body. During childbirth, the cervix can expand to allow a baby to pass.

The uterus is shaped like an upside-down pear, with a thick lining and muscular walls — in fact, the uterus contains some of the strongest muscles in the female body. These muscles are able to expand and contract to accommodate a growing fetus and then help push the baby out during labor. When a woman isn’t pregnant, the uterus is only about 3 inches (7.5 centimeters) long and 2 inches (5 centimeters) wide.

At the upper corners of the uterus, the fallopian tubes connect the uterus to the ovaries. The ovaries are two oval-shaped organs that lie to the upper right and left of the uterus. They produce, store, and release eggs into the fallopian tubes in the process called ovulation (pronounced: av-yoo-LAY-shun).

There are two fallopian (pronounced: fuh-LO-pee-un) tubes, each attached to a side of the uterus. Within each tube is a tiny passageway no wider than a sewing needle. At the other end of each fallopian tube is a fringed area that looks like a funnel. This fringed area wraps around the ovary but doesn’t completely attach to it. When an egg pops out of an ovary, it enters the fallopian tube. Once the egg is in the fallopian tube, tiny hairs in the tube’s lining help push it down the narrow passageway toward the uterus.

The ovaries (pronounced: OH-vuh-reez) are also part of the endocrine system because they produce female sex

such as estrogen (pronounced: ESS-truh-jun) and progesterone (pronounced: pro-JESS-tuh-rone).

How Does the Female Reproductive System Work?

The female reproductive system enables a woman to:

  • produce eggs (ova)
  • have sexual intercourse
  • protect and nourish a fertilized egg until it is fully developed
  • give birth

Sexual reproduction couldn’t happen without the sexual organs called the gonads. Most people think of the gonads as the male testicles. But both sexes have gonads: In females the gonads are the ovaries, which make female gametes (eggs). The male gonads make male gametes (sperm).

When a baby girl is born, her ovaries contain hundreds of thousands of eggs, which remain inactive until puberty begins. At puberty, the pituitary gland (in the central part of the brain) starts making hormones that stimulate the ovaries to make female sex hormones, including estrogen. The secretion of these hormones causes a girl to develop into a sexually mature woman.

Toward the end of puberty, girls begin to release eggs as part of a monthly period called the menstrual cycle. About once a month, during ovulation, an ovary sends a tiny egg into one of the fallopian tubes.

Unless the egg is fertilized by a sperm while in the fallopian tube, the egg leaves the body about 2 weeks later through the uterus — this is menstruation. Blood and tissues from the inner lining of the uterus combine to form the menstrual flow, which in most girls lasts from 3 to 5 days. A girl’s first period is called menarche (pronounced: MEH-nar-kee).

It’s common for women and girls to have some discomfort in the days leading to their periods. Premenstrual syndrome (PMS) includes both physical and emotional symptoms that many girls and women get right before their periods, such as:

  • acne
  • bloating
  • tiredness
  • backaches
  • sore breasts
  • headaches
  • constipation
  • diarrhea
  • food cravings
  • depression
  • irritability
  • trouble concentrating or handling stress

PMS is usually at its worst during the 7 days before a girl’s period starts and disappears after it begins.

Many girls also have belly cramps during the first few days of their periods caused by prostaglandins, chemicals in the body that make the smooth muscle in the uterus contract. These involuntary contractions can be dull or sharp and intense.

It can take up to 2 years from menarche for a girl’s body to develop a regular menstrual cycle. During that time, her body is adjusting to the hormones puberty brings. On average, the monthly cycle for an adult woman is 28 days, but the range is from 23 to 35 days.

What Happens If an Egg Is Fertilized?

If a female and male have sex within several days of the female’s ovulation, fertilization can happen. When the male ejaculates (when semen leaves the penis), a small amount of semen is deposited into the vagina. Millions of sperm are in this small amount of semen, and they “swim” up from the vagina through the cervix and uterus to meet the egg in the fallopian tube. It takes only one sperm to fertilize the egg.

About 5 to 6 days after the sperm fertilizes the egg, the fertilized egg (pronounced: zygote) has become a multicelled blastocyst. A blastocyst (pronounced: BLAS-tuh-sist) is about the size of a pinhead, and it’s a hollow ball of cells with fluid inside. The blastocyst burrows itself into the lining of the uterus, called the endometrium. The hormone estrogen causes the endometrium (pronounced: en-doh-MEE-tree-um) to become thick and rich with blood. Progesterone, another hormone released by the ovaries, keeps the endometrium thick with blood so that the blastocyst can attach to the uterus and absorb nutrients from it. This process is called implantation.

As cells from the blastocyst take in nourishment, another stage of development begins. In the embryonic stage, the inner cells form a flattened circular shape called the embryonic disk, which will develop into a baby. The outer cells become thin membranes that form around the baby. The cells multiply thousands of times and move to new positions to eventually become the embryo (pronounced: EM-bree-oh).

After about 8 weeks, the embryo is about the size of a raspberry, but almost all of its parts — the brain and nerves, the heart and blood, the stomach and intestines, and the muscles and skin — have formed.

During the fetal stage, which lasts from 9 weeks after fertilization to birth, development continues as cells multiply, move, and change. The fetus (pronounced: FEE-tis) floats in amniotic (pronounced: am-nee-AH-tik) fluid inside the amniotic sac. The fetus gets oxygen and nourishment from the mother’s blood via the placenta (pronounced: pluh-SEN-tuh). This disk-like structure sticks to the inner lining of the uterus and connects to the fetus via the umbilical (pronounced: um-BIL-ih-kul) cord. The amniotic fluid and membrane cushion the fetus against bumps and jolts to the mother’s body.

Pregnancy lasts an average of 280 days — about 9 months. When the baby is ready for birth, its head presses on the cervix, which begins to relax and widen to get ready for the baby to pass into and through the vagina. Mucus has formed a plug in the cervix, which now loosesn. It and amniotic fluid come out through the vagina when the mother’s water breaks.

When the contractions of labor begin, the walls of the uterus contract as they are stimulated by the pituitary hormone oxytocin (pronounced: ahk-see-TOE-sin). The contractions cause the cervix to widen and begin to open. After several hours of this widening, the cervix is dilated (opened) enough for the baby to come through. The baby is pushed out of the uterus, through the cervix, and along the birth canal. The baby’s head usually comes first. The umbilical cord comes out with the baby. It’s clamped and cut close to the navel after the baby is delivered.

The last stage of the birth process involves the delivery of the placenta, which at that point is called the afterbirth. After it has separated from the inner lining of the uterus, contractions of the uterus push it out, along with its membranes and fluids.

Reviewed by: Larissa Hirsch, MD Date reviewed: June 2019

In This Section

  • Sexual and Reproductive Anatomy
  • What are the parts of the female sexual anatomy?
  • What are the parts of the male sexual anatomy?

Sexual anatomy that’s typically called female includes the vulva and internal reproductive organs like the uterus and ovaries

What are the external parts?

The vulva is the part of your genitals on the outside of your body — your labia, clitoris, vaginal opening, and the opening to the urethra (the hole you pee out of). While vaginas are just one part of the vulva, many people say “vagina” when they really mean the vulva. But the vulva has a lot more going on than just the vagina.

No 2 vulvas look exactly the same, but they’re made up of the same basic parts.

  • Labia
    The labia (lips) are folds of skin around your vaginal opening. The labia majora (outer lips) are usually fleshy and covered with pubic hair. The labia minora (inner lips) are inside your outer lips. They begin at your clitoris and end under the opening to your vagina.
    Labia can be short or long, wrinkled or smooth. Often one lip is longer than the other. They also vary in color from pink to brownish black. The color of your labia can change as you get older. Some people have larger outer lips than inner lips, and many have larger inner lips than outer lips. Both are sensitive, and swell when you’re turned on.

  • Clitoris
    The tip of the clitoris (AKA glans) is located at the top of your vulva, where your inner lips meet. Everyone’s is a different size. It can be about as small a pea or as big as a thumb. The tip of the clitoris is covered by the clitoral hood.
    This is just the beginning of the clitoris though. It extends inside your body, back and down on both sides of the vagina. This part, called the shaft and crura (roots and legs), is about 5 inches long.
    Your clitoris is made of spongy tissue that becomes swollen when you’re aroused (turned on). It has thousands of nerve endings — more than any other part of the human body. And it’s only purpose? To make you feel good.

  • Opening of the urethra
    The urethral opening is the tiny hole that you pee out of, located just below your clitoris.

  • Opening of the vagina
    The vaginal opening is right below your urethral opening. It’s where menstrual blood leaves your body, and babies are born through the vaginal opening. A variety of things can go inside your vagina, like fingers, penises, sex toys, tampons, and menstrual cups.

  • Anus

    The anus (AKA butthole) is the opening to your rectum. The anus has lots of sensitive nerve endings, so some people experience sexual pleasure from anal stimulation.

  • Mons pubis
    The mons is the fleshy mound above your vulva. After puberty, it’s covered with pubic hair. It cushions your pubic bone.

What are the internal parts?

The internal parts of female sexual anatomy (or what’s typically referred to as female) include:

  • Vagina
    The vagina is a tube that connects your vulva with your cervix and uterus. It’s what babies and menstrual blood leave the body through. It’s also where some people put penises, fingers, sex toys, menstrual cups, and/or tampons. Your vagina is really stretchy, and expands when you feel turned on.

  • Cervix
    The cervix divides your vagina and uterus, located right between the two. It looks like a donut with a tiny hole in the middle. This hole connects your uterus and your vagina. It lets menstrual blood out and sperm in. Your cervix stretches open (dilates) during childbirth.
    You can usually feel your cervix at the end of your vagina if you insert your fingers, a penis, or a sex toy into your vagina. Your cervix separates your vagina from the rest of your body, so things like tampons or other objects can’t get “lost” inside of you.

  • Uterus
    The uterus is a pear-shaped muscular organ about the size of a small fist. It’s sometimes called the womb because it’s where a fetus grows during pregnancy. During sexual arousal, the lower part of your uterus lifts toward your belly button. That’s why your vagina gets longer when you’re turned on. It’s called “tenting.”

  • Fallopian tubes
    The fallopian tubes are 2 narrow tubes. They carry eggs from your ovaries to your uterus. Sperm travels through them to try to fertilize your egg.

  • Fimbriae
    The fimbriae look like tiny fingers at the end of each fallopian tube. When your ovary releases an egg, they sweep it into your fallopian tube.

  • Ovaries
    The ovaries store your eggs. They also produce hormones, including estrogen, progesterone, and testosterone. These hormones control things like your period and pregnancy. During puberty, your ovaries start to release an egg each month. They do so until menopause. Sometimes your ovaries release more than one egg.

  • Bartholin’s glands
    The Bartholin’s glands are near your vaginal opening. They release fluid that lubricates your vagina (makes it wet) when you’re turned on.

  • Skene’s glands
    The Skene’s glands are on either side of your urethral opening. They release fluid during female ejaculation.They’re also called paraurethral glands or female prostate glands.

  • Hymen
    The hymen is the thin, fleshy tissue that stretches across part of the opening to the vagina. Hymens vary a lot in how much of your vaginal opening they cover, and they can sometimes (but not always) tear and cause bleeding the first few times you put something in your vagina.

  • G spot
    The G spot, or Gräfenberg spot, is located on the front or belly-button side of your vagina. It’s a few inches inside your vagina. Your G-spot swells when you’re turned on. Some people like the feeling of having their G-spot touched.

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Center for Reproductive Health

To become pregnant, these steps must occur:

  1. Sperm Transport: The sperm must be deposited and transported to the site of fertilization
  2. Egg Transport: Ovulation must occur and the egg must be “picked up” by the tube
  3. Fertilization and Embryo Development: Union between the sperm and egg must result
  4. Implantation: The embryo must implant and begin to grow in the uterus

These steps are described in detail below.

Sperm Transport

The transport of sperm is dependent upon several factors. The sperm must be capable of propelling themselves through the environment of the female vagina and cervix. This environment, which is under cyclic hormonal control, must be favorable to admit the sperm without destroying them. Finally, the sperm must possess the capability of converting to a form that can penetrate the cell membrane of the egg (capacitation).

Following ejaculation, the semen forms a gel which provides protection for the sperm from the acidic environment of the vagina. The gel is liquefied within 20-30 minutes by enzymes from the prostate gland. This liquefaction is important to free the sperm so transportation may occur. The seminal plasma is left in the vagina. The protected sperm with the greatest motility travel through the layers of cervical mucus that guard the entrance to the uterus. During ovulation, this barrier becomes thinner and changes its acidity creating a friendlier environment for the sperm. The cervical mucus acts as a reservoir for extended sperm survival. Once the sperm have entered the uterus, contractions propel the sperm upward into the fallopian tubes. The first sperm enter the tubes minutes after ejaculation. The first sperm, however, are likely not the fertilizing sperm. Motile sperm can survive in the female reproductive tract for up to 5 days.

Egg Transport

Egg transport begins at ovulation and ends once the egg reaches the uterus. Following ovulation, the fimbriated (finger-like) end of the fallopian tube sweeps over the ovary. Adhesive sites on the cilia, which are located on the surface of the fimbriae, are responsible for egg pickup and movement into the tube. The cilia within the tube and muscular contractions resulting from the movement of the egg create a forward motion. Transport through the tube requires about thirty hours. Conditions such as pelvic infections and endometriosis can permanently impair the function of the fallopian tubes, due to scarring and or damage to the fimbriae.

Once the egg arrives at a specific portion of the tube called the ampullar-isthmic junction, it rests for another thirty hours. Fertilization (sperm union with the egg) occurs in this portion of the tube. The fertilized egg then begins a rapid descent to the uterus. The period of rest in the tube appears to be necessary for full development of the fertilized egg and preparation of the uterus for receipt of the egg. Defects in the fallopian tube may impair transport and increase the risk of tubal (ectopic) pregnancy.

Fertilization and Embryo Development

Following ovulation, the egg is capable of fertilization for only 12-24 hours. Contact between the egg and sperm is random. A membrane (shell) surrounding the egg, the zona pellucida, has two major functions in fertilization. First, the zona pellucida contains sperm receptors which are specific for human sperm. Second, once the membrane has been penetrated by the sperm, it becomes impermeable to penetration by other sperm.

Following penetration, a series of events set the stage for the first cell division. The single-cell embryo is called a “zygote.” Over the course of the next seven days, the human embryo undergoes multiple cell divisions in a process called mitosis. At the end of this transition period, the embryo becomes a mass of very organized cells called a blastocyst. As women get older, it is now believed, this process of early embryo development is increasingly impaired due to diminishing egg quality.

Implantation

Once the embryo reaches the blastocyst stage (approximately five to six days after fertilization), it hatches out of its zona pellucida (shell) and begins the process of implantation. In nature, 50% of all fertilized eggs are lost before a woman’s missed menses. So, too, in the in vitro fertilization (IVF) process an embryo may begin to develop but not make it to the blastocyst stage (the first stage where those cells destined to become the fetus separate from those which will become the placenta). The blastocyst may implant but not grow or the blastocyst may grow and still cease development before the two week time at which a pregnancy can be detected. The receptivity of the uterus and the health of the embryo are important for the implantation process.

The uterus

Uterine structure

The uterus, or womb, is shaped like an inverted pear. It is a hollow, muscular organ with thick walls, and it has a glandular lining called the endometrium. In an adult the uterus is 7.5 cm (3 inches) long, 5 cm (2 inches) in width, and 2.5 cm (1 inch) thick, but it enlarges to four to five times this size in pregnancy. The narrower, lower end is called the cervix; this projects into the vagina. The cervix is made of fibrous connective tissue and is of a firmer consistency than the body of the uterus. The two fallopian tubes enter the uterus at opposite sides, near its top. The part of the uterus above the entrances of the tubes is called the fundus; the part below is termed the body. The body narrows toward the cervix, and a slight external constriction marks the juncture between the body and the cervix.

The uterus does not lie in line with the vagina but is usually turned forward (anteverted) to form approximately a right angle with it. The position of the uterus is affected by the amount of distension in the urinary bladder and in the rectum. Enlargement of the uterus in pregnancy causes it to rise up into the abdominal cavity, so that there is closer alignment with the vagina. The nonpregnant uterus also curves gently forward; it is said to be anteflexed. The uterus is supported and held in position by the other pelvic organs, by the muscular floor or diaphragm of the pelvis, by certain fibrous ligaments, and by folds of peritoneum. Among the supporting ligaments are two double-layered broad ligaments, each of which contains a fallopian tube along its upper free border and a round ligament, corresponding to the gubernaculum testis of the male, between its layers. Two ligaments—the cardinal (Mackenrodt) ligaments—at each side of the cervix are also important in maintaining the position of the uterus.

The cavity of the uterus is remarkably small in comparison with the size of the organ. Except during pregnancy, the cavity is flattened, with front and rear walls touching, and is triangular. The triangle is inverted, with its base at the top, between the openings of the two fallopian tubes, and with its apex at the isthmus of the uterus, the opening into the cervix. The canal of the cervix is flattened from front to back and is somewhat larger in its middle part. It is traversed by two longitudinal ridges and has oblique folds stretching from each ridge in an arrangement like the branches of a tree. The cervical canal is 2.5 cm (about 1 inch) in length; its opening into the vagina is called the external os of the uterus. The external os is small, almost circular, and often depressed. After childbirth, the external os becomes bounded by lips in front and in back and is thus more slitlike. The cervical canal is lined by a mucous membrane containing numerous glands that secrete a clear, alkaline mucus. The upper part of this lining undergoes cyclical changes resembling, but not as marked as, those occurring in the body of the uterus. Numerous small cysts (nabothian cysts) are found in the cervical mucous membrane. It is from this region that cervical smears are taken in order to detect early changes indicative of cancer.

The uterus is composed of three layers of tissue. On the outside is a serous coat of peritoneum (a membrane exuding a fluid like blood minus its cells and the clotting factor fibrinogen), which partially covers the organ. In front it covers only the body of the cervix; behind it covers the body and the part of the cervix that is above the vagina and is prolonged onto the posterior vaginal wall; from there it is folded back to the rectum. At the side the peritoneal layers stretch from the margin of the uterus to each side wall of the pelvis, forming the two broad ligaments of the uterus.

The middle layer of tissue (myometrium) is muscular and comprises the greater part of the bulk of the organ. It is very firm and consists of densely packed, unstriped, smooth muscle fibres. Blood vessels, lymph vessels, and nerves are also present. The muscle is more or less arranged in three layers of fibres running in different directions. The outermost fibres are arranged longitudinally. Those of the middle layer run in all directions without any orderly arrangement; this layer is the thickest. The innermost fibres are longitudinal and circular in their arrangement.

The innermost layer of tissue in the uterus is the mucous membrane, or endometrium. It lines the uterine cavity as far as the isthmus of the uterus, where it becomes continuous with the lining of the cervical canal. The endometrium contains numerous uterine glands that open into the uterine cavity and are embedded in the cellular framework or stroma of the endometrium. Numerous blood vessels and lymphatic spaces are also present. The appearances of the endometrium vary considerably at the different stages in reproductive life. It begins to reach full development at puberty and thereafter exhibits dramatic changes during each menstrual cycle. It undergoes further changes before, during, and after pregnancy, during the menopause, and in old age. These changes are for the most part hormonally induced and controlled by the activity of the ovaries.

Chapter 4 – Anatomy and physiology of genital organs – women

“Anatomy is destiny”: Sigmund Freud viewed human anatomy as a necessary, although not a sufficient, condition for understanding the complexity of human sexual function with a solid biologic basis. The aim of the chapter is to describe women’s genital anatomy and physiology, focusing on women’s sexual function with a clinically oriented vision. Key points include: embryology, stressing that the “female” is the anatomic “default” program, differentiated into “male” only in the presence of androgens at physiologic levels for the gestational age; sex determination and sex differentiation, describing the interplay between anatomic and endocrine factors; the “clitoral–urethral–vaginal” complex, the most recent anatomy reading of the corpora cavernosa pattern in women; the controversial G spot; the role of the pelvic floor muscles in modulating vaginal receptivity and intercourse feelings, with hyperactivity leading to introital dyspareunia and contributing to provoked vestibulodynia and recurrent postcoital cystitis, whilst lesions during delivery reduce vaginal sensations, genital arousability, and orgasm; innervation, vessels, bones, ligaments; and the physiology of women’s sexual response. Attention to physiologic aging focuses on “low-grade inflammation,” genital and systemic, with its impact on women sexual function, especially after the menopause, if the woman does not or cannot use hormone replacement therapy.

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