13.13: Uterus and Uterine Tubes — Structures That Support Fertilization and Pregnancy
- Page ID
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)The female reproductive tract supports fertilization, pregnancy, and childbirth through coordinated anatomy and hormone-regulated processes.
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Identify the main structures of the female reproductive tract, explain their anatomy and state their basic functions.
Figure \(\PageIndex{1}\): Female reproductive tract. The female reproductive tract includes the uterine tubes, uterus, cervix, and vagina. The uterine tubes extend from the uterus and end in finger-like fimbriae that help guide the oocyte into the tube after ovulation. The uterus is a muscular organ that supports implantation, pregnancy, and childbirth. Inferior to the uterus, the cervix forms a narrow passage that opens into the vagina at the external os. The vagina is a muscular canal that allows menstrual flow to exit the body, receives sperm during intercourse, and serves as the birth canal during delivery.
Uterine Tubes
The uterine tubes, also called Fallopian tubes or oviducts, serve as the passageway that transports the oocyte from the ovary to the uterus (see figure13.13.1, above). Each uterine tube lies close to an ovary but is not directly attached to it. The widened, distal end of the tube flares outward and forms finger-like projections called fimbriae, which sweep over the surface of the ovary and help guide the oocyte into the tube after ovulation. Because the oocyte cannot move on its own, it relies on the uterine tube to transport it. Around ovulation, high estrogen levels cause the smooth muscle of the tube to contract and the cilia to beat more strongly. Together, these actions help sweep the oocyte into the uterine tube and slowly move it toward the uterus.
Watch this video(opens in new window) to observe ovulation and its initiation in response to the release of FSH and LH from the pituitary gland. What specialized structures help guide the oocyte from the ovary into the uterine tube?
If fertilization occurs, it usually happens in the ampulla, the middle region of the uterine tube. The inner lining of the tube contains mucus-secreting cells and ciliated columnar cells. The coordinated beating of the cilia toward the uterus creates a gentle current that moves the oocyte, or a fertilized ovum, from the distal end of the tube toward the uterine cavity.
In case fertilization occurs, the resulting zygote begins dividing as it travels through the uterine tube toward the uterus. It progresses from two cells to four cells and beyond during this journey. Once it reaches the uterus, the developing embryo implants in the uterine wall and continues to grow. If fertilization does not occur, the oocyte breaks down either in the uterine tube or in the uterus and is eventually reabsorbed or shed from the body during the next menstrual period.
When an Infection Travels Upstream
Because the uterine tubes are open near the ovaries, they create a potential pathway for infection to spread upward through the female reproductive tract and end up in the pelvic cavity. Pelvic inflammatory disease (PID) most often develops when bacteria from a sexually transmitted infection (STI) ascend from the vagina and cervix into the uterus, uterine tubes, and beyond. If not treated promptly, the infection can spread further and, in rare cases, enter the bloodstream, leading to sepsis, a life-threatening condition.
Untreated PID can not only cause inflammation, but also lead to scarring, and adhesions within the reproductive tract. These structural changes increase the risk of infertility, ectopic pregnancy, and chronic pelvic pain. Early diagnosis and treatment are critical to prevent long-term complications.
Symptoms and Diagnosis
PID does not always cause noticeable symptoms. Many people with evidence of previous PID were unaware they ever had an infection. Even when symptoms are absent, permanent damage to the reproductive tract can still occur.
The risk of PID is also increased when procedures such as abortions are performed under non-sterile conditions, as bacteria that normally live in the vagina can move upward into the uterus and uterine tubes. Co-infections with multiple microorganisms are common.
When symptoms do occur, they may include:
- Lower abdominal or pelvic pain
- Fever
- Unusual vaginal discharge
- Irregular menstrual bleeding
- Pain during sexual intercourse
Diagnosis often involves a combination of clinical evaluation, laboratory testing for STIs, and imaging studies such as pelvic ultrasound.
Infectious Agents
PID can be caused by several different microorganisms, but the most common causes are the sexually transmitted bacteria Chlamydia trachomatis and Neisseria gonorrhoeae, the causative agents of chlamydia and gonorrhea. These two infections are among the most common STIs in the United States.
Treatment
PID is treated with antibiotics. Mild cases are usually managed with oral medications, while more severe infections may require intravenous antibiotics. Symptoms often begin to improve within a few days of starting treatment.
Sexual partners should also be treated to prevent reinfection. Even after the infection has resolved, scar tissue within the uterine tubes may remain and can block the passage of an oocyte, increasing the risk of infertility or ectopic pregnancy.
Uterus and Cervix
The uterus is a muscular organ that supports and nourishes a developing embryo. When a female is not pregnant, the uterus is about 5 cm wide and 7 cm long, roughly the size of a small pear.
T
he uterus has three main regions:
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Fundus: the rounded, upper portion of the uterus, located above the openings of the uterine tubes
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Body (corpus): the large central portion of the uterus
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Cervix: the narrow, lower portion of the uterus that extends into the vagina
The cervix produces mucus that changes throughout the menstrual cycle. When estrogen levels are high, this mucus becomes thin and slippery, which helps sperm move more easily through the cervix and into the uterus.
Layers of the Uterine Wall
The wall of the uterus consists of three layers (see figure on the right):
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Perimetrium: the thin, outer layer that covers and protects the uterus
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Myometrium: a thick layer of smooth muscle that makes up most of the uterine wall. It is responsible for uterine contractions. Strong contractions occur during labor to help deliver the baby, while weaker contractions occur during menstruation to help expel menstrual blood. Near the time of ovulation, gentle uterine contractions may also help move sperm through the reproductive tract.
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Endometrium: the innermost lining of the uterus. For more details see below:
The Endometrium
The innermost layer of the uterus is called the endometrium. It lines the uterine cavity and is the tissue that thickens each month in preparation for a possible pregnancy. The endometrium is made of connective tissue (called the lamina propria) covered by epithelial cells that face the uterine lumen.
Structurally, the endometrium has two layers:
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Stratum basalis (basal layer)
This thin layer lies next to the myometrium (the muscular wall of the uterus). It does not shed during menstruation. Instead, it remains in place and serves as the source of cells that rebuild the endometrium after each menstrual cycle. -
Stratum functionalis (functional layer)
This thicker, inner layer faces the uterine cavity. It contains uterine glands and blood vessels and is the portion of the endometrium that responds to hormones. This functional layer grows and thickens in response to estrogen and progesterone. If pregnancy does not occur, this is the layer that is shed during menstruation.
Female Reproductive System
Female fertility is highest in the twenties, declines gradually through the thirties, and decreases more rapidly after age 35. Fertility ends at menopause, which occurs when ovarian follicles are depleted and estrogen production falls. A woman is considered menopausal after 12 consecutive months without menstruation, with the average age occurring between 50 and 52 years.
As menopause approaches, declining inhibin levels lead to increased FSH secretion. Although more follicles are stimulated to grow, most undergo atresia, eventually resulting in a sharp drop in estrogen. This hormonal change is responsible for most menopausal symptoms.
During perimenopause, menstrual cycles become irregular and progesterone levels decline, which can increase the risk of endometrial hyperplasia. Common symptoms include hot flashes, night sweats, sleep disturbances, mood changes, and vaginal dryness, though severity varies widely.
After menopause, low estrogen levels increase the risk of cardiovascular disease and osteoporosis. Hormone therapy may relieve symptoms in some women but is typically used at the lowest effective dose for the shortest possible time due to potential risks.