Female reproductive organs

The female reproductive organs can be divided into the upper genital tract (i.e., uterus, fallopian tubes, ovaries, and cervix) and the lower genital tract (i.e., the vagina and vulva). The upper genital organs and the vagina are located in the pelvis, while the vulva is a part of the perineum. These organs participate in several hormonal and mechanical pathways that are responsible for secondary sexual development and reproduction. The uterine cavity is the site of embryonic implantation and fetal development. The cervix is the lower portion of the uterus and provides a passageway for the expulsion of uterine contents or the entry of spermatozoa into the uterine cavity. The ovaries are paired organs responsible for gametogenesis and sex hormone synthesis in females. In the middle of each menstrual cycle, a mature ovum ruptures out of a Graafian follicle and travels along the fallopian tubes, where it may be fertilized by sperm. The vagina is a hollow muscular structure that receives ejaculate during copulation and serves as a conduit for the expulsion of uterine contents. The vulva is the anterior portion of the perineum and is composed of the labia majora, the labia minora, the clitoris, and the mons pubis. The labia envelop the clitoris, the urethral orifice, and the vaginal introitus.

Function ^[1]

• Uterus
  • Site of implantation of the fertilized ovum
  • Protects and supports the growth of the fetus
  • Site of menstruation; see physiology of the menstrual cycle.
• Cervix
  • Promotes entry of sperm into the uterus for fertilization
  • Allows menstrual blood to flow from the uterus into the vagina
  • The endocervix secretes a clear, alkaline fluid to facilitate the passage of sperm.

Gross anatomy ^[1]

Overview

• Location
  • The uterus and cervix are located within the pelvis.
  • The uterus is located posterior to the bladder and anterior to the rectum.
  • The cervix is the most distal aspect of the uterus and protrudes into the fundus of the vagina.
  • Most of the uterine body and posterior supravaginal cervix are covered by peritoneum.
• Position
  • The uterus is most commonly anteverted by 90° and anteflexed by 120°.
  • Other variants (e.g., retroflexion) occur in 10% of women and may impair conception.
• Neighboring structures
  • Anteriorly: uterovesical pouch
  • Posteriorly: rectouterine pouch
  • Laterally: fallopian tubes, folds of peritoneum (including broad ligament), round ligament, ovarian ligament, cardinal ligament

Structure

• Uterine fundus: superior, rounded aspect of the uterus
• Body
  • Uterine horns: site of the opening of the fallopian tubes bilaterally
  • Uterine cavity: triangular; continuous with the uterine tube and internal os
• Isthmus:
  • Constriction between the body and the cervix
  • Corresponds to the level of the internal os of the uterus
• Cervix: fibrous, cylindrical part of the distal uterus between the internal and external orifice
  • Supravaginal cervix: portion of the cervix superior to the vagina
  • Vaginal cervix: portion of the cervix that protrudes into the fundus of the vagina
  • Cervical canal
  • Cervical os: the opening of the cervix into the vagina

Vasculature

Ligation of the uterine arteries (e.g., during hysterectomy) carries a risk of ureter injury!

Lymphatics

Innervation ^[1][2]

Ligaments

• See “Ligaments of the female pelvis” below.

Uterus

The uterus is composed of three layers. From internal to external:

1. Endometrium: mucosal layer consisting of two layers
   1. Simple columnar epithelium with tubular glands
      • Functional layer of the endometrium: proliferates and then sloughs during the menstrual cycle
      • Tubular glands are long during the proliferative phase and coiled during the secretory phase.
   2. Connective tissue (stroma)
2. Myometrium: smooth muscle layer
   • Contains blood vessels, nerves, and lymphatics
   • Composed of smooth muscle and loose connective tissue
3. Perimetrium
   • Uterine body: covered by peritoneal serosa
   • Anterior cervix and lateral uterine body: adventitia (not covered by peritoneum)

Cervix

Composed primarily of fibroelastic connective tissue. Can be divided into:

1. Endocervix: inner part of the cervix proximal to the uterine external os
   • Composed of simple columnar epithelium with mucous-producing cells
2. Cervical transformation zone: physiologic transition zone between the endocervix and ectocervix
   • Exact location is variable
   • Site of the squamocolumnar junction: the border between metaplastic squamous epithelium and simple columnar epithelium
   • Cervical cancer most commonly occurs in this zone.
3. Ectocervix: outer part of the cervix distal to the uterine external os
   • Composed of stratified squamous epithelium (nonkeratinized)

Embryology ^[1][3]

• Derivatives
  • Paramesonephric duct (Müllerian duct) → uterus, cervix, fallopian tubes, and proximal part of the vagina
  • See development of the reproductive system and anomalies of the female genital tract.
• Timing
  • Fusion of the two paramesonephric ducts begins in the 7^th–8^th week of gestation and is complete by the 12^th week.
  • The cervix differentiates from the body of the uterus by the 10^th week of gestation.
  • The uterine septum disappears by the 22^nd week of gestation.
• Paramesonephric duct anomalies
  • Septate uterus
  • Bicornuate uterus
  • Didelphic uterus

Function ^[1]

• During ovulation, an oocyte from the ovary enters the distal segment of a fallopian tube.
• Most common site of fertilization by sperm: the ampulla
• Movement of cilia and contraction of the muscular layer facilitate the transport of ovum to the uterus for implantation.
• Secretion of nutrients for gametes

Gross anatomy ^[1]

Overview

• Location
  • Extend bilaterally from the horns of the uterus
  • Contained in the proximal part of the broad ligament
• Neighboring structures: open near the ovaries into the abdominal cavity

Structure

• Fimbria
  • Ciliated end of the fallopian tube
  • Receives the ovum from the ovary
• Infundibulum: funnel-shaped opening with attached fimbriae
• Ampulla: widest part; most common site of fertilization
• Isthmus: narrowest part
• Intramural: located in the myometrium of the uterus; connects the ampulla to the uterus

Vasculature

Lymphatics

• Paraaortic nodes
• Internal iliac nodes
• Round ligament → inguinal nodes

Innervation

Ligaments

• Broad ligament
• See “Ligaments of the female pelvis” below.

Microscopic anatomy ^[1]

The fallopian tubes are made up of three layers. From internal to external:

• Mucosa: : lined with simple ciliated columnar epithelium and secretory Peg cells
• Muscular layer: smooth muscle layer that facilitates the transportation of the ovum
  • Inner circular smooth muscle layer
  • Outer longitudinal smooth muscle layer
  • Contraction is sensitive to estrogen.
• Serosa: highly vascular layer surrounding the fallopian tubes

Embryology ^[3]

• Derived from the paramesonephric duct
• See “Development of the reproductive system.”

Function

• Site of oogenesis
• Sex hormone synthesis: estrogen, progesterone, testosterone

Gross anatomy ^[1]

Overview

• Description: paired, ovoid-shaped reproductive organs
• Location
  • Lateral to the uterus and close to the lateral pelvic wall
  • Suspended in the mesovarium (attached to the posterior part of the broad ligament)
• Neighboring structures: close proximity to the cecum and appendix on the right side and the sigmoid colon on the left side

Vasculature

The Left Gonadal vein is the LonGest.

Lymphatics

• Primarily: paraaortic nodes
• Rarely: inguinal nodes (via round ligament)

Innervation

• Ovarian plexus and uterine plexus via the suspensory ligament
  • Sympathetic (T10–11) → vasoconstriction
  • Parasympathetic (S2–S4)
  • Visceral afferent fibers

Ligaments

• Mesovarium
• Ovarian ligament
• Infundibulopelvic ligament
• See ligaments of the female pelvis below.

Microscopic anatomy ^[1]

Layers of the ovary

• Outer layer: : peritoneum (simple cuboidal epithelium, germinal epithelium)
• Capsule (tunica albuginea): thick layer of collagen
• Cortex: dense connective tissue surrounding the ovarian follicles and corpora lutea
• Medulla: loose connective tissue containing vessels and nerves

Ovarian follicle

The ovarian follicle is a functional unit of the ovaries that matures during the menstrual cycle (see “Folliculogenesis” below).

• Oocyte: Each follicle contains a single oocyte.
• Granulosa cells (follicular cells): form the stratum granulosum
  • Surround the oocyte and form the follicular cavity
  • Stimulated by FSH
  • Inhibited by LH
• Theca cells
  • Surround the granulosa cells and form a basement membrane
  • Theca interna: androstenedione synthesis
  • Theca externa: layer of connective tissue

Embryology

• Mesoderm → undifferentiated gonads → ovaries
• See “Development of the reproductive system.”

Oogenesis ^[1]

• Oogenesis is the development of an immature oocyte into a secondary oocyte or mature ovum (if fertilization occurs).
• Begins in utero during fetal growth and ends with menopause
• At birth, a normal ovary contains about 1–2 million primary oocytes.
• There is a continuous decline in the number of primary oocytes after birth.

Folliculogenesis ^[1]

• Definition: the maturation of ovarian follicles (required for oogenesis)
• Sequence: primordial follicle → primary follicle → secondary follicle → tertiary follicle → corpus luteum
• See “Oogenesis” above and “Menstrual cycle and menstrual cycle abnormalities.”

Primary oocyte arrest occurs in prophase I of meiosis I (think PROphase = PRior to Ovulation).
Secondary oocyte arrest occurs in metaphase II of meiosis II (think METaphase = before egg MET sperm).Primary oocytes are formed prior to birth to serve as an ovarian reserve.

Function ^[1]

• Vagina
  • Passageway for menstrual blood
  • Conduit for childbirth
  • Barrier against ascending infections: due to its acidic pH 4–4.5
• Vulva
  • Secretion of alkaline fluid for lubrication during sex (greater vestibular glands)
  • Sexual arousal and female sexual response
  • See “Sexuality and sexual medicine.”

Gross anatomy ^[1]

The vagina and vulva collectively make up the lower genital tract.

Vagina

Position

• Location
  • Extraperitoneal, in the pelvis
  • Extends from the uterus to the vaginal vestibule
• Neighboring structures
  • Supported by the levator ani muscle, urogenital diaphragm, and several ligaments: transverse cervical ligament, pubocervical ligament, and sacrocervical ligament
  • Anteriorly: urethra and bladder
  • Posteriorly: rectum and anal canal (separated by perineal body)
  • Superiorly: rectouterine pouch
  • Distally: pelvic floor and vulva
  • The ureter courses close to the lateral fornices.

Structures

• Vaginal fornix: recess between the vagina and the cervix
  • Four fornices: anterior, posterior, and two lateral
  • The posterior vaginal fornix is the deepest and lies below the rectouterine pouch.
• Hymen: membrane that partially covers or surrounds the vaginal opening

Hymen atresia causes complete occlusion of the vagina, which obstructs blood flow at menarche, causing primary amenorrhea.

Vulva

Position

• Location: external to the pelvis
• Neighboring structures: continuous with the perineum

Structures

• Labia majora: folds of skin that surround and cover the vaginal ostium and the labia minora
• Labia minora: folds of hairless skin that surround the vaginal vestibule
• Vulval vestibule: cavity between the labia minora that contains the vaginal and urethral orifices
  • Greater vestibular glands (Bartholin gland)
    • Homologous to the male bulbourethral glands
    • Secrete alkaline fluid for lubrication
  • Skene glands:
    • Homologous to the male prostate gland
    • Exact function is unknown
  • Bulbs of the vestibule: erectile tissue that flanks the vaginal orifice
• Clitoris: anterior to the labia minora; erectile tissue composed of corpora cavernosa

Estrogen stimulates proliferation and keratinization of the vulvar epithelium. Menopause with decreased estrogen levels results in vulvar atrophy.

Pudendal nerve block is often used for anesthesia prior to vaginal procedures, childbirth, or episiotomy.

Microscopic anatomy ^[1]

Vagina

The vagina is a fibromuscular structure with numerous transverse vaginal rugae.

• Inner mucosal layer
  • Nonkeratinized stratified squamous epithelium
  • Epithelial cells are rich in glycogen.
    • Vaginal bacteria break down glycogen → lactic acid, forming a highly acidic environment
    • Glycogen content increases after ovulation
• External muscular layer
  • Outer longitudinal smooth muscle layer
  • Inner circular smooth muscle layer
• Hymen: nonkeratinized stratified squamous epithelium

Vulva

• Labia minora
  • Nonkeratinized stratified squamous epithelium
  • Rich in sebaceous glands
• Labia majora
  • Keratinized stratified squamous epithelium
  • Hair follicles
  • Eccrine, apocrine, and sebaceous glands
• Vestibule: nonkeratinized squamous epithelium with major vestibular and minor vestibular glands
• Urethra: columnar epithelium with minor vestibular glands

Embryology ^[1]

• Paramesonephric ducts (Müllerian ducts) → upper third of the vagina
• Urogenital sinus → lower two-thirds of the vagina, vaginal vestibule, vestibular glands
• Urogenital folds → labia minora
• Labioscrotal swelling → labia majora
• Genital tubercle → clitoris
• See “Development of the reproductive system.”

References:^[4]

During ligation of the ovarian artery and vein, care must be taken not to damage the ureter, which is located directly posterior to the infundibulopelvic ligament, close to the medial leaf of the broad ligament.

The Cardinal ligament connects the Cervix with the pelvic wall.

References: ^[1]

General conditions

• Differences (disorders) of sex development
• Anomalies of the female genital tract
• Menstrual cycle and menstrual cycle abnormalities
• Sexually transmitted infections
• Urethritis

Uterine conditions

• Adenomyosis
• Uterine leiomyoma
• Endometriosis
• Endometrial hyperplasia
• Endometrial carcinoma
• Endometritis
• Endometrial polyp
• Abnormal uterine bleeding
• Septate uterus
• Bicornuate uterus
• Uterus didelphys
• Asherman syndrome

Cervical conditions

• Cervical dysplasia
• Cervical cancer

Ovarian conditions

• Polycystic ovarian syndrome
• Primary ovarian insufficiency
• Ovarian cysts
• Ovarian cancer
• Germ cell tumors
• Sex cord-stromal tumors of the ovary

Vaginal and vulvar conditions

• Imperforate hymen
• Vulvovaginitis
• Bartholin gland cyst
• Vulvar and vaginal cancer