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Vulva, vagina & female urethra

General

Anatomy & histology-vulva, vagina & female urethra

Authors: Jesus Adrian Chavez, M.D., Debra L. Zynger, M.D., Monika Roychowdhury, M.D.

Last author update: 1 February 2013

Last staff update: 22 August 2023 (update in progress)

Copyright: 2002-2023, PathologyOutlines.com, Inc.

PubMed Search: Anatomy vulva vagina

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Table of Contents

Cite this page: Chavez JA, Zynger DL, Roychowdhury M. Anatomy & histology-vulva, vagina & female urethra. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/vulvaanatomy.html. Accessed September 26th, 2023.

Embryology

4 weeks:
- Germ cells arise from yolk sac
5 - 6 weeks:
- Germ cell migrate to urogenital ridge, mesothelium of urogenital ridge proliferates to form epithelium and stroma of gonad, incorporating germ cells, resulting in elevation of overlying ectoderm
- Anteriorly, this results in the formation of the genital tubercle, which becomes the clitoris
- Laterally, two parallel ridges, each composed of a medial and lateral fold, develop into the labia minora
- They are joined anteriorly to form the clitoral frenulum and posteriorly to form the fourchette or posterior frenulum of the labia
- Epithelium of the labia minora and of the clitoral hood are of ectodermal origin
By the end of 6 weeks:
- Urorectal septum divides the cloaca anteriorly in the urogenital sinus, posteriorly in the anal canal; both of these structures are covered respectively by the urogenital and the anal membrane
- Degeneration of the central portion of the urogenital membrane results in the hymen opening
- Lateral Müllerian ducts (paramesonephric ducts) form from fusion of coelomic lining epithelium, proximal portion forms fallopian tubes, caudal portion fuses to form uterus, upper vagina
- Urogenital sinus forms lower vagina and vestibule, fuses with Müllerian ducts
By 16th week:
- Junction of the distal vagina with the urogenital sinus results in the development of the vaginal vestibule, which is identifiable by the 16th week
- Vaginal vestibule is of endodermal origin except for a small area immediately anterior to the urethra, which is of ectodermal origin - this area represents the site of insertion of the urethral septum, dividing the urethra from the genital tubercle
- Junction of the epithelium derived from endoderm and that derived from ectoderm is seen in the adult on the inner aspects of the labia minora, marked by the junction of keratinized with nonkeratinized epithelium
- This line of demarkation is referred to as the vestibular line of Hart
In men:
- Müllerian inhibitory substance from testes causes regression of Müllerian ducts and paired Wolffian (mesonephric) ducts form epididymis and vas deferens
- If no functional testes, Müllerian ducts persist and mesonephric duct regresses; mesonephric duct vestiges may persist as Gartner duct cysts in cervix or vagina

Vulva

Vulva:
- Immediately external to vagina
- Composed of: mons pubis, clitoris, labia minora, labia majora, vulvar vestibule, vestibulovaginal bulbs, urethral meatus, hymen, Bartholin and Skene glands and ducts, vaginal introitus
Bartholin glands:
- Corresponds to bulbourethral glands in male
Clitoris:
- Erectile tissue similar to corpora cavernosa of penis
- Lymphatics drain to deep inguinal nodes
Hymen:
- Nonkeratinized stratified squamous epithelium
Labia majora:
- Form the lateral boundaries of the vulva
- Composed of folds of adipose and fibrous tissue
- Fuse anteriorly into mons pubis
- Posteriorly terminate 3 - 4 cm anterior to anus where they are united by posterior commissure or fourchette
- Histologically, skin contains outer lining of stratified squamous epithelium, consisting of basal layer of cells (stratum malpighii), thin granular layer and horny layer
- Composed of keratinized stratified squamous epithelium with hair follicles and eccrine, apocrine and sebaceous glands
Labia minora:
- Consist of two folds of connective tissue which contain little or no adipose tissue
- Anteriorly, labia minora divide into two parts
- One part passes over clitoris to form prepuce
- Other joins beneath clitoris and forms frenulum
- Posteriorly, they blend with medial surfaces of labia majora
- Skin and mucosa of labia minora are rich in sebaceous glands
- Deeper area contains dense connective tissue
- Composed of nonkeratinized stratified squamous epithelium, usually no adnexae
Vestibule:
- Area between the hymen and Hart line
- Lined by nonkeratinized squamous epithelium
- Structures found in vestibule include: major vestibular (Bartholin) glands, minor vestibular glands, periurethral (Skene) glands, urethra
Minor vestibular gland:
- Correspond to penile glands of Littre
- Concentrically located within the vestibule
- Shallow glands (extending no deeper than 3 mm into the underlying dermis) lined by single layer of mucin secreting columnar cells that merge with stratified squamous epithelium of vestibule
- Open directly onto the surface
Glands:
- Apocrine glands (scent glands):
  - Develop secretory function at adrenarche
  - Identical to those of axillae, breast and perianal regions
  - Height of secretory cells varies
  - Lumina of glands are large compared to lumina of eccrine glands
- Eccrine glands (sweat glands):
  - Primarily involved in heat regulation
  - Function before puberty
  - Lined by layer of epithelial cells that contain eosinophilic cytoplasm
- Sebaceous glands:
  - Alveolar, holocrine glands which do not contain lumina
  - Each gland composed of several lobules
  - Cells in each lobule form delicate network filled with fat
- Skene glands:
  - Periurethral glands analogous to prostate
  - Mucus secreting columnar epithelium merges with duct urothelium, then stratified squamous epithelium of vestibule
Vulvar lymphatics:
- Drainage for all but clitoris is to superficial inguinal nodes

Vagina

Extends from vulva to uterine cervix
Derived from paired Müllerian ducts
Layers are mucosa, muscularis, adventitia
Mucosa composed of basal, intermediate and superficial squamous epithelium; responsive to steroid hormones
Lamina propria (subepithelial stroma) composed of elastic fibers, rich venous and lymphatic network, some multinucleated stellate stromal cells
Wolffian (mesonephric) duct, aka Gartner duct, runs deeply along lateral vaginal walls; single small duct surrounded by cluster of small glands lined by cuboidal epithelium with eosinophilic secretion in lumen
Lymphatic drainage: external iliac nodes (upper anterior wall), deep pelvic, rectal and aortic nodes (posterior vagina), interiliac nodes (lower vagina), also inferior gluteal and femoral nodes
Maturation index:
- Ratio of parabasal to intermediate to superficial cells of vaginal epithelium (sampled at middle third of lateral vaginal wall)
- Sample often obtained simultaneous with Pap smear to detect hormonal effects in menopausal and postmenopausal women
- Increased maturation in vaginal epithelium may be due to estrogenic effect of tamoxifen (Clin Exp Obstet Gynecol 1998;25:121)

Female urethra

Definition / general

Fibromuscular tube lined by urothelium, columnar epithelium and nonkeratinizing squamous epithelium that takes urine from the urinary bladder to the exterior through the external urethral meatus (Ross: Histology - A Text and Atlas, 7th Edition, 2015, Bostwick: Urologic Surgical Pathology, 3rd Edition, 2014)
Subepithelium composed of loose fibroelastic tissue, glands and abundant vessels
Muscle layers include smooth muscle and exterior skeletal muscle
Size, structure and function differ in males and females

Clinical features

Extends from the bladder to the vestibule of the vagina to its opening posterior to the clitoris (Ross: Histology - A Text and Atlas, 7th Edition, 2015, Bostwick: Urologic Surgical Pathology, 3rd Edition, 2014)
Measures 4 cm in length
Epithelium is derived from endoderm of the urogenital sinus and the surrounding connective tissue and smooth muscle tissue is derived from splanchnic mesenchyme (Bostwick: Urologic Surgical Pathology, 3rd Edition, 2014)
Lined by urothelium (proximal two - thirds), stratified and pseudostratified columnar and squamous epithelium (distal third)
Periurethral (Skene) glands (homologous to the prostate gland) open into the distal portion
Minor vestibular glands (homologous to glands of Littré in males) open along the entire length
Striated muscle of the urogenital diaphragm forms the external voluntary sphincter as the urethra penetrates it (Ross: Histology - A Text and Atlas, 7th Edition, 2015)

Microscopic (histologic) description

Urothelium
- Basal layers composed of either low columnar or cuboidal cells, followed by several layers of polyhedral cells
- Most superficial layer composed of round, dome shaped umbrella cells that are occasionally multinucleated and flattened according to amount of distention
Nonkeratinizing squamous epithelium
- Composed of multiple layers
- Divided in zones according to cell shapes: cuboidal (deepest), polymorphous (middle), squamous / flattened (superficial)
Periurethral glands
- Periurethral (Skene) glands: lined by columnar or cuboidal epithelium with surrounding connective tissue and smooth muscle (Ann Anat 2002;184:341)
- Minor vestibular glands (Littré glands): tubuloacinar - mucinous glands with uniform, pale eosinophilic to clear cytoplasm and basally flattened nuclei in penile urethra (Mills: Histology for Pathologists, 4th Edition, 2012)