Vaginal canal

The vaginal canal is a fibromuscular tube forming the lower part of the female genital tract. It extends from the cervix of the uterus to the external vaginal orifice and serves multiple roles in reproduction, menstruation, and childbirth. The canal is capable of significant distension and is lined by a stratified squamous epithelium that is adapted to friction and hormonal changes. It serves as the receptacle for the penis during intercourse, the outflow tract for menstrual blood, and the birth canal during delivery.

Structure

The vaginal canal is a collapsed, distensible fibromuscular tube with anterior and posterior walls normally in contact. It has rugae (transverse folds) that allow expansion during sexual intercourse and childbirth. The wall is composed of three layers: mucosa, muscularis, and adventitia.

• Length: Approximately 7–9 cm (posterior wall longer than anterior)
• Shape: Flattened anteroposteriorly; forms a H-shaped lumen in cross-section
• Orientation: Directed upward and backward; forms an angle (~60°) with the horizontal plane

Wall Layers

1. Mucosa: Non-keratinized stratified squamous epithelium; no glands
2. Muscularis: Smooth muscle — inner circular and outer longitudinal layers
3. Adventitia: Dense connective tissue with rich vascular and nerve supply

Fornices

The upper end of the vaginal canal surrounds the cervix, forming the vaginal fornices:

• Anterior fornix
• Posterior fornix: Deepest; adjacent to rectouterine pouch (of Douglas)
• Lateral fornices

Location

The vaginal canal extends from the external vaginal opening in the vulva to the cervix, lying between the bladder/urethra anteriorly and the rectum/posterior wall of the perineum posteriorly. It passes through the urogenital hiatus of the pelvic diaphragm and opens externally between the labia minora.

Function

• Copulatory Canal: Receives the penis and semen during intercourse
• Menstrual Passage: Acts as an outflow tract for menstrual blood and tissue
• Birth Canal: Dilates and stretches significantly during childbirth
• Protective Barrier: Epithelium and acidic environment protect against pathogens

Blood Supply

• Arterial:
  • Vaginal artery (branch of internal iliac)
  • Branches from uterine, internal pudendal, and middle rectal arteries
• Venous: Vaginal venous plexus → internal iliac vein

Lymphatic Drainage

• Upper third: Internal and external iliac nodes
• Middle third: Internal iliac nodes
• Lower third: Superficial inguinal lymph nodes

Innervation

• Upper 3/4: Visceral innervation via uterovaginal plexus (from inferior hypogastric plexus)
• Lower 1/4: Somatic innervation via deep perineal branch of pudendal nerve (S2–S4)
• Sensation: Only the lower portion is sensitive to pain, temperature, and touch

Embryological Development

• Upper portion: Derived from the paramesonephric (Müllerian) ducts
• Lower portion: Derived from the urogenital sinus

Clinical Significance

• Vaginitis: Inflammation due to infections (bacterial, fungal, parasitic)
• Atrophic Vaginitis: Postmenopausal thinning and dryness of vaginal mucosa
• Fistulas: Abnormal connections (e.g., vesicovaginal, rectovaginal) may develop after trauma or surgery
• Prolapse: Vaginal wall prolapse (cystocele, rectocele) may result from pelvic floor weakness
• Foreign Bodies: Tampons or contraceptive devices left in situ may cause infection or discharge