Anatomy and Physiology of the vagina

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Overview

• The vagina is a fibromuscular canal extending from the vulva to the cervix, forming part of the lower female genital tract.
• Functions include sexual intercourse, menstrual outflow, and acting as the birth canal during vaginal delivery.

📍 Location and Relations

• Runs posterosuperiorly from the vestibule to the cervix (typically ~7–10 cm, variable).
• Anterior: bladder base and urethra.
• Posterior: rectum (upper posterior wall related to the pouch of Douglas/peritoneum).
• Lateral: levator ani and pelvic fascia; ureters lie close to the cervix (clinically relevant in surgery).

🧱 Gross Structure

• Upper end: surrounds the cervix to form the vaginal fornices (anterior, posterior, and two lateral).
• Lower end: opens into the vaginal vestibule (between the labia minora).
• Anterior vs posterior walls: the posterior wall is usually longer due to the cervix position.
• The mucosa forms transverse folds called rugae (more prominent in premenopausal states).

🔬 Histology

• Mucosa: stratified squamous non-keratinised epithelium (protective; no glands).
• Lamina propria: elastic fibres, venous plexuses, immune cells (local defence).
• Muscularis: smooth muscle (inner circular + outer longitudinal) with variable thickness.
• Adventitia: connective tissue anchoring to pelvic structures; contains vessels and nerves.
• No vaginal glands: lubrication mainly from cervical mucus and transudation through the vaginal wall; vestibular glands contribute to vulval lubrication.

🩸 Blood Supply

• Arterial supply: predominantly from the vaginal artery (branch of internal iliac) and contributions from the uterine artery and internal pudendal artery.
• Venous drainage: vaginal venous plexus → internal iliac veins (rich venous plexus can bleed significantly with trauma).

🧠 Nerve Supply

• Upper vagina (autonomic): visceral afferents via the uterovaginal plexus (inferior hypogastric plexus) → pain tends to be poorly localised.
• Lower vagina (somatic): via pudendal nerve → touch/pain is well localised (important for procedures and childbirth pain).

🧬 Lymphatic Drainage

• Upper vagina: internal iliac ± external iliac nodes.
• Middle vagina: internal iliac nodes.
• Lower vagina and introitus: superficial inguinal nodes.
• Clinically important for vaginal and cervical malignancy staging and patterns of spread.

🏗️ Support and Pelvic Floor Relations

• Supported by the levator ani (especially pubococcygeus/puborectalis), perineal body, and endopelvic fascia.
• The perineal body is a key fibromuscular node (injury can contribute to pelvic organ prolapse).

⚙️ Physiology

• Vaginal environment: usually acidic in reproductive years (typically pH ~3.8–4.5).
• Oestrogen effect: increases epithelial thickness and glycogen content.
• Lactobacilli metabolise glycogen → lactic acid → maintains acidity and inhibits pathogens.
• Lubrication: largely via plasma transudate during arousal plus cervical secretions; integrity depends on oestrogen and mucosal health.
• Mechanical roles: distensible canal allowing intercourse and childbirth; rugae and elastic tissue support expansion and recoil.

🔄 Changes Across the Lifespan

• Prepubertal: thin epithelium, neutral/alkaline pH, reduced lactobacilli → higher infection/irritation susceptibility.
• Reproductive years: oestrogenised thick mucosa, acidic pH, prominent rugae, robust microbiome.
• Postmenopausal: low oestrogen → thin fragile mucosa, reduced glycogen/lactobacilli, higher pH → dryness, dyspareunia, and vulnerability to inflammation/UTI symptoms (often termed GSM).

🩺 Clinical Correlates

• Speculum examination: uses the distensibility and fornices; posterior fornix relates to the pouch of Douglas (site for fluid collection).
• Infection defence: acidity and lactobacilli are central—antibiotics, semen (alkaline), bleeding, and low oestrogen can alter pH and microbiome.
• Trauma/bleeding: rich venous plexus + mucosal fragility in low oestrogen states can make bleeding more likely.
• Lymph drainage patterns help explain node involvement in malignancy and guide assessment.

🧠 Teaching Commentary (Makindo-style)

• Think of the vagina as a hormone-responsive, immunologically active mucosa: oestrogen thickens epithelium and loads it with glycogen, which “feeds” lactobacilli to maintain an acidic pH—this is a key reason infection patterns differ prepubertally and postmenopausally.
• The upper vs lower innervation split matters clinically: upper vagina pain is visceral (vague), while the lower third is pudendal (sharp/well localised), explaining why procedures at the introitus often need more targeted local anaesthesia.
• Remember there are no vaginal glands; most lubrication is transudate plus cervical/vestibular contributions—so low oestrogen states disproportionately cause dryness and microtrauma.