Overview
The uterus is a hollow, pear-shaped, thick-walled muscular organ in the female pelvis, located between the bladder (anteriorly) and rectum (posteriorly). It is essential for menstruation, implantation, pregnancy, and labor.
Anatomical Position
- Normal position: Anteverted and anteflexed
- Anteversion: angle between cervix and vagina (~90°, opening anteriorly)
- Anteflexion: angle between cervix and body of uterus (~170°)
- Position variations: Retroverted uterus occurs in ~20-30% of women (usually asymptomatic)
Anatomical Regions
- Fundus: Dome-shaped superior portion above the entry of the uterine tubes
- Body (corpus): Main central portion
- Isthmus: Narrowed transition between body and cervix (~1 cm long)
- Cervix: Inferior cylindrical portion projecting into the vagina
Layers of the Uterine Wall
- Perimetrium: Outer serous layer (peritoneum)
- Myometrium: Thick smooth muscle layer; the layer that contracts during labor and menstruation
- Endometrium: Inner mucosal layer that sloughs during menstruation and proliferates during the cycle
- Functional layer: Sloughs during menstruation
- Basal layer: Retained, regenerates the functional layer each cycle
Ligamentous Supports
Primary Supports
- Transverse cervical (cardinal) ligaments: Most important support; contain the uterine vessels; extend from cervix to pelvic side walls
- Uterosacral ligaments: From cervix to sacrum; resist posterior displacement
Secondary Supports
- Round ligaments: Maintain anteflexion; pass through the inguinal canal to the labia majora (homologue of gubernaculum testis)
- Broad ligaments: Double folds of peritoneum extending from uterus to lateral pelvic walls; contain the uterine tubes, ovaries (via mesovarium), round ligaments, and uterine vessels
- Pubocervical fascia: Supports anteriorly; prevents cystocele
- Uterovesical and rectovaginal fascia: Additional pelvic support
Blood Supply
- Uterine artery (branch of internal iliac): Main supply
- Ovarian artery (from abdominal aorta): Anastomoses with uterine artery; supplies the fundus and tubes
Clinical pearl: The ureter passes UNDER the uterine artery ("water under the bridge") at the lateral fornix — a critical relationship during hysterectomy to avoid iatrogenic ureteral injury.
Lymphatic Drainage
- Fundus and upper body: Para-aortic nodes (along ovarian vessels)
- Lower body: External iliac nodes
- Cervix: External iliac, internal iliac (hypogastric), and obturator nodes
- Clinical relevance: Cervical cancer staging requires sentinel node biopsy mapping
Clinical Correlations
Fibroids (Leiomyomas)
- Benign smooth muscle tumors; most common pelvic tumor in women
- Classified by location:
- Submucosal: Project into the uterine cavity (cause menorrhagia)
- Intramural: Within the myometrium (most common)
- Subserosal: Project outward (may compress bladder or ureter)
Uterine Prolapse
- Descent of the uterus into the vagina due to weakened pelvic floor supports
- Risk factors: Multiparity, vaginal delivery, obesity, age, chronic constipation
- Staging (Pelvic Organ Prolapse Quantification, POP-Q):
- Stage 0: No prolapse
- Stage I: Cervix descends but remains in vagina
- Stage II: Cervix reaches introitus
- Stage III: Cervix protrudes beyond introitus
- Stage IV: Complete prolapse (procidentia)
Endometriosis
- Functional endometrial tissue outside the uterine cavity
- Common sites: Ovaries (chocolate cysts), uterosacral ligaments, rectovaginal septum, peritoneal surfaces
- Symptoms: Dysmenorrhea, dyspareunia, dyschezia, infertility
Adenomyosis
- Endometrial glands within the myometrium
- Causes heavy painful periods and enlarged, boggy, tender uterus
- Diagnosed definitively only on histology after hysterectomy
Endometrial Cancer
- Most common gynecologic malignancy in developed countries
- Type I (estrogen-driven, endometrioid): Associated with unopposed estrogen, obesity, PCOS, late menopause; better prognosis
- Type II (serous, clear cell): Aggressive, p53 mutations, poor prognosis
- Postmenopausal bleeding is the cardinal symptom
Key Takeaway
The uterus's anteverted/anteflexed position, layered muscular wall, and dual blood supply make it uniquely suited for pregnancy. Remember: uterine artery OVER ureter ("bridge over water"), cardinal and uterosacral ligaments as primary supports, and the clinical triad of fibroids/prolapse/endometriosis for exam questions.