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The Uterus - Complete 10-Mark Study Notes

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1. GROSS ANATOMY

Parts of the Uterus

Position

• Normal position: Anteverted (long axis tilted forward relative to vagina) and Anteflexed (body bent forward at isthmus relative to cervix)

Ligaments (Support)

• Primary support = pelvic floor muscles (levator ani), supplemented by ligaments.

Blood Supply

• Uterine artery (branch of internal iliac artery) - main supply
• At the isthmus it crosses the ureter ("water under the bridge" - clinically important in hysterectomy)
• Ascending branch anastomoses with the ovarian artery
• Venous drainage: uterine venous plexus → internal iliac vein

Lymphatic Drainage

• Upper body/fundus → para-aortic nodes
• Lower body/cervix → iliac (external & internal) nodes, obturator nodes

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2. HISTOLOGY (Wall Layers)

a) Perimetrium (outer)

• Peritoneal serosa (mesothelium) covering most of uterus
• Adventitia on anterior-inferior surface

b) Myometrium (middle - thickest)

• Bundles of smooth muscle in interwoven layers
• Rich in venous plexuses and lymphatics
• During pregnancy: undergoes hyperplasia + hypertrophy + increased collagen to withstand parturition
• After delivery: smooth muscle cells shrink, many undergo apoptosis

c) Endometrium (inner mucosa)

• Lined by simple columnar epithelium (ciliated + secretory cells)
• Stroma: type III collagen, abundant fibroblasts
• Contains tubular uterine glands penetrating full thickness

Blood Vessels of Endometrium (Critical for Menstruation)

• Straight arteries - supply basal layer (NOT sensitive to progesterone withdrawal - why basal layer is retained)
• Spiral arteries - supply functional layer (sensitive to progesterone withdrawal → vasospasm → ischemia → menstrual shedding)

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3. PHYSIOLOGY - MENSTRUAL / UTERINE CYCLE

Phases of the Uterine Cycle

• Day 14: LH surge triggers ovulation
• If no implantation: corpus luteum regresses → progesterone falls → spiral artery spasm → menstruation
• Implantation of blastocyst occurs in the body of the uterus, normally on day 20-23

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4. PATHOLOGY (Diseases of the Uterus)

A. Endometritis

• Acute: bacterial, post-delivery/miscarriage; neutrophilic infiltrate
• Chronic: requires plasma cells for diagnosis (lymphocytes alone are normal); causes include PID (N. gonorrhoeae, C. trachomatis), tuberculosis (granulomatous endometritis)
• Features: fever, abdominal pain, menstrual irregularities

B. Adenomyosis

• Endometrial tissue (glands + stroma) present within the myometrium
• Induces reactive myometrial hypertrophy → enlarged, globular uterus
• Causes: menorrhagia, dysmenorrhea, pelvic pain (worse premenstrually)
• Can coexist with endometriosis

C. Endometriosis

• Endometrial glands + stroma outside the uterus
• Affects ~10% of women in reproductive years; ~50% with infertility
• Common sites: ovaries, pouch of Douglas, uterine ligaments, fallopian tubes
• Types: superficial peritoneal, ovarian (chocolate cysts), deep infiltrating
• Malignant transformation risk: mainly deep infiltrating type
• Pathogenesis theories:
  1. Regurgitation (retrograde menstruation) - most widely accepted
  2. Benign metastasis - via blood/lymphatics
  3. Metaplastic - from coelomic epithelium
  4. Stem/progenitor cell theory - bone marrow derived

D. Dysfunctional Uterine Bleeding (DUB)

• Abnormal uterine bleeding without organic cause
• Most common cause: anovulatory cycles (excess unopposed estrogen)
• Other causes: pituitary tumors (prolactin excess → reduced GnRH/LH/FSH), polycystic ovarian syndrome, obesity, luteal phase defect

E. Endometrial Hyperplasia

• Excess estrogen relative to progestin → exaggerated proliferation
• Causes: obesity (adipose converts precursors to estrogen), PCOS, granulosa-theca cell tumors, exogenous estrogen

• Treatment with atypia: hysterectomy (or high-dose progestins if fertility desired)

F. Endometrial Carcinoma

• Most common gynecologic malignancy
• Presents with postmenopausal bleeding (most common symptom)
• Two main types:
  • Type I (endometrioid): Estrogen-related, arises from hyperplasia/EIN, PTEN mutations, better prognosis
  • Type II (serous/clear cell): Not estrogen-related, TP53 mutations, worse prognosis

G. Leiomyoma (Fibroid)

• Most common uterine tumor; benign smooth muscle tumor of myometrium
• Estrogen-dependent; regress after menopause
• Presents with: menorrhagia, pelvic pain, pressure symptoms, infertility
• Malignant transformation to leiomyosarcoma is rare

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5. EMBRYOLOGY (Development)

• Uterus develops from fusion of the paramesonephric (Mullerian) ducts
• In females: absence of Y chromosome, testosterone, and anti-Mullerian hormone → Mullerian ducts become dominant
• Incomplete fusion or failure of resorption leads to uterine anomalies (bicornuate, septate, unicornuate, didelphys uterus)

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6. CLINICAL POINTS (For Exam MCQs/Short Notes)

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UTERUS - Complete Exam Notes (10 Marks)

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1. FEATURES

Size & Weight

• Length: ~8 cm | Width: ~5 cm | Thickness: ~4 cm
• Weight: ~60-80 g (nulliparous), ~100 g (parous)

Parts

Normal Position

• Anteverted - long axis of uterus tilted forward relative to vagina (most common)
• Anteflexed - body bent forward at the isthmus relative to cervix

Wall Layers (3)

1. Perimetrium - outer serosal/peritoneal covering
2. Myometrium - thick smooth muscle (thickest layer); undergoes hyperplasia + hypertrophy in pregnancy
3. Endometrium - inner mucosa; simple columnar epithelium; has functional layer (shed in menstruation) and basal layer (retained, regenerates)

Relations

• Anterior: Vesicouterine pouch + bladder
• Posterior: Rectouterine pouch (pouch of Douglas) + rectum
• Lateral: Broad ligament, uterine vessels, ureter
• Inferior: Vagina

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2. BLOOD SUPPLY

Arterial Supply

1. Runs in subperitoneal connective tissue
2. Passes over the ureter at the base of the broad ligament (~1.5-2 cm lateral to the cervix)
3. Reaches the lateral uterine wall near the cervix
4. Divides into:
   • Ascending branch - runs tortuously along the lateral wall → anastomoses with ovarian artery at the fundus; gives a tubal branch
   • Descending branch (vaginal artery) - supplies cervix and upper vagina

• Ovarian artery (branch of abdominal aorta) - anastomoses with ascending uterine artery at fundus

Venous Drainage

• Uterine venous plexus (valveless network around body and cervix, located in parametrium) → uterine veins → internal iliac veins

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3. NERVE SUPPLY

Source

• Inferior hypogastric plexus (pelvic plexus) + pelvic splanchnic nerves (S2-S4)
• These form the uterovaginal plexus (Frankenhäuser ganglion) - large ganglion cells located lateral to the cervix

Sympathetic (T10-L1)

• Via inferior hypogastric plexus
• Causes uterine contraction and vasoconstriction

Parasympathetic (S2-S4)

• Via pelvic splanchnic nerves
• Causes uterine relaxation and vasodilation

Pain Referral

• Uterine body pain - referred to T10-L1 dermatomes (umbilicus and groin)
• Cervical pain - referred to S2-S4 dermatomes (perineum, inner thigh)

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4. SUPPORTS OF THE UTERUS ⭐ (Most Asked)

A. MAIN LIGAMENTS

B. SECONDARY SUPPORT (condensations of endopelvic fascia)

• Parametrium (tissue around uterus/cervix)
• Perineal body
• Urogenital diaphragm

KEY EXAM POINT:

The cardinal (Mackenrodt's) ligament is the most important ligament support of the uterus. Damage to it (during childbirth) leads to uterine prolapse. The uterosacral ligament maintains anteversion and its damage causes retroversion.

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5. LYMPHATIC DRAINAGE ⭐ (Most Asked)

Summary Diagram (Memory Aid)

FUNDUS ──────────────────────────────► Para-aortic nodes (main)
FUNDUS (via round lig.) ─────────────► Superficial inguinal nodes
BODY (via broad lig.) ───────────────► External/Common iliac nodes
CERVIX ──────────────────────────────► Internal iliac + Obturator + Sacral nodes

KEY EXAM POINT:

Para-aortic nodes are the primary nodes for the uterine fundus/body. The cervix drains to iliac nodes (internal + external + obturator + sacral). Sentinel node for cervical cancer = obturator node

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6. APPLIED ANATOMY (Clinical Significance)

1. Uterine Artery - Ureter Relationship ("Water Under the Bridge")

• The uterine artery passes over the ureter at the base of the broad ligament (~1.5-2 cm lateral to the cervix)
• Mnemonic: "Water (ureter) under the bridge (uterine artery)"
• Clinical risk: During hysterectomy or ligation of uterine artery, the ureter can be accidentally cut or ligated
• Always identify the ureter before clamping the uterine artery

2. Uterine Prolapse

• Caused by damage to cardinal ligament + levator ani (most common after difficult childbirth)
• Types: 1st degree (cervix in vagina), 2nd degree (cervix at introitus), 3rd degree / procidentia (uterus outside vulva)
• Treatment: Pelvic floor exercises (mild), ring pessary, surgical repair (Manchester repair / hysterectomy)

3. Hysterectomy

• Surgical removal of uterus
• Main risk: Ureteric injury at the uterine artery ligation point
• Total abdominal hysterectomy (TAH) = body + fundus + cervix removed
• Radical hysterectomy (Wertheim's) = TAH + parametrium + upper vagina + pelvic nodes (for cervical cancer)

4. Carcinoma of Uterus / Cervix - Spread

• Spreads via lymphatics → internal and common iliac nodes, sacral nodes
• Can also spread via veins (lung metastases) and directly to bladder/rectum

5. Ectopic Pregnancy (Tubal)

• Blastocyst implants outside the uterus (most common: fallopian tube)
• Normal implantation: body of uterus (posterior wall near fundus, day 20-23)
• Uterine artery ligation may be used to control postpartum hemorrhage (PPH)

6. Lower Uterine Segment (LUS)

• Formed by the isthmus during pregnancy
• Site of lower segment cesarean section (LSCS) incision - less vascular, heals better
• Location of placenta previa if placenta implants here

7. Frankenhäuser's Ganglion Block

• Block of uterovaginal plexus (lateral to cervix) used in paracervical block for pain relief during labor or gynecological procedures

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