The Uterus

1. Position and Relations

2. Parts of the Uterus

• The uterine cavity is a narrow slit when viewed laterally, and an inverted triangle when viewed anteriorly.
• Each superior corner of the cavity (the cornua) opens into a uterine tube; the inferior corner leads into the cervical canal.
• Implantation of the blastocyst normally occurs in the body. - Gray's Anatomy for Students

3. Wall Layers (3 Layers)

A. Perimetrium (Serosa)

• Outermost layer; a thin peritoneal covering continuous with the broad ligaments and pelvic peritoneum.

B. Myometrium

• The thickest layer; composed of smooth muscle arranged in three distinct sublayers:
  • Inner (subvascular) layer - thin
  • Middle layer - thickest; rich vascular supply (sponge-like); muscle cells form a 3D meshwork. This is the main layer responsible for expelling the fetus during birth.
  • Outer (supravascular) layer - thin

Clinical note: During pregnancy, smooth muscle cells enlarge, allowing the uterus to grow 7-10x its original size. Benign tumors of myometrium are called leiomyomas (fibroids). - Color Atlas of Human Anatomy

C. Endometrium (Mucosa)

• The innermost layer lining the uterine cavity.
• Cell-rich connective tissue with simple columnar epithelium.
• Contains uterine glands (tubular invaginations).
• Divided into two layers:
  • Basalis (Basal layer) - not shed during menstruation; regenerates the endometrium each cycle.
  • Functionalis (Functional layer) - undergoes cyclic changes; shed during menstruation.

• Proliferative phase (Days 5-14): Functional layer restored under estradiol influence; glands enlarge.
• Secretory phase (Days 15-28): Glands continue growing under progesterone + estrogen; produce viscous secretion; blood vessels multiply. Spongy layer (II) and compact layer (III) become distinct.
• Ischemic/Desquamation phase (Days 1-4): Hormone withdrawal causes tissue degeneration and shedding (menstruation). - Color Atlas of Human Anatomy

Clinical note: Curettage removes only the functional layer, leaving the basal layer intact. When endometrial tissue migrates outside the uterine cavity to the ovary or pelvic peritoneum, the result is endometriosis. - Color Atlas of Human Anatomy

4. Cervix - Special Features

• The cervical mucosa does NOT undergo cyclic shedding.
• Has branching tubular cervical glands that produce alkaline mucus.
• Ectocervix (vaginal portion): covered by stratified non-keratinized squamous epithelium.
• Endocervical canal: lined by columnar epithelium.
• The junction between the two is the Squamo-columnar junction (transformation zone).

Clinical note: The transformation zone is the most common site of cervical carcinoma. It is visible on colposcopy in women of childbearing age, but migrates into the cervical canal with increasing age. - Color Atlas of Human Anatomy

5. Ligaments of the Uterus

Note: Of all these, anatomically only the round ligament and broad ligament are clearly defined structures. The uterus is mainly supported by the pelvic floor muscles, not the ligaments. - Color Atlas of Human Anatomy, Sabiston Textbook of Surgery

6. Blood Supply

• Uterine arteries - branches of the internal iliac arteries; travel within the cardinal ligament then superiorly along the lateral uterine body.
• Ovarian arteries - arise directly from the abdominal aorta; travel to the uterus adjacent to the ovary.

Clinical note: During hysterectomy, the distal ureters must be carefully identified because the uterine arteries pass very close to them (the ureter is at risk of ligation). - Gray's Anatomy for Students

7. Nerve Supply

8. Clinical Correlates Summary

Rectus Sheath - Short Notes

Definition

Formation - Key Rule

Composition (The Most Important Table in Anatomy)

The Arcuate Line (Line of Douglas)

• Located midway between the umbilicus and pubic symphysis.
• Marks where all aponeuroses shift anterior to the rectus muscle.
• Below this line, the posterior wall is absent - rectus abdominis lies directly on transversalis fascia.
• The aponeurotic fibers do not end abruptly; they attenuate gradually. - Mulholland & Greenfield's Surgery

External Surface Landmarks

1. Semilunar line (Spighelian line) - curved depression along the lateral border of the rectus sheath; marks where lateral aponeuroses begin.
2. Tendinous inscriptions - 3 fibrous bands crossing the rectus abdominis, creating the "six-pack" appearance.
3. Linea alba - midline confluence of right and left aponeuroses of both sides.

Contents of the Rectus Sheath

The superior and inferior epigastric arteries enter the rectus sheath and anastomose near the umbilicus, forming an important collateral pathway. - Mulholland & Greenfield's Surgery

Blood Supply - Clinical Importance

• Superior epigastric artery = terminal branch of internal thoracic (internal mammary) artery
• Inferior epigastric artery = branch of external iliac artery
• Both enter the sheath and anastomose near the umbilicus
• This anastomosis is used in TRAM flap (Transverse Rectus Abdominis Myocutaneous flap) for breast reconstruction

Nerve Supply

• Lower intercostal nerves T7-T12 and L1, L2 (iliohypogastric, ilioinguinal)
• Nerves travel in the plane between internal oblique and transversus abdominis, then pierce the lateral aspect of the sheath.

Clinical Correlates

1. Rectus Sheath Hematoma

• Caused by rupture of epigastric vessels (superior or inferior) within the sheath.
• Can follow trauma, vigorous coughing, anticoagulation, or pregnancy.
• Key sign: Tender abdominal wall mass that does not cross the midline and remains palpable when rectus is contracted (Fothergill's sign - distinguishes it from intraperitoneal masses).
• Above arcuate line: hematoma is contained (cannot spread across midline).
• Below arcuate line: no posterior sheath - hematoma may spread freely into pelvic extraperitoneal space.
• Treatment: Hemodynamically stable + small = conservative (bed rest, ice, analgesia). Unstable or expanding = arterial embolization or surgical evacuation. - Schwartz's Principles of Surgery; Sabiston Textbook

2. Diastasis Recti

• Abnormal separation of the two rectus muscles (>2 cm) at the linea alba.
• NOT a true hernia (fascia intact; no risk of strangulation).
• Common in pregnancy, obesity, connective tissue disorders.
• Presents as fusiform midline bulge worsening with Valsalva.
• Management: conservative (weight loss, exercise); surgery only for functional disability or cosmesis. - Schwartz's Principles of Surgery

3. Rectus Sheath Block (Regional Anesthesia)

• Local anesthetic injected into the posterior rectus sheath space bilaterally.
• Blocks T9-T11 (periumbilical analgesia).
• Used for umbilical hernia repair and midline laparotomy analgesia.

4. TRAM Flap / DIEP Flap

• Rectus abdominis with its blood supply (inferior epigastric vessels) used for breast reconstruction.
• Deep Inferior Epigastric Perforator (DIEP) flap spares the muscle.

5. Spighelian Hernia

• Hernia through the semilunar line (lateral border of rectus sheath), usually just below the arcuate line where the posterior sheath is absent.
• Can be difficult to detect clinically as it may be covered by the external oblique aponeurosis.

Summary Mnemonic for Sheath Composition