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