Female Pelvic Anatomy and Embryogenesis

Vascular Supply of the Pelvis

The pelvic organs receive their blood supply primarily from branches of the internal iliac arteries. These arteries are divided into two main branches:

1. Anterior Division: This division is highly branched and supplies most of the pelvic viscera. It gives rise to the:
   • Umbilical artery
   • Uterine artery
   • Superior vesical artery
   • Vaginal artery
   • Obturator artery
   • Middle rectal artery
   • Internal pudendal artery
   • Inferior gluteal artery
2. Posterior Division: This division primarily supplies the pelvic wall and gluteal region, giving rise to the:
   • Iliolumbar artery
   • Lateral sacral arteries
   • Superior gluteal artery

External Genitalia and the Perineum

The external female genitalia, collectively known as the vulva, consist of several distinct structures that serve reproductive and sensory functions.

• Labia Majora: Large, outer folds of skin containing adipose tissue, which fuse anteriorly with the mons pubis and posteriorly at the perineum.
• Labia Minora: Thinner, narrow skin folds located inside the labia majora.
• Clitoris: An erectile tissue structure consisting of the glans and two crura.
• Vestibule: The area containing the openings of the vagina and the ducts of the glands that open into it.
• Perineum: The anatomical region located between the vaginal opening and the buttocks.

Clinical Note: Bartholin Cyst Abscess The Bartholin glands open into the vestibule. If the duct of a Bartholin gland becomes obstructed, fluid can accumulate, forming a cyst. If this cyst becomes infected, it results in a painful Bartholin cyst abscess.

Embryogenesis: The Ovary and External Genitalia

The complex structures of the female reproductive system arise from highly regulated developmental stages during the fetal period.

Ovarian Development

The development of the ovary involves the interaction between germ cells and somatic cells:

1. Cortical Cord Formation: In the early fetal period, mesothelial cells on the surface of the gonad form cortical cords that invade the periphery of the medulla.
2. Oogonia Differentiation: By approximately week 16, these cortical cords surround primordial germ cells. These cells differentiate into oogonia, which proliferate via mitosis.
3. Meiotic Arrest: The oogonia enter the first meiotic division to become primary oocytes.
4. Primordial Follicle Formation: The primary oocyte secretes factors that induce surrounding squamous cells to differentiate into follicular cells. The combination of a primary oocyte and these surrounding follicular cells forms a primordial follicle.

External Genitalia Development

The development of the external genitalia begins during the 3rd week of gestation through the differentiation of the cloacal fold:

• Genital Tubercle: The cranial portion of the folds unites to form the genital tubercle, which becomes the primordial phallus.
• Urethral and Anal Folds: The folds divide caudally into the urethral folds (surrounding the developing urinary system) and the anal fold (surrounding the anus).
• Genital (Labioscrotal) Swellings: Lateral to the cloacal fold, these swellings develop into the labia in females (or the scrotum in males).