Topographic anatomy of the female pelvis (draw sagittal section), mechanism of continence

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Introduction

The female pelvis is a complex anatomical region housing vital organs of the urinary, reproductive, and digestive systems. Understanding its topography is essential for clinical practice in gynecology, urology, and colorectal surgery. This article covers the sagittal topography of pelvic organs and the mechanism of urinary and fecal continence, all grounded in clinically relevant anatomy.

1. General Topography of the Female Pelvis

The female pelvis is divided into the greater (false) pelvis and the lesser (true) pelvis. The true pelvis lies below the pelvic brim and contains the pelvic organs.

In the median sagittal section, from anterior to posterior, the topographic anatomy is as follows:

  1. Pubic symphysis – anterior boundary of the pelvic cavity
  2. Urinary bladder – lies just posterior to the pubic symphysis; in its empty state, entirely within the pelvis
  3. Urethra – extends from the bladder neck, passes inferiorly through the pelvic floor
  4. Vagina – lies posterior to the urethra and bladder
  5. Uterus – positioned above the vagina, between bladder and rectum; in anteverted and anteflexed position in most women
  6. Rectum – lies posterior to the vagina and uterus
  7. Sacrum and coccyx – posterior boundary

The peritoneum drapes over the pelvic organs, creating pouches:

  • Vesicouterine pouch – between bladder and uterus
  • Rectouterine pouch (pouch of Douglas) – between uterus and rectum, the deepest point of the peritoneal cavity in females

2. Pelvic Floor and Its Role in Organ Support

The pelvic organs are supported by:

  • Pelvic bones and ligaments
  • Pelvic diaphragm – mainly formed by the levator ani (puborectalis, pubococcygeus, iliococcygeus) and coccygeus muscles
  • Urogenital diaphragm – includes deep transverse perineal muscles and sphincters
  • Perineal body – a central tendon of the perineum where several muscles converge; critical for support

These muscular and fascial structures form the pelvic floor, maintaining organ position and playing a crucial role in continence.

3. Mechanism of Continence

Continence refers to the ability to voluntarily retain urine and feces, relying on intact neuromuscular coordination and structural support.

Urinary Continence

Urinary continence is primarily maintained by:

  • Internal urethral sphincter (smooth muscle at bladder neck): involuntary control, under sympathetic regulation
  • External urethral sphincter (striated muscle in the deep perineal pouch): voluntary control, innervated by the pudendal nerve
  • Pelvic floor muscles, especially levator ani, which provide support to the bladder neck and urethra
  • The angle between the bladder and urethra (urethrovesical angle) contributes to passive closure

During activities that increase intra-abdominal pressure (e.g. coughing, sneezing), the levator ani contracts reflexively to compress the urethra against the pubic symphysis, preventing urine leakage. This is crucial in maintaining stress continence.

Fecal Continence

Fecal continence depends on:

  • Internal anal sphincter (smooth muscle): involuntary tone maintained by the sympathetic nervous system
  • External anal sphincter (striated muscle): voluntary control via the inferior rectal branch of the pudendal nerve
  • Puborectalis muscle (part of levator ani): forms a sling around the rectoanal junction; maintains the anorectal angle (~80°), which acts as a mechanical barrier

Voluntary control over defecation is achieved by conscious contraction of the external anal sphincter and puborectalis, resisting the urge to defecate until appropriate. Loss of tone in any of these structures, or nerve damage, may result in incontinence.

4. Labeled Sagittal Section: Female Pelvis

You should draw or refer to a median sagittal section (midline cut) of the female pelvis, which clearly displays the organs in order from anterior to posterior.

Structures to include (from front to back):

  • Pubic symphysis
  • Urinary bladder
  • Urethra
  • Vagina
  • Cervix and uterus (anteverted, anteflexed)
  • Rectum
  • Anal canal
  • Sacrum and coccyx
  • Peritoneal reflections: vesicouterine and rectouterine pouches
  • Pelvic diaphragm with levator ani

(Use diagrams from Sobotta Atlas or Gray’s Anatomy to ensure accuracy and compliance with university standards.)

Conclusion

The female pelvis contains densely packed organs with complex relationships. Understanding the spatial organization of these organs and the muscular support system is essential for interpreting pelvic floor dysfunctions, continence mechanisms, and for guiding surgical or diagnostic procedures.

References

  1. Paulsen, F., Waschke, J. Sobotta Atlas of Human Anatomy, Vol. 2, 16th ed. Elsevier.
  2. Drake, R.L., Vogl, A.W., Mitchell, A.W.M. Gray’s Anatomy for Students, 4th ed. Elsevier.
  3. Moore, K.L., Dalley, A.F., Agur, A.M.R. Clinically Oriented Anatomy, 8th ed. Wolters Kluwer.
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