3.5 The Pelvic Viscera
Key Takeaways
- The urinary bladder lies retro pubically behind the pubic symphysis; in males it rests on the prostate and seminal vesicles, in females on the anterior vaginal wall and cervix; its mucosa is smooth except over the trigone where it is fixed.
- The male pelvic viscera include the prostate (three zones: peripheral, central, transitional — cancers arise peripherally, benign prostatic hyperplasia in the transitional zone), seminal vesicles (secrete fructose-rich fluid), and the terminal ductus (vas) deferens forming the ejaculatory duct with the seminal vesicle duct.
- The female pelvic viscera include the uterus (anteflexed and anteverted in most women), paired ovaries and uterine tubes, and the vagina; the broad ligament is a peritoneal fold enclosing the tubes, ovaries, and round ligaments.
- Peritoneal relationships differ by sex: in males the rectovesical pouch is the lowest point; in females the rectouterine pouch (of Douglas) and vesicouterine pouch exist, with the rectouterine pouch the most dependent space for fluid accumulation.
- Pelvic viscera receive sympathetic (T10–L2) and parasympathetic (S2–S4 via pelvic splanchnic nerves) supply; the pudendal nerve (S2–S4) provides somatic innervation to the perineum and external sphincters.
Urinary Bladder
Quick Answer: The urinary bladder is a retro-pubic, distensible reservoir with a smooth mucosa except over the trigone, where it is fixed. In males it lies on the prostate and seminal vesicles; in females on the anterior vaginal wall and cervix. The detrusor muscle is the smooth muscle wall; the internal urethral sphincter (smooth muscle, autonomic) and external urethral sphincter (skeletal muscle, pudendal nerve) govern continence.
Bladder Anatomy and Relations
- Apex — points toward the pubic symphysis; the urachus (median umbilical ligament) is its remnant.
- Body — the major distensible portion.
- Base (fundus) — posteriorinferior; in males related to the prostate, seminal vesicles, and rectum (separated by the rectovesical pouch and Denonvilliers fascia); in females related to the anterior vaginal wall and cervix (separated by the vesicouterine pouch).
- Neck — lowest part, continuous with the urethra.
The trigone is the smooth triangular area between the two ureteric orifices and the internal urethral meatus; it is embryologically derived from the mesonephric duct (unlike the rest of the bladder, which is endodermal) and is the site where ureteric jets are seen on cystoscopy.
Micturition
Parasympathetic pelvic splanchnic nerves (S2–S4) contract the detrusor and relax the internal sphincter (via M3 receptors); sympathetic hypogastric nerves (T11–L2) relax the detrusor and contract the internal sphincter (during ejaculation in males, preventing retrograde ejaculation). The pudendal nerve (S2–S4, somatic) supplies the external urethral sphincter.
Rectum
The rectum is the terminal ~15 cm of the large intestine, lying anterior to the sacrum and coccyx. It lacks taeniae coli, haustra, and epiploic appendages (transitions at the rectosigmoid junction). The anal canal begins at the pelvic floor (puborectalis sling → anorectal angle).
- Upper anal canal (above pectinate line) — derived from endoderm; supplied by superior rectal artery (continuation of inferior mesenteric); lymphatics drain to inferior mesenteric and para-aortic nodes; sensation is visceral (autonomic).
- Lower anal canal (below pectinate line) — derived from ectoderm; supplied by inferior rectal artery (branch of internal pudendal); lymphatics drain to superficial inguinal nodes; sensation is somatic via the inferior rectal nerve (branch of pudendal).
The pectinate line marks the embryologic boundary and is the anatomic explanation for differences in pain sensation, vascular supply, and lymphatic drainage between internal (painless) and external (painful) hemorrhoids.
Male Pelvic Viscera
Prostate Gland
The prostate lies inferior to the bladder neck and surrounds the proximal urethra (prostatic urethra). It is a fibromuscular glandular organ shaped like a walnut (~20 g), with three anatomically and clinically distinct zones:
| Zone | Location | Clinical Significance |
|---|---|---|
| Peripheral zone | Posterior and lateral (palpable on DRE) | Site of ~70–80% of prostate cancers |
| Central zone | Around ejaculatory ducts | Rare site of cancer |
| Transitional zone | surrounds proximal urethra | Site of benign prostatic hyperplasia (BPH) causing urinary obstruction |
The prostatic urethra receives the ejaculatory ducts (formed by the union of the ductus deferens and the seminal vesicle duct) at the verumontanum.
Seminal Vesicles and Ductus Deferens
- Seminal vesicles — paired, lie posterior to the bladder; secrete an alkaline, fructose-rich fluid that constitutes ~70% of ejaculate volume. They do not store sperm.
- Ductus (vas) deferens — transports sperm from the epididymis through the inguinal canal to the pelvic cavity; it passes superior to the ureter ("water under the bridge") and dilates into the ampulla before joining the seminal vesicle duct to form the ejaculatory duct.
Male Peritoneal Relationships
The lowest peritoneal recess in males is the rectovesical pouch, between the rectum and bladder. Fluid, blood, or pus in the abdomen accumulates here first when a man is upright.
Female Pelvic Viscera
Uterus
The uterus is a thick-walled muscular organ (~7–8 cm long in the non-pregnant adult) divided into fundus, body, isthmus, and cervix. Most women have an anteverted (cervix points posteriorly, body anteriorly over the bladder) and anteflexed (fundus bent forward on the body) uterus. Retroversion is a normal variant but can be associated with endometriosis and dyspareunia.
Supporting ligaments:
- Broad ligament — peritoneal fold enclosing the uterine tubes, ovaries, round ligaments, and uterine vessels; not a true weight-bearing ligament.
- Round ligament — extends from the uterus through the inguinal canal to the labia majora; maintains anteflexion.
- Transverse cervical (cardinal) ligament — strong connective tissue at the cervix; key support preventing uterine prolapse.
- Uterosacral ligaments — extend from cervix to sacrum; maintain the cervix in its normal posterior position.
Ovaries and Uterine Tubes
- Ovaries — paired, almond-shaped, lie on the posterior pelvic wall in the ovarian fossa; supplied by the ovarian artery (direct branch of the aorta) and ovarian vein (right → IVC; left → left renal vein). Lymphatics drain to para-aortic nodes.
- Uterine (fallopian) tubes — ~10 cm long, divided into interstitial, isthmus, ampulla (site of fertilization), and fimbriated infundibulum. The tube is supplied by the uterine and ovarian arteries.
Vagina
The vagina is a fibromuscular tube (~8–10 cm) extending from the cervix to the vestibule, posterior to the bladder and urethra and anterior to the rectum. The fornices surround the cervix; the posterior fornix is deeper and related to the rectouterine pouch of Douglas — an important clinical site for culdocentesis and transvaginal ultrasound.
Female Peritoneal Relationships
Two peritoneal pouches exist in females: the vesicouterine pouch (between bladder and uterus) and the rectouterine pouch (of Douglas) (between uterus and rectum). The latter is the most dependent point in the female peritoneal cavity when upright and is where intraperitoneal fluid, blood, or pus accumulates.
Vascular and Nerve Supply of Pelvic Viscera
| Viscera | Arterial Supply | Sympathetic | Parasympathetic |
|---|---|---|---|
| Bladder | Superior and inferior vesical arteries (internal iliac) | T11–L2 (hypogastric) → relax detrusor, contract internal sphincter | S2–S4 (pelvic splanchnic) → contract detrusor, relax internal sphincter |
| Rectum (upper) | Superior rectal (IMA) | Lumbar splanchnics | Pelvic splanchnics |
| Rectum (lower) | Middle and inferior rectal (internal iliac and internal pudendal) | Hypogastric | Pelvic splanchnic + pudendal (somatic) |
| Prostate/Seminal vesicles | Inferior vesical, middle rectal | Hypogastric (T11–L2) → emission | Pelvic splanchnic → erection |
| Uterus | Uterine artery (internal iliac) | Hypogastric | Pelvic splanchnic |
| Ovaries | Ovarian artery (aorta) | T10–T11 (lesser splanchnic) | Pelvic splanchnic |
The pudendal nerve (S2–S4, ventral rami) exits the pelvis through the greater sciatic foramen below piriformis, hooks around the sacrospinous ligament near the ischial spine, and re-enters through the lesser sciatic foramen into the pudendal (Alcock's) canal. It supplies the perineum, external anal and urethral sphincters, and skin of the external genitalia.
In which zone of the prostate does benign prostatic hyperplasia (BPH) typically arise, and which zone is the most common site of prostate adenocarcinoma?
A 38-year-old woman with a ruptured ectopic pregnancy is taken to surgery. In which peritoneal recess does free blood most predictably accumulate when the patient is supine, and which surgical approach accesses it most directly?