vas deferens

**Anatomy/Course:** Continuation of the tail of the epididymis → ascends in the spermatic cord (posterior to the other cord structures) → passes through the superficial inguinal ring, inguinal canal, and deep inguinal ring → crosses lateral pelvic wall, loops over the ureter (anterior to the ureter near the bladder; "water under the bridge" – ureter passes beneath the vas/uterine artery) → dilates to form the ampulla posterior to the bladder → joins the duct of the seminal vesicle to form the ejaculatory duct → traverses the prostate → empties into the prostatic urethra at the verumontanum (seminal colliculus).

**Embryology:** Derived from the mesonephric (Wolffian) duct, as are the epididymis, seminal vesicles, ejaculatory duct (mnemonic: SEED – Seminal vesicles, Epididymis, Ejaculatory duct, Ductus deferens). Differentiation depends on testosterone (from fetal Leydig cells). Müllerian-inhibiting substance (AMH) from Sertoli cells causes regression of the paramesonephric (Müllerian) duct. Without testosterone (e.g., in complete androgen insensitivity), Wolffian derivatives regress.

**Histology/Physiology:** Pseudostratified columnar epithelium with stereocilia, surrounded by a thick three-layered smooth muscle wall (inner longitudinal, middle circular, outer longitudinal). Sympathetic innervation (hypogastric nerve, T10–L2) causes peristalsis during **emission**. Point and shoot: Sympathetic = emission (vas, seminal vesicles, prostate); Visceral/somatic (pudendal nerve, S2–S4) = **ejaculation** (bulbospongiosus contraction); Parasympathetic (S2–S4, pelvic splanchnic) = erection. Sperm account for only ~5% of semen volume; most fluid comes from seminal vesicles (~60-70%) and prostate (~20-30%).

**Clinical correlations:** - **Vasectomy:** Bilateral ligation/excision of the vas; sterilization with no change in testosterone, libido, erection, or ejaculation (ejaculate volume is similar). Not immediately effective—requires clearance of stored sperm (~20 ejaculations/~3 months) and confirmation with semen analysis showing azoospermia. Complications: hematoma, sperm granuloma, post-vasectomy pain syndrome, anti-sperm antibodies (may reduce success of reversal). - **Congenital bilateral absence of the vas deferens (CBAVD):** Associated with CFTR mutations (cystic fibrosis; ~98% of men with CF are infertile). Presents as obstructive azoospermia with low semen volume, acidic pH, and low fructose (seminal vesicles often also hypoplastic/absent). Testicular size and FSH are normal, spermatogenesis intact; sperm can be retrieved by testicular/epididymal aspiration for IVF/ICSI. Often accompanied by unilateral renal agenesis in unilateral CAVD (shared Wolffian duct origin). - **Indirect inguinal hernia:** Sac travels within the spermatic cord alongside the vas, lateral to the inferior epigastric vessels (via deep inguinal ring). Hernia repair can injure the vas. - **Blood supply:** Artery to the ductus deferens (from the inferior vesical artery, branch of the anterior division of the internal iliac). Testicular artery (aorta) supplies the testis; cremasteric artery (inferior epigastric) supplies cremaster. - **Infection/inflammation:** Epididymitis/deferentitis (Chlamydia/Gonorrhea in men <35; E. coli in older men/children with urinary tract abnormalities). Tuberculosis can cause a "beaded" vas. - **Spermatic cord contents (mnemonic):** 3 arteries (testicular, cremasteric, artery to ductus deferens), 3 nerves (genital branch of genitofemoral, ilioinguinal [outside cord], sympathetic fibers), 3 other (vas, pampiniform plexus, lymphatics/processus vaginalis remnant). Layers derived from: external spermatic fascia (external oblique), cremasteric fascia/muscle (internal oblique), internal spermatic fascia (transversalis fascia).

**High-yield pearls:** Vas = Wolffian; ureter lies posterior to vas near the bladder (risk of ureteral injury during ligation of vas/uterine artery); the sole contents of the spermatic cord that are palpable as a firm "cord" is the vas; Kartagener syndrome causes infertility due to immotile sperm (normal anatomy, abnormal dynein), unlike CBAVD.