ductus deferens

**Anatomy/course:** Continuation of the tail of the epididymis. Ascends in the spermatic cord (posterior to the other cord structures) -> through the superficial inguinal ring, inguinal canal, and deep inguinal ring -> crosses over the external iliac vessels -> passes medially over the ureter ("water under the bridge": the ductus deferens passes anterior/superior to the ureter) -> descends behind the bladder -> dilates into the ampulla -> joins the duct of the seminal vesicle to form the ejaculatory duct, which traverses the prostate and opens into the prostatic urethra at the verumontanum (seminal colliculus).

**Histology:** Pseudostratified columnar epithelium with stereocilia, thick three-layered smooth muscle wall (inner longitudinal, middle circular, outer longitudinal), which produces strong peristalsis.

**Embryology:** Derived from the mesonephric (Wolffian) duct under testosterone influence (along with the epididymis, seminal vesicles, and ejaculatory duct). Congenital bilateral absence of the vas deferens (CBAVD) is associated with CFTR mutations (cystic fibrosis) -> obstructive azoospermia with normal spermatogenesis. Müllerian-inhibiting substance causes the paramesonephric duct to regress; absent testosterone leads to Wolffian regression.

**Blood supply/innervation:** Artery to the ductus deferens (from the inferior vesical artery, a branch of the anterior division of the internal iliac). Sympathetic innervation (hypogastric nerve, T10-L2) mediates emission (contraction of the ductus deferens, seminal vesicles, prostate). Parasympathetic S2-S4 mediates erection (point), and somatic pudendal nerve mediates ejaculation (bulbospongiosus contraction). Mnemonic: "Point (parasympathetic), Shoot (sympathetic emission), Squirt (somatic pudendal)."

**Clinical significance:** - **Vasectomy:** Bilateral ligation/resection of the ductus deferens through the scrotum; sperm are absent in the ejaculate but volume is essentially unchanged because most semen comes from the seminal vesicles (~60-70%) and prostate. Testosterone levels, libido, and erection are unaffected. Confirm with post-vasectomy semen analysis (azoospermia). Possible complications: sperm granuloma, post-vasectomy pain syndrome, anti-sperm antibodies, rarely recanalization. - **Inguinal hernia repair:** Ductus deferens can be injured; it's an important structure in the spermatic cord, and indirect inguinal hernias travel within the cord (internal spermatic fascia). - **CBAVD:** Obstructive azoospermia with low semen volume, acidic pH, and low fructose (if seminal vesicles are also absent/hypoplastic); normal FSH and testes size. Evaluate for CFTR mutation in both partners. - **Infection:** Epididymitis/funiculitis can involve the ductus deferens (Chlamydia/Gonorrhea in age <35; E. coli in age >35). - **Spermatic cord contents:** Ductus deferens, testicular artery, pampiniform plexus, cremasteric artery, artery of the ductus deferens, genital branch of the genitofemoral nerve, lymphatics, and the remnant of the processus vaginalis. Coverings: external spermatic fascia (external oblique), cremaster muscle/fascia (internal oblique), internal spermatic fascia (transversalis fascia).

**High-yield pearls:** Term "vas deferens" is synonymous. Passes over the ureter near the bladder (risk during pelvic surgery). Sperm are stored mainly in the epididymis tail and ampulla. Sperm pathway mnemonic: SEVEN UP (Seminiferous tubules, Epididymis, Vas deferens, Ejaculatory duct, (Nothing), Urethra, Penis).