Ductus deferens (vas deferens)
Ductus deferens
Also known as: vas deferens, vas, sperm duct
A thick-walled muscular tube ≈45 cm long that carries sperm from the tail of the epididymis, through the spermatic cord and inguinal canal, over the ureter, to join the seminal vesicle duct as the ejaculatory duct.
Overview
The ductus deferens has a narrow lumen but a very thick wall of three smooth-muscle layers (inner longitudinal, middle circular, outer longitudinal), so it feels like a firm cord when rolled between finger and thumb in the spermatic cord. Its mucosa is pseudostratified columnar epithelium with stereocilia.
Course: it begins at the tail of the epididymis, ascends medial to the epididymis behind the testis, travels in the spermatic cord through the superficial inguinal ring and inguinal canal, and leaves the cord at the deep inguinal ring, hooking around the lateral side of the inferior epigastric artery. It then crosses the external iliac vessels into the pelvis, runs on the lateral pelvic wall beneath the peritoneum, and crosses superior (anterior) to the ureter near the posterolateral angle of the bladder. It passes medially across the back of the bladder, medial to the seminal vesicle, where it enlarges as the ampulla (a reservoir), then narrows and unites with the duct of the seminal vesicle behind the bladder neck to form the ejaculatory duct.
During emission, sympathetic stimulation produces strong peristaltic contractions that move sperm rapidly from the epididymis to the urethra.
- Location
From the tail of the epididymis via the spermatic cord, inguinal canal and lateral pelvic wall to the base of the prostate behind the bladder.
Parts & subdivisions
- Scrotal partAscends behind the testis medial to the epididymis.
- Within the spermatic cord — the site of vasectomy.
- Inguinal partTraverses the inguinal canal.
- Pelvic partCrosses the external iliac vessels and the ureter ("water under the bridge").
- AmpullaDilated terminal part behind the bladder, medial to the seminal vesicle.
Anatomy
- Innervation
Sympathetic fibres from the inferior hypogastric (pelvic) plexus (L1–L2) — α1-adrenergic contraction during emission.
- Arterial supply
Artery to the ductus deferens (usually from the superior vesical, sometimes inferior vesical artery), which accompanies it to the testis and anastomoses with the testicular artery.
- Venous drainage
Vein of the ductus deferens → pampiniform plexus and vesical/prostatic venous plexus.
- Lymphatic drainage
External and internal iliac nodes.
- Relations
In the inguinal canal: lateral to it lies the deep ring; in the pelvis it crosses the external iliac vessels, the obliterated umbilical artery and the ureter, all of which lie deep to it; behind the bladder it lies medial to the seminal vesicle and anterior to the rectum.
- Histology
Small, stellate lumen; pseudostratified columnar epithelium with stereocilia; very thick three-layered smooth muscle coat; adventitia.
- Development
Mesonephric (Wolffian) duct.
Function
- Transports sperm from the epididymis to the ejaculatory duct during emission.
- Stores sperm in the ampulla.
Clinical significance
Vasectomy
Division and ligation of both vasa through small scrotal incisions. Sperm production continues but sperm are resorbed; the ejaculate volume is almost unchanged because >95 % comes from accessory glands. Not immediately effective — sperm persist in the distal tract, so semen analysis confirms azoospermia (usually ≈12 weeks later).
Congenital bilateral absence of the vas deferens (CBAVD)
Found in almost all men with cystic fibrosis and some with milder CFTR mutations: obstructive azoospermia with low-volume, acidic, fructose-negative semen; sperm can be retrieved surgically for ICSI.
Mnemonics
Water under the bridge
The ureter (water) passes under the ductus deferens (bridge) behind the bladder.
Compiled from standard anatomy and physiology references — see the Reproductive System sources. For education only; not medical advice.