On each side of the prostate gland (in the male reproductive system) is an ejaculatory duct.
Each ejaculatory duct is about two centimeters in length and is created when the seminal vesicle's duct merges with the vas deferens. At this point, these ducts travel through the prostate and, at its far end, drain into the colliculus seminalis's urethra.
Semen flows through each ejaculatory duct during ejaculation, traveling through the penis to exit the body.
One ejaculatory duct or both can become obstructed in a congenital (from birth) or acquired pathological complication known as ejaculatory duct obstruction. When both ducts are obstructed, patients are likely to experience symptoms such as infertility and azoospermia (low sperm count) or aspermia (absence of sperm). Transurethral resection is a surgical procedure that can be used to open the ducts; its goal is to make regular ejaculation flow possible once again.
Benign prostatic hyperplasia, which refers to an abnormal increase in prostate size, is another condition that can affect the ejaculatory ducts. Although this condition is correctable by surgery, an ejaculatory duct could be damaged in the process, causing retrograde ejaculation.