Ureters are a component of the urinary system and are thin tubes of muscle that carry urine from the kidneys to the bladder. In a human adult, the ureters are usually 8–12 in long and very small in diameter (~0.15 in).
Though they sound similar, ureters are different from the urethra in that ureters connect the kidneys to the bladder whereas the urethra connects the bladder to the outside body.
Sperm is forcefully expelled from the tail of the epididymis into the deferent duct during ejaculation. Sperm then travels through the deferent duct into the pelvic cavity, over the ureter to the prostate behind the bladder. Here, the vas deferens joins with the seminal vesicle to form the ejaculatory duct, which passes through the prostate and empties into the urethra. When ejaculation occurs, muscle movements propel the sperm forward.
The ureters have been identified for at least two thousand years, with the word “ureter” stemming from the stem uro- relating to urinating and seen in written records since at least the time of Hippocrates.