The male urethra is a muscular tube (18-22 cm long) that conveys urine from the internal urethral orifice of the urinary bladder to the external urethral orifice, located at the tip of the glans penis in males. The urethra also provides an exit for semen (sperms and glandular secretions). For descriptive purposes, the urethra is divided into four parts.
The intramural (preprostatic) part of the urethra varies in diameter and length, depending on whether the bladder is filling (bladder neck is tonically contracted so the internal urethral orifice is small and high; the filling internal urethral orifice) or emptying (the neck is relaxed so the orifice is wide and low; the emptying internal urethral orifice). The most prominent feature of the prostatic urethra is the urethral crest, a median ridge between bilateral grooves, the prostatic sinuses. The secretory prostatic ducts open into the prostatic sinuses. The seminal colliculus is a rounded eminence in the middle of the urethral crest with a slit-like orifice that opens into a small cul-de-sac, the prostatic utricle. The utricle is the vestigial remnant of the embryonic uterovaginal canal, the surrounding walls of which, in the female, constitute the primordium of the uterus and a part of the vagina. The ejaculatory ducts open into the prostatic urethra via minute, slit-like openings located adjacent to and occasionally just within the orifice of the prostatic utricle. Thus urinary and reproductive tracts merge at this point.
The proximal male urethra (intramural and prostatic parts of the urethra) are supplied by prostatic branches of the inferior vesical and middle rectal arteries.
The veins from the proximal two parts of the urethra drain into the prostatic venous plexus.
The nerves are derived from the prostatic plexus (mixed sympathetic, parasympathetic, and visceral afferent fibers). The prostatic plexus is one of the pelvic plexuses (an inferior extension of the vesical plexus) arising as organ-specific extensions of the inferior hypogastric plexus.