The male urethra can be divided into,
- Pre-prostatic urethra
- Prostatic urethra
- Membranous urethra
- Penile urethra. (Spongy part of the urethra)
The prostatic part of the urethra is in between the pre-prostatic and membranous part of the urethra. It is embedded inside the prostatic gland. It is 3 -4cm in length. It passes through the substance of the prostate closer to the anterior than the posterior surface of the gland. From the internal urethral sphincter the prostatic urethra runs downwards and backwards. At the level of the middle of the length of the gland it bends and continue downwards and forwards to emerge from the anterior aspect of the apex.
The proximal part of the prostatic urethra is called as pre-prostatic urethra. It is surrounded by cylindrical smooth muscle which is an extension of the circular muscle at the bladder neck. This makes the internal urethral sphincter. It contracts to prevent seminal regurgitation into the bladder during ejaculation.
Histological features of the lumen of the prostatic urethra
Urethral crest is a midline ridge projects into the lumen from the posterior wall throughout most of the length of the prostatic urethra. The shallow depression on either side of the prostatic crest is termed as prostatic sinusprostatic sinus. There is a midline rounded eminence at about the middle length of the prostatic crest which is called as seminal colliculus or verumontanum. The prostatic utricle is a small recess representing the fused ends of the paramesonephric (Mullerian) ducts which opens on to the middle of the verumontanum and the ejaculatory ducts open on the either side of the utricle.