The male urethra connects the bladder to the outside of the body, and is typically considered in four parts.
Pre-prostatic urethra
The pre-prostatic urethra is the short part between the bladder and the prostate.
Prostatic urethra
The prostatic urethra is that part within the prostate gland, and is (normally) the broadest part. It is remarkable for its posterior aspect, which contains the urethral crest. The prostatic utricle, a blind ending process, passes inferiorly and superiorly from the central part of the crest and is an important landmark. The two ejaculatory ducts open into the crest, just inferior and lateral to the utricle.
Membranous urethra
This short segment extends from the apex of the bladder until the urethra enters the bulb of the penis. The deep transverse perineal muscle and sphincter urethrae (previously thought to be part of the 'urogenital diaphragm') form a sphincter at this level.
Spongy urethra
The urethra makes a 90o turn in the penile bulb and then passes anteriorly, in the ventral part of the corpus spongiosum. It terminates in the glans of the penis at the external urethral orifice.
Microscopic Structure
The urethra is initally lined with transitional epithelium. This gives way to stratified squamous epithelium within the spongy urethra.
