Friday, March 20, 2015

Urethral anatomy

Posted by Radiology Madeeasy

Urethral anatomy

A 28 year old man requires a urethral catheter to be inserted prior to undergoing a splenectomy. Where is the first site of resistance to be encountered on inserting the catheter?

  

A.

Bulbar urethra

 

 

B.

Membranous urethra

  

C.

Internal sphincter

 

 

D.

Prostatic urethra

  

E.

Bladder neck


 

The membranous urethra is the least distensible portion of the urethra. This is due to the fact that it is surrounded by the external sphincter.

 

Urethral anatomy

Female urethra


The female urethra is shorter and more acutely angulated than the male urethra. It is an extra-peritoneal structure and embedded in the endopelvic fascia. The neck of the bladder is subjected to transmitted intra-abdominal pressure and therefore deficiency in this area may result in stress urinary incontinence. Between the layers of the urogenital diaphragm the female urethra is surrounded by the external urethral sphincter, this is innervated by the pudendal nerve. It ultimately lies anterior to the vaginal orifice.

Male urethra


In males the urethra is much longer and is divided into four parts.

Pre-prostatic urethra

Extremely short and lies between the bladder and prostate gland.It has a stellate lumen and is between 1 and 1.5cm long.Innervated by sympathetic noradrenergic fibres, as this region is composed of striated muscles bundles they may contract and prevent retrograde ejaculation.

Prostatic urethra

This segment is wider than the membranous urethra and contains several openings for the transmission of semen (at the midpoint of the urethral crest).

Membranous urethra

Narrowest part of the urethra and surrounded by external sphincter. It traverses the perineal membrane 2.5cm postero-inferior to the symphysis pubis.

Penile urethra

Travels through the corpus songiosum on the underside of the penis. It is the longest urethral segment.It is dilated at its origin as the infrabulbar fossa and again in the gland penis as the navicular fossa. The bulbo-urethral glands open into the spongiose section of the urethra 2.5cm below the perineal membrane.

The urothelium is transitional in nature near to the bladder and becomes squamous more distally.