Histology Fact Sheet: Urethra

Histology of the Urethra

Urine leaves the bladder through a tube-like structure called the urethra. The lining of the urethra is epithelium. The wall of the urethra is smooth muscle.

Urine flow is controlled by two uretheral sphincters: the internal urethral sphincter and the external urethral sphincter.  The internal urethral sphincter is at the start of the urethra.  This sphincter is composed of smooth muscle.  The external urethral sphincter is skeletal muscle.

Histology of the Female Urethra

The urethra in females is short.  It is only about about 1.5 inches lengthwise. The lining epithelium of the female urethra is psuedostratified columnar epithelium and stratified sqauamous epithelium.

Histology of Male Urethra

The urethra in the male is longer than the urethra of females.  The male urethra is 7 to 8 inches lengthwise.  The male urethra fuctions as a conduit for urine and semen. The male urethra is divided into three sections: prostatic urethra, membranous urethra, and spongy (penile) urethra. 

Histology of the Prostatic Urethra

The first portion of the male urethra is the prostatic urethra.  This portion of the urethra goes through the prostate gland.  The prostatic urethra is lined by transitional epithelium.

Histology of the Membranous Urethra

The second part of the male urethra is the membranous urethra.  This is a short segment.  The lining epithelium of the membranous urethra is psuedostratified columnar epithelium.

Histology of the Spongy Urethra

The third part of the urethra is the spongy urethra.  The spongy urethra is also called the penile urethra.  This is the longest section of the male urethra.  It travels through the corpus spongiosum of the penis.  The lining epithelium of the spongy urethra is psuedostratified columnar epithelium which then transitions to stratified squamous epithelium distally.

Sources:

Histology: A Text and Atlas
Michael H. Ross/Edward J. Reith

http://www.training.seer.cancer.gov; funded by the U.S. National Cancer Institute's Surveillance, Epidemiology and End Results (SEER) Program, via contract number N01-CN-67006, with Emory University, Atlanta SEER Cancer Registry, Atlanta, Georgia, U.S.A.