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Development of urethra

The development of male and female urethra is different .

The female urethra is short and its development is very simple but male urethra is long and its development is complicated

The development of male urethra is intimately related to the development of external genital organs

The epithelium of entire female urethra and most of the male urethra is derived from urogenital sinus

Uregenital sinus is developed from cloaca

What is cloaca ?

Cloaca : part of hindgut (derived from endoderm) caudal to attachment of allantois, which is common chamber for hindgut & urinary system

It is divided into two parts ventral and dorsal by urorectal septum
ventral part is called primitive urogenital sinus
dorsal part is called primitive rectum

What are the parts of primitive urogenital sinus ? 

Vesico-urethral canal and definitive urogenital sinus 

From above down ward different parts of primitive urogenital sinus 

1.      Upper part of vesico-urethral canal

2.      Lower part of vesico-urethral canal

3.      Pelvic part of definitive urogenital sinus

4.      Phallic part of definitive urogenital sinus 

Development of female urethra 

Parts of primitive urogenital sinus	Female urethra
1.      Lower part of vesico-urethral canal	Most of the part of female urethra (upper part)
2.      Pelvic part of definitive urogenital sinus	Small part of female urethra (lower part)
3.      Phallic part of definitive urogenital sinus	Vestibule of female external genitalia into which the urethra is opened  (external opening )

SN: only the lining epithelium of the urethra is derived from endoderm of urogenital sinus

Connective tissue and smooth muscles of urethra are derived from surrounding splanchnopleuric layer of lateral plate mesoderm (intraembryonic mesoderm ) 

Development of male urethra

Parts of primitive urogenital sinus	Male  urethra
1.      Lower part of vesico-urethral canal	Prostatic part of urethra up to the level of opening of ejaculatory duct
2.      Pelvic part of definitive urogenital sinus	Prostatic part of urethra below the opening of ejaculatory duct and membranous part of urethra
3.      Phallic part of definitive urogenital sinus	Penile part of urethra
4.      Surface ectoderm	Terminal part (which occupies the glans penis )

SN: most of the lining epithelium of the male urethra is derived from endoderm of urogenital sinus but the epithelium of terminal part of male urethra is derived from surface ectoderm  

Connective tissue and smooth muscles of urethra are derived from surrounding splanchnopleuric layer of lateral plate mesoderm (intraembryonic mesoderm ) 

Difference between male and female development of urethra

Parts of primitive urogenital sinus	Male  urethra	Female urethra
1.      Lower part of vesico-urethral canal	Prostatic part of urethra up to the level of opening of ejaculatory duct	Most of the part of female urethra (upper part)
2.      Pelvic part of definitive urogenital sinus	Prostatic part of urethra below the opening of ejaculatory duct and membranous part of urethra	Small part of female urethra (lower part)
3.      Phallic part of definitive urogenital sinus	Penile part of urethra	Vestibule of female external genitalia into which the urethra is opened  (external opening )
4.      Surface ectoderm	Terminal part (which occupies the glans penis )	×