Development Of Urinary Bladder &Urethra
 Dr. Nimir
 Dr. Safaa
 Objectives:
 Describe the development of the cloaca and
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urogenital sinus.
Discuss parts of the urogenital sinus.
Understand the origin of different parts of the
bladder.
Congenital anomalies of the bladder.
Understand the origin of different parts of the
urethra.
Congenital anomalies of the urethra.
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The lower urinary system composed of the:
Bladder and the urethra .
Is formed from the endoderm of the hindgut.
During the fourth to seventh weeks of development, the
Cloaca divides into the urogenital sinus anteriorly and the
anal canal posteriorly .
Three portions of the urogenital sinus can be distinguished:
1. The upper largest part(vesical) gives the urinary bladder.
2. The pelvic part in male gives rise to the prostatic and
membranous parts of the urethra, in female it gives the
whole urethra and part of the vagina.
3. The phallic part differs between male & female.
 The bladder develops
mainly from the vesical
part of the urogenital
sinus, but its trigone
region is derived from
the caudal ends of the
mesonephric ducts.
 The entire epithelium of
the bladder is derived
from the endoderm of
the vesical part.
 The other layers of its
wall develop from
adjacent splanchnic
mesenchyme.
 Initially, the bladder
is continuous with the
allantois.
 The allantois
obliterates and form a
thick fibrous cord, the
Urachus.
 The urachus connects
the apex of the
bladder with the
umbilicus.
 In the adult, it is
known as the median
umbilical ligament.
 The caudal portions of the mesonephric ducts are absorbed
into the wall of the urinary bladder .
 The distal parts of the mesonephric ducts in the male
become the ejaculatory ducts.
 The mucosa of the bladder formed by incorporation of the
ducts (the trigone of the bladder) is mesodermal.
 With time is replaced by endodermal epithelium.
 Development of the urethra :
The urethra forms itself from the lower part of the urogenital sinus (UGS).
 In a male the prostate and membranous part of the urethra arise from the
pelvic part of the UGS while the spongy urethra comes from the phallic part
(urethral plate).
 In female the whole urethra and part of the vagina arise from the pelvic part of
the UGS while the phallic part (urethral plate) forms the vestibule and the labia
minora.
 The connective tissue and smooth muscle of the urethra in both sexes are
derived from splanchnic mesenchyme.
Development of the urethra in female
The female urethra develops
from
the
pelvic
urogenital sinus
part
of
 The epithelium of the
urethra in both sexes is
endoderm.
 The epithelium of the
prostatic urethra forms
the prostate gland in
male.
 In the female, the cranial
part of the urethra gives
rise to the urethral and
para-urethral glands.
 Bladder Defects:
Urachal fistula=Persistance of intraembryonic portion of
the allantois ( urine drains through umblicus).
Urachal cyst= Persistance of local area of allantois.
Urachal sinus= Persistance of the upper part of allantois.
 Exstrophy of the bladder is a ventral body wall defect in
which the bladder mucosa is exposed (occurs
2/100,000).
 Epispadias is a constant feature .
 Exstrophy of the bladder is due to lack of mesodermal
migration between the umbilicus and genital tubercle.
 Exstrophy of the cloaca is
a severe ventral body wall
defect in which migration
of mesoderm to the
midline is inhibited.
 The defect includes
exstrophy of the bladder,
spinal defects
,imperforate anus, and
usually omphalocele.