Embryology: Lecture 2: Development and Anomalies of Urinary Tract

EMBRYOLOGY
Lecture 2 : Development and anomalies of urinary tract

In Brief ….
- Urethra
Cloaca • Develop.
• Anomalies
- Urinary
bladder
Clinical
• Develop.
Correlate
•
Anomalies.
I
Cloaca
● Definition: Is the
expanded caudal
and terminal part
of the hindgut
(caudal to the
origin of the
allantois).
● Origin :
Endodermal lined
cavity
Boundaries
Before Folding-:
☆Caudal : Cloacal membrane which lies in

contact with surface ectoderm.
☆Cranial: continuous with hindgut.
☆Ventral: receive the allantois.
☆Lateral : mesonephric ducts.
After Folding-:
☆The cloacal membrane becomes ventral.

Boundaries
Before Folding-:
☆Caudal : Cloacal membrane which lies in

contact with surface ectoderm.
☆Cranial: continuous with hindgut.
☆Ventral: receive the allantois.
☆Lateral : mesonephric ducts.
After Folding-:
☆The cloacal membrane becomes ventral.

Division of the cloaca
❑ The urorectal septuma )lamredosem(rises in the angle
between allantois & hindgut.
❑ This septum grows caudally dividing the cloaca into:
▪An anterior part called the primitive urogenital sinus

forming the UB and urethra.
▪ A posterior part called the recto-anal canal forming

the rectum and anal.
❑ It also divides the cloacal membrane into:
▪ A urogenital (urethral(membrane (in front).
▪ An anal membrane (behind).
❑The tip of the urorectal septum will form the perineal

body
Subdivision of the
primitive urogenital
sinus
- The primitive urogenital sinus
is subdivided by the point of
entrance of the mesonephric
duct into:
• Vesico-urethral canal,the
upper part.
• Definitive urogenital
sinus,the lower part.
• Its upper segment is called
the pelvic part.
• Its lower segment is called
the phallic part.
Fate of vesicourethral canal & definitive
urogenital sinus:
• Vesicourethral canal: :
• upper part gives rise to
Urinary bladder except trigone.
• lower part gives Upper ½ of
anterior of prostatic urethra (in
♂), the whole anterior wall of
urethra (in ♀).
• Definitive urogenital sinus:
gives rise to
• The pelvic part of the

urogenital sinus gives rise to
lower ½ of prostatic and
membranous urethra (in ♂).
And lower part of vagina in
female.
• The phallic part of
the urogenital sinus:
• It is flattened from
side to side, and as
the genital tubercle
grows, this part of
the sinus will be
pulled ventrally. • It
gives rise to most of
the spongy urethra
(in ♂) & vestibule of
vagina (in ♀).
• The phallic part of
the urogenital sinus:
• It is flattened from
side to side, and as
the genital tubercle
grows, this part of
the sinus will be
pulled ventrally. • It
gives rise to most of
the spongy urethra
(in ♂) & vestibule of
vagina (in ♀).
II
- Urinary bladder :- • Develop. • Anomalies
sources
1- Vesicourethral canal: upper
part forms the urinary bladder
except the trigone.
2- Allantois:
❑ Its proximal part is

incorporated into the bladder as
the apex.
❑ Its distal part becomes fibrosed

to form urachus. In the adult the
urachus is represented by the
median umbilical ligament.
3- Lower or distal parts of the 2
mesonephric ducts:
form the CT in the trigone of UB.
• Early they open into the vesicourethral

canal.
• Then the distal portions of the

mesonephric ducts and attached ureteric
ducts become incorporated into the
posterior wall of the bladder.
• So the 2 mesonephric ducts & 2 ureters

open separately into the urinary
bladder.
• The mseodermal tissue of trigone is

later overgrown by endoderm from the
SBW
Congenital anomalies of
the bladder:
1) Persistence of a patent urachus

: • Urachal fistula: persistence of
the whole urachus patent. Urine
may dribble from the umbilical.
• Urachal cyst: persistence of an
isolated segment of the urachus
patent.
• Urachal sinus: persistence of
the upper part patent.
• Urachal ddiverticulum:-
the lumen of the proximal
part of urachus remains
patent and becomes
continuous with UB and UB
becomes tubular in shape.
2) Ectopia vesicae (Exstrophy of the bladder)
Cause: Absence of the mesoderm in the

region extends from the umbilicus to the
cloacal membrane.
Features:
-High α- fetoprotein in amniotic.
- Absence of the infra-umbilical part of the

anterior abdominal wall & anterior wall of
the urinary bladder.
- Exposure and protrusion of the trigone of

the bladder and the ureteric orifices.
- - Wide separation of the pubic bones.
- - Penis is divided into two parts and

halves of the scrotum widely separated.
- -Epispadius are associated.

III
anomalies •Develop. •Urethra
Female urethra
DEVELOPMENT: Female
urethra:is derived
from:causal part of
Vesico-urethral canal
“Ant. Wall” &absorbed
parts of the mesonephric
ducts”post. wall".
Male urethra
1- Preprostatic & upper part of
prostatic urethra: is derived from:
Vesico-urethral canal “anterior wall” &
absorbed parts of the mesonephric
ducts “posterior wall".
2- Lower part of the prostatic urethra
& membranous urethra: Is derived
from the pelvic part of the definitive
urogenital sinus
3- Spongy ( penile ) urethra: The
endodermal cells lining the lumen of
the phallic part of the definitive
urogenital sinus proliferate to form the
urethral plate.
THE URETHRAL PLATE:
• The phallus pulls the urethral
folds forward so that they form
the lateral walls of the urethral
groove.
• This groove extends along the

caudal/Ventral aspect of the
elongated phallus but does not
reach the most distal part.
• The epithelial lining of the

groove, which originates in the
endoderm, forms the urethral
plate.
THE URETHRAL PLATE:
• The phallus pulls the urethral
folds forward so that they form
the lateral walls of the urethral
groove.
• This groove extends along the

caudal/Ventral aspect of the
elongated phallus but does not
reach the most distal part.
• The epithelial lining of the

groove, which originates in the
endoderm, forms the urethral
plate.
THE URETHRAL CANAL:
• Is formed by the meeting
& fusion of the urethral
folds together.
• Ends blindly anteriorly at
the glans penis.
4- THE TERMINAL
(GLANDULAR) PART:
• Is developed by a cord
of ectodermal cells
grows from the tip of the
glans.
• Finally, this cord
becomes canalized &
communicates with the
urethral canal.
Congenital anomalies
of urethra
Hypospadius:
• The urethra opens on the

under surface of the penis.
• It is due to failure of
fusion of the edges of the
urethral groove.
Types :-
- Glandular
- Penile
- Penoscrotal
- perineal
Epispadius:
• The urethra opens on the dorsum/

cranial aspect of the penis.
•It is due to development of the

genital tubercle in the region of the
urorectal septum instead of
developing in the cranial margin of
the cloacal membrane. Hence, a
portion of the cloacal membrane is
found cranial to the genital tubercle.
When this membrane ruptures, the
outlet comes to lie on the cranial
aspect of the penis.
• May be associated with ectopia

vesica.
Clinical Note
Don’t do circumcision as the skin

fold will be used to repair the
defects
IV
Clinical Correlate
Kareem is 7 days old new
born baby,born in the
hospital.His mother noticed
that some fluid draining from
the umbilicus onto the
skin.She decided to take her
baby for examination.The
specialist started testing the
fluid from theumbilicus and
identified it as urine.
This is a case of urachal fistula,one of
the anomalies related to
development of the urinarybladder.
•Cause of this case isbnon-

obliteration of the allantois.

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EMBRYOLOGY

Lecture 2 : Development and anomalies of urinary tract

☆Caudal : Cloacal membrane which lies in

☆Cranial: continuous with hindgut.

☆Ventral: receive the allantois.

☆Lateral : mesonephric ducts.

☆The cloacal membrane becomes ventral.

☆Caudal : Cloacal membrane which lies in

☆Cranial: continuous with hindgut.

☆Ventral: receive the allantois.

☆Lateral : mesonephric ducts.

☆The cloacal membrane becomes ventral.

❑ This septum grows caudally dividing the cloaca into:

▪An anterior part called the primitive urogenital sinus

▪ A posterior part called the recto-anal canal forming

❑ It also divides the cloacal membrane into:

▪ A urogenital (urethral(membrane (in front).

▪ An anal membrane (behind).

❑The tip of the urorectal septum will form the perineal

• The pelvic part of the

❑ Its proximal part is

❑ Its distal part becomes fibrosed

form the CT in the trigone of UB.

• Early they open into the vesicourethral

• Then the distal portions of the

• So the 2 mesonephric ducts & 2 ureters

• The mseodermal tissue of trigone is

1) Persistence of a patent urachus

Cause: Absence of the mesoderm in the

-High α- fetoprotein in amniotic.

- Absence of the infra-umbilical part of the

- Exposure and protrusion of the trigone of

- - Wide separation of the pubic bones.

- - Penis is divided into two parts and

- -Epispadius are associated.

• This groove extends along the

• The epithelial lining of the

• This groove extends along the

• The epithelial lining of the

• The urethra opens on the

• The urethra opens on the dorsum/

•It is due to development of the

• May be associated with ectopia

Don’t do circumcision as the skin

•Cause of this case isbnon-

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