Urinary System Embryology Questions

The lower ends of the mesonephric
ducts are incorporated into the posterior
wall of the urinary bladder. The mesonephric ducts contribute to the connective
tissue component of the posterior wall at
the trigone. It is generally believed that the
transitional epithelium lining the entire
bladder (even the trigone) is of endodermal origin.

The transitional epithelium lining the
ureter is derived from mesoderm because
the ureter develops from the ureteric
bud. The ureteric bud is a diverticulum
from the mesonephric duct whose origin
can be traced back to the intermediate
mesoderm.

The moist, red tissue mass that is
exposed to the exterior is actually the
posterior wall of the urinary bladder. This
is called exstrophy of the bladder and is
caused when the anterior abdominal wall
and anterior wall of the bladder fail to
form. The ureters open onto the posterior
wall; therefore, urine drainage is apparent.

The upper end of the urogenital sinus
is in patent communication with the allantois, which lies in the umbilical cord. The
allantois normally regresses and forms a
fibrous cord. If a remnant persists, it forms
a urachal cyst or sinus.

The metanephros begins to form at
week 5 and starts to function in the fetus
at about week 10. The pronephros is not
functional in humans. The mesonephros is
the interim kidney, which functions until
the metanephros is ready.The metanephros begins to form at
week 5 and starts to function in the fetus
at about week 10. The pronephros is not
functional in humans. The mesonephros is
the interim kidney, which functions until
the metanephros is ready.

The distal convoluted tubule, loop of
Henle, proximal convoluted tubule, and
Bowman capsule are all derived from the
metanephric vesicle.

The podocytes of Bowman capsule
develop from the metanephric vesicles,
which are of mesodermal origin.

The transitional epithelium lining the
urinary bladder is derived from endoderm
because the urinary bladder develops from
the upper end of the urogenital sinus. The
origin of the urogenital sinus can be traced
back to the gut tube, which is lined by
endoderm.

A urachal cyst or sinus forms from a
remnant of the allantois and is found along
the midline on a path from the umbilicus
to the apex of the urinary bladder. The
epithelium lining the cyst produces secretions that gradually fill the remnant with
fluid. Very rarely, the entire allantois persists, forming a fistula that is patent from
the urinary bladder to the exterior at the
umbilicus

The ureteric bud seems to be preprogrammed to undergo repeated divisions.
These divisions normally begin on contact
with the metanephric blastema. If the ureteric bud undergoes division prematurely,
duplication of the ureter and renal pelvis
occurs. In some circumstances, two separate kidneys may form.