Transcript Urogenital System

Urogenital System Development
Quick review
Embryo folding
• The urogenital system
develops from the
intermediate mesenchyme
inthe dorsal wall of the
embryo
• A longitudinal elevation of
the mesenchyme—the
urogenital ridge—forms on
each side of the dorsal
aorta
• The part of the urogenital
ridge that gives rise to the
urinary system is the
nephrogenic cord (lateral)
• the part that gives rise to
the genital system is the
gonadal ridge (medial)
DEVELOPMENT OF URINARY SYSTEM
•
The urinary system develop
before the genital system(4th
week)
•
Three sets of kidneys, develop in
human embryos.
•
The first set—the pronephroi—is
rudimentary and never functions.
•
The second set—the
mesonephroi—is well developed
and functions for a brief period.
•
The third set—the metanephroi—
becomes the permanent kidneys.
Pronephroi
• appear early in the
fourth week of
development.
• The pronephric ducts
run caudally and open
into the cloaca
• The pronephroi
degenerate but most
of the pronephric
ducts persist and are
used by the next set of
kidneys.
Mesonephroi
• appear late in the fourth week
caudal to the pronephroi
• function as interim kidneys until
the permanent kidneys develop
• The mesonephroi consist of
glomeruli and mesonephric
tubules
• The tubules open into the
mesonephric ducts, originally the
pronephric ducts.
• The meso-nephroi
degenerate toward
the end of the first
trimester;
• however, their
tubules become the
efferent ductules of
the testes,
• the mesonephric
ducts have several
adult derivatives in
the male
Metanephroi
• begin to develop early in the
fifth week and start to
function approximately 4
weeks later.
• The urine is excreted into the
amniotic cavity.
• The permanent kidneys
develop from two sources of
mesodermal origin:
• The ureteric bud
• The metanephric blastema
• The ureteric bud is an
outgrowth from the
mesonephric duct, near
the cloaca, and is the
primordium of the ureter,
renal pelvis, calices, and
collecting tubules
• The elongating bud
penetrates the
metanephrogenic
blastema—a mass of
cells derived from the
nephrogenic cord—that
forms the nephrons
• The stalk of the ureteric
bud becomes the
ureter,
• undergoes repetitive
branching to form the
collecting
tubules,major calices
minor calices.
• The end of each arched
collecting tubule
induces clusters of
mesenchymal cells in
the metanephrogenic
blastema to form small
metanephric vesicles
• These vesicles
elongate and become
the renal tubules
• Each distal convoluted
tubule contacts an
arched collecting
tubule.
• The tubules become
confluent, forming a
uriniferous tubule.
• The fetal kidneys are subdivided into lobes. The
lobulation usually disappears during infancy as
the nephrons increase and grow.
• At term, nephron formation is complete—each
kidney containing approximately 1.5 million
nephrons.
• Functional maturation of the kidneys occurs
after birth
Positional Changes of Kidneys
• The metanephric kidneys lie close
to each other in the pelvis
• The caudal part of the embryo
grows away from the kidneys so
that the kidneys occupy
progressively higher cranial levels.
• As the kidneys change their
positions “ascend,” they rotate
medially almost 90 degrees. By
the ninth week, the kidneys come
in contact with the suprarenal
glands as they attain their adult
position
Changes in Blood Supply of Kidneys
•
Initially, the renal arteries are
branches of the common iliac
arteries
•
Later, the kidneys receive their
blood supply from the distal
end of the aorta
•
The kidneys receive their most
cranial arterial branches from
the abdominal aorta which
become the renal arteries.
•
Normally, the caudal primordial
branches undergo involution
and disappear.
Unilateral renal agenesis
• Boys are affected
more often than girls
• left kidney is usually
the one that is absent
• other kidney usually
undergoes
compensatory
hypertrophy
Bilateral renal
agenesis
• incompatible with postnatal life
• Failure of the Uretric budto penetrate the
metanephrogenic blastema
Ectopic Kidneys
• Most ectopic kidneys are
located in the pelvis, but
some lie in the inferior
part of the abdomen.
• Pelvic kidneys and other
forms of ectopia result
from failure of the
kidneys to “ascend.”
MALROTATION OF THE KIDNEYS
• If the kidney does not
rotate, the hilum faces
anteriorly (embryonic
position)
• If the hilum faces
posteriorly, then
rotation has
progressed too far; if
it faces laterally, then
medial rotation has
occurred.
DUPLICATIONS OF THE URINARY
TRACT
• These anomalies result from division of the metanephric
diverticulum.
• Incomplete division of the ureteric primordium results in a
divided kidney with a bifid ureter
• Complete division results in a double kidney with a bifid
ureter or with separate ureters
• A supernumerary kidney with its own ureter probably
results from the formation of two metanephric diverticula.
Crossed fused renal ectopia
• The developing
kidneys fuse while
they are in the pelvis,
• and one kidney
“ascends” to its
normal position,
carrying the other one
with it.
Discoid kidney(Lump Kidney) resulting
from fusion of the kidneys while they
were in the pelvis.
Horseshoe Kidney
• the poles of the kidneys
are fused (usually the
inferior poles)
• Normal ascent of the
fused kidneys is
prevented because they
are caught by the root of
the inferior mesenteric
artery.
PELVI-URETERIC JUNCTION (PUJ)
OBSTRUCTION
• congenital PUJ
obstruction but may be as
a result of:
• abnormal merging of the
ureter into the renal
pelvis,
• abnormal arrangement of
ureteric musculature at
the PUJ
• crossing vessel (usually
artery) running in front of
the PUJ causing an
obstruction.
• The classic symptoms of a PUJ obstruction are:
• Flank pain – often worsened after consuming
large volumes of fluids, especially alcohol
• Recurrent urinary tract infections
• Blood in urine (haematuria)
• Rx: Pyeloplasty
Vesicoureteral reflux
• Insufficient
sub mucosal
tunneling and
valve
development
as the ureter is
incorporated
into the
urinary
bladder.
Development of Urinary Bladder
•
Division of the cloaca by the urorectal
septum into a dorsal rectum and a
ventral urogenital sinus
•
the urogenital sinus is divided into three
parts:
•
A cranial vesical part that forms most of
the bladder and is continuous with the
allantois
•
A middle pelvic part that becomes the
urethra in the neck of the bladder, the
prostatic part of the urethra in males,
and the entire urethra in females
•
A caudal phallic part that grows toward
the genital tubercle—the primordium of
the penis or the clitoris
• Initially, the bladder is
continuous with the allantois
• The allantois soon constricts
and becomes a thick, fibrous
cord, the urachus
• In adults, the urachus is
represented by the median
umbilical ligament.
• Urachal cysts:
• The most
common site
for these cysts
is in the
superior end of
the urachus,
just inferior to
the umbilicus.
• Two types of
urachal sinuses :
• one that opens
into the bladder
and one that
opens at the
umbilicus.
• Patent
urachus or
urachal
fistula.
• distal parts of the mesonephric
ducts are incorporated into its dorsal
wall and contribute to the formation
of the connective tissue in the
trigone of the bladder.
• The epithelium of the entire
bladder is derived from the
endoderm of the urogenital sinus.
• As the mesonephric ducts are
absorbed, the ureters come to open
separately into the urinary bladder
• In males, the orifices of the
mesonephric ducts move close
together and enter the prostatic part
of the urethra as the caudal ends of
these ducts become the ejaculatory
ducts.
• In females, the distal ends of the
mesonephric ducts degenerate
Development of Urethra
• The epithelium of
most of the male
urethra and the
entire female
urethra is derived
from the endoderm
of the urogenital
sinus
• The distal part of
the urethra in the
glans of the penis is
derived from a solid
cord of ectodermal
cells
Hypospadias
• Hypospadias is the most
common anomaly involving the
penis and is found in 1 in 300
male infants.
• In glanular hypospadias, the
external urethral orifice is on
the ventral surface of the glans
penis
• Hypospadias results from
inadequate production of
androgens by the fetal testes,
inadequate receptor sites for
these hormones, or both.
DEVELOPMENT OF THE
REPRODUCTIVE SYSTEMS
• The gonads arise from intermediate
mesoderm within the urogenital
ridges of the embryo
• The genital ducts arise from paired
mesonephric and paramesonephric
ducts
• The mesonephric ducts give rise to
MALE genital ducts
• The paramesonephric ducts give rise
to FEMALE genital ducts
DEVELOPMENT OF GONADS
•
The early genital systems in the two sexes are similar;
therefore, the initial period of genital development is
referred to as the indifferent state of sexual
development
•
Gonadal development begins during the fifth week
•
Before the seventh week, the gonads of the two sexes
are identical in appearance and are called indifferent
gonads
•
The gonads (testes and ovaries) are derived from
three sources:
Mesothelium (mesodermal epithelium) lining the
pos-terior abdominal wall
•
•
Underlying mesenchyme
•
Primordial germ cells: originate in the wall of the
umbilical vesicle and migrate along the dorsal
mesentery of the gut to the gonadal ridges (from the
4th to 6th week)
Development of Testes
• A coordinated sequence of genes induces the
development of testes.
• The SRY gene for the testis-determining factor
(TDF) on the short arm of the Y chromosome
acts as the switch that directs the
development of the indifferent gonad into a
testis.
• . The connection of the
prominent gonadal
cords—the seminiferous cords—with the
surface epithelium is lost
when the tunica
albuginea develops.
• The seminiferous cords
develop into the
seminiferous tubules,
the straight tubules
(tubuli recti), and the
rete testis.
•
The seminiferous tubulesare separated by the mesen-chyme, giving rise to the
interstitial cells(of Leydig). By the eighth week, these cells secrete androgenic
hormones— testosteroneand androstenedione—that induce mascu-line
differentiation of the mesonephric ducts and the external genitalia.
•
The seminiferous tubules remain solid (i.e., without lumina) until puberty, when
lumina begin to develop.
•
The fetal testes also produce a glycoprotein known as müllerian-inhibiting
substance (MIS) or antimüllerian hormone. MIS is produced by the sustentacular
(Sertoli) cells, which are present until puberty, at which time the levels of MIS
decrease.
•
MIS suppresses the development of the paramesonephric ducts, which form the
uterus and uterine tubes. The semi-niferous tubules remain until puberty (i.e.,
without lumina), when lumina begin to develop.
• The rete
testisbecomes
continuous with 15 to
20 mesonephric
tubules that become
efferent ductules.
• These ductules are
connected with the
mesonephric duct,
which becomes the
ductus epididymis
Descent of the testes
• The testes arise in the lumbar
region but then descend into
pelvic cavity and through the
inguinal canal to end up in the
scrotum
• Descent of the testis is due to
tethering of the testes to the
anterior body wall by the
gubernaculum.
• With growth and elongation of
the embryo coupled with
shortening of the
gubernaculum, the testes are
pulled through the body wall,
then the inguinal canal, and
finally into the scrotum.
Development of Ovaries
•
Gonadal cordsextend into the
medulla of the ovary and
form a rudimentary rete ovarii
that degenrates shortly
•
As the secondry cortical cords
increase in size, primordial
germ cellsare incorporated
into them.
•
At approximately 16 weeks,
these cortical cords begin to
break up into isolated cell
clusters—primordial
follicles—each of which
consists of an
oogonium(derived from a
primordial germ cell), surrounded by a single layer of
follicular cells derived from
the surface epithelium
Development of Male Genital Ducts
• These ductules open into the
mesonephric duct, which has
been transformed into the duct
of the epididymisin this region.
• Distal to the epididymis, the
mesonephric duct acquires a
thick investment of smooth
muscle and becomes the
ductus deferens.
• The Distal part of the
mesonephric duct becomes the
ejaculatory duct.
• Seminal Gland A lateral
outgrowth from the caudal
end of each mesonephric duct
gives rise to the seminal
gland(vesicle). The secretions
of this pair of glands nourish
the sperms
• Prostate Multiple endodermal
outgrowths arise from the
prostatic part of the urethra
and grow into the surrounding mesenchyme
Development of Female Genital
Ducts and Glands
• The uterine tubesdevelop
from the unfused cranial
parts of the
paramesonephric ducts
• The caudal, fused portions
of these ducts form the
uterovaginal primordium,
which gives rise to the
uterus and the superior
portion of the vagina
•
The vaginal epithelium is derived
from the endoderm of the
urogenital sinus. The fibromuscular
wall of the vagina develops from the
surrounding mesenchyme.
•
Formation of a vaginal plate
•
The central cells of this plate break
down, forming the lumen of the
vagina. The peripheral cells of the
plate form the vaginal epithelium or
lining
•
Outgrowths from the urogenital
sinus form bilateral greater
vestibular glands(of Bartholin) in
the lower one third of the labia
majora.
Double Uterus
• A double uterus (uterus
didelphys) results from
failure of fusion of the
inferior parts of the
paramesonephric ducts
• It may be associated with a
double or a single vagina
• In many of these cases, the
indi viduals are fertile, but
may have an increased
incidence of premature
delivery.
Summary of male urogenital tract
derivatives
• Ureteric bud: ureter
• Mesonephric ducts: rete testis, efferent ducts,
epididymis, vas deferens, seminal vesicle,
trigone of bladder
• Urogenital sinus: bladder (except trigone),
prostate gland, bulbourethral gland, urethra
Summary of female urogenital tract
derivatives
• Ureteric bud: ureter
• Mesonephric ducts: trigone of bladder
• Paramesonephric ducts: oviduct, uterus, upper
1/3 of vagina
• Urogenital sinus: bladder (except trigone),
vestibular gland, urethra, lower 2/3 of vagina