Transcript Development of the Urinary System

Development of the Urinary System
Ahmed Abdellatif, MD, PhD
Objectives
Describe the development of the Urinary System, i.e.
• Nephrogenic cord; pronephros, mesonephros, &
metanephros.
• Collecting System; Ureters, Urinary bladder,
Urethera.
• Migration of the kidney & its effect on blood supply
Describe the development of Suprarenal glands; Cortex
& Medulla.
• Congenital Anomalies.
Urogenital ridge
• Urogenital ridge
– From intermediate
mesenchyme
(mesoderm)
– Longitudinal elevation
on each side of aorta
– Nephrogenic cord 
urinary system
– Gonadal ridge  genital
system
Nephrogenic cord
1. Pronephros
– Bilateral,
– Appear early in the 4th
week in the neck region.
– The pronephric ducts run
caudally and open into
the cloaca.
– The pronephroi
degenerate.
– The pronephric ducts
persist and are used by
the next set of kidneys.
Mesonephros
2. Mesonephros.
• Appear late in the 4th week, caudal to
the pronephroi.
• Function as interim kidneys for
approximately 4 weeks, until the
permanent kidneys develop.
• Consist of glomeruli (10-50 per
kidney) and tubules.
• The mesonephric tubules open into
bilateral mesonephric ducts,
originally the pronephric ducts.
• The mesonephric ducts open into
the cloaca.
• Degenerates end of 1st trimester.
Early in 4th week
Late in 4th week
5th week
Table 12-1. Derivatives and Vestigial Remains
of Embryonic Urogenital Structures
MALE
Efferent ductules of
testis
Paradidymis
Appendix of
epididymis
Duct of epididymis
Ductus deferens
Ureter, pelvis, calices,
and collecting tubules
Ejaculatory duct and
seminal gland
EMBRYONIC
STRUCTURE
FEMALE
Mesonephric tubules Epoophoron
Mesonephric duct
Paroophoron
Appendix vesiculosa
Duct of epoophoron
Longitudinal duct;
Gartner duct
Ureter; pelvis,
calices, and
collecting tubules
Metanephros
3. Metanephros
•
Metanephroi = primordia of permanent kidneys
•
•
•
Begin to develop in the 5th week.
Become functional 9th weeks.
Urine formation continues throughout fetal life. It is
excreted into the amniotic cavity and mixes with the
amniotic fluid.
The permanent kidneys develop from two sources
•
The ureteric bud is a diverticulum (outgrowth) from the
mesonephric duct near its entrance into the cloaca.
•
The metanephrogenic blastema is derived from the
caudal part of the nephrogenic cord. As the ureteric
bud elongates, it penetrates the metanephrogenic
blastema-a metanephric mass of mesenchyme.
•
A blastema is a mass of cells capable of growth and
regeneration into organs or body parts.
Metanephros
Development of the
Collecting System
The stalk of the ureteric bud becomes
the ureter.
The cranial part of the bud undergoes
repetitive branching, forming branches which
differentiate into the collecting tubules of
the metanephros.
• 1st four generations of tubules enlarge and
become confluent to form the major
calices,
• 2nd four generations coalesce to form
the minor calices.
Development of the Collecting
System
•
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 metanephric tubules (Fig. 127B and C).
The proximal ends of these tubules are
invaginated by glomeruli.
•
Development of the Collecting
System
•
The tubules differentiate into
– Proximal & Distal convoluted tubules
– nephron loop (Henle loop).
Each distal convoluted tubule contacts an arched
collecting tubule, and the tubules become confluent.
(polycystic kidney??).
A uriniferous tubule consists of 2 embryologically
different parts (Figs. 12-6 and 12-7):
• A nephron derived from the metanephrogenic
blastema.
• A collecting tubule derived from the ureteric bud
Fetal Kidneys
•
•
•
•
At full term, nephron formation is
complete, with each kidney
containing as many as 2 million
nephrons.
Fetal kidneys are subdivided
into lobes.
The lobulation usually disappears
at the end of the first year of
infancy as the nephrons increase
and grow.
Increase in kidney size after birth
results mainly from the elongation
of the proximal convoluted tubules
as well as an increase of interstitial
tissue.
Migration of the kidney
•
•
Initially the primordial permanent kidneys lie close to each other in the pelvis, ventral to
the sacrum. As the abdomen and pelvis grow, the kidneys gradually relocate to the
abdomen and move farther apart. They attain their adult position by the ninth week..
Initially the hilum of each kidney face ventrally; kidneys rotate medially almost 90
degrees. By the ninth week, the hila are directed anteromedially.
Changes in Blood Supply of Kidneys
•
Kidneys receive blood supply from:
–
–
–
•
common iliac arteries
distal end of the aorta.
When they are located at a higher level, they receive new branches from the aorta.
Normally the caudal branches of the renal vessels undergo involution and disappear.
Changes in Blood Supply of
Kidneys
ACCESSORY RENAL ARTERIES
• Approximately 25% of adult
kidneys have two to four renal
arteries. Accessory
(supernumerary) renal
arteries usually arise from the
aorta superior or inferior to the
main renal artery and follow it to
the hilum of the kidney (Fig. 1211A, C, and D). Accessory
arteries may also enter the
kidneys directly, usually into the
superior or inferior poles.
Congenital Anomalies of
Kidneys
• Renal Agenesis, unilateral or
bilateral.
• Malrotated Kidney, hilum stays
posterior.
• Horseshoe Kidney.
• Supernumerary kidney, additional
kidneys.
• Ectopic Ureter, opens in an abnormal
area.
Congenital Anomalies
of Kidneys
• Duplications
of Ureter
and/or renal
pelvis.
Congenital Anomalies
of Kidneys
• Ectopic Kidneys,
Most ectopic kidneys
are located in the
pelvis, pelvic
kidneys.
Congenital Anomalies of
Kidneys
•
Cystic Kidney Diseases
–
autosomal recessive polycystic kidney disease,
diagnosed at birth or in utero by ultrasonography,
both kidneys contain many small cysts (Fig. 1219A), which result in renal insufficiency. Death of
the infant usually occurs shortly after birth.
–
Multicystic dysplastic kidney disease results
from dysmorphology during development of the
renal system (Fig. 12-19B). The outcome for most
children with multicystic dysplastic kidney disease is
generally good because the disease is unilateral in
75% of the cases.
Development of
Urinary bladder
• Urogenital sinus is divided into:
• Vesical part that forms most of the urinary bladder
and is continuous with the allantois
• Pelvic part that becomes the urethra in the neck of
the bladder,
• Prostatic part of the urethra in males, and the entire
urethra in females
• Phallic part that grows toward the genital tubercle
(primordium of the penis or clitoris).
• The bladder develops mainly from the vesical part of the
urogenital sinus, but its trigone (triangular area at the base
of the bladder between the openings of the ureters) 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 of the urogenital sinus.
• Other layers of UB wall develop from adjacent splanchnic
mesenchyme.
Development of Urinary
bladder
•
•
•
Initially the bladder is continuous with
the allantois. The allantois constricts
and becomes a thick fibrous cord,
the urachus (median umbilical
ligament).
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 develop into the ejaculatory
ducts.
In females, the distal ends of the
mesonephric ducts degenerate.
Urachal Anomalies
•
•
•
In infants, a remnant of the urachal lumen may persist in
the inferior part of the urachus. In approximately 50% of
cases, the lumen is continuous with the cavity of the
bladder. Remnants of the epithelial lining of the urachus
may give rise to urachal cysts, which are not usually
detected except during a postmortem unless the cysts
become infected and enlarge.
The patent inferior end of the urachus may dilate to form
a urachal sinus that opens into the bladder. The lumen in
the superior part of the urachus may also remain patent
and form a urachal sinus that opens at the umbilicus.
Very rarely the entire urachus remains patent and forms
a urachal fistula that allows urine to escape from its
umbilical orifice.
Congenital Anomalies of the UB
CONGENITAL MEGACYSTIS
A pathologically large urinary bladder may result from a
congenital disorder of the ureteric bud, which may be
associated with dilation of the renal pelvis. The large bladder
may result from posterior urethral valves. Many infants die
from this disorder or suffer from renal failure in early
childhood.
Exstrophy of the bladder
Deficiency of the anterior abdominal wall, is caused by
incomplete median closure of the inferior part of the wall (Fig.
12-25). The defect involves both the abdominal wall and the
anterior wall of the urinary bladder; it results from failure of
mesoderm to migrate between the ectoderm and endoderm
of the abdominal wall
Development of Urethra
•
•
•
•
The epithelium of most of the male urethra
and the entire female urethra is derived from
endoderm of the urogenital sinus.
In males, the distal part of the urethra in the
glans of the penis is derived from a solid cord
of ectodermal cells that grows inward from the
tip of the glans and joins the rest of the
spongy urethra.
Consequently, the epithelium of the terminal
part of the urethra is derived from the surface
ectoderm.
The connective tissue and smooth muscle of
the urethra in both sexes are derived from
splanchnic mesenchyme.
Development of the suprarenal glands
•
•
•
Cortex develops from
mesenchyme.
Medulla from neural crest
cells from a sympathetic
ganglion.
During the 6th week, the
cortex begins as an
aggregation of
mesenchymal cells on
each side of the embryo
between the root of the
dorsal mesentery and the
developing gonad.
CONGENITAL ADRENAL HYPERPLASIA &
ADRENOGENITAL SYNDROME
Excessive androgen production
during the fetal period, due to
abnormal increase in the cells of the
suprarenal cortex results.
In females, this usually causes
masculinization of the external
genitalia.
Male infants have normal external
genitalia.
Later in childhood in both sexes,
androgen excess leads to rapid
growth and accelerated skeletal
maturation.