The document outlines the development of the urinary system, which originates from the intermediate mesoderm and progresses through three phases: pronephros, mesonephros, and metanephros. It details the formation and degeneration of these kidney structures, as well as the development of the urinary bladder and urethra, highlighting the roles of different embryonic tissues. Additionally, the document discusses the formation of the suprarenal gland and its cellular origins.

1. NormalDevelopmentofUrinarySystem
By
Hassaan Ali Gad
Assistant lecturer of urology
Aswan University

2. • The urinary system develops from the intermediate
mesoderm which extends along the dorsal body wall of the
embryo
• A longitudinal elevation of mesoderm forms on each side of
the dorsal aorta – The Urogenital Ridge. This ridge gives rise
to parts of the urinary system which is the nephrogenic cord
or ridge.
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7. • The Urinary system goes through three phases on its way to becoming
fully functioning :
• 1- Pronephros
• 2- Mesonephros
• 3- Metanephros
• Starting from 4th wk & end on 36 wk of intra uterine
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9. • PRONEPHROI:
• These transitory, nonfunctional structures appear in the 4th week The
pronephroi are represented by a few cell clusters and tubular structures in
the neck region.
• The pronephros develops as five to seven paired segments in the region of
the future neck and thorax
• The pronephric ducts run caudally and open into the cloaca.
• The rudimentary pronephroi soon degenerate. Most of the pronephric
ducts persist and are utilized by the next set of the kidneys.
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10. Development of pronephros and mesonephros.
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11. • MESONEPHROI
• These large; elongated; excretory organs appear late in the 4th week
caudal to the rudimentary pronephroi.
• They are well developed and function as inteim kidneys for about 4 weeks.
• It consists of glomeruli and mesonephric tubules. These tubules open into
the mesonephric ducts. The mesonephric ducts open into the cloaca.
• The mesonephroi degenerate toward the end of the first trimester.
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13. Metanephroi
• The primordia of permanent kidneys begin to develop early in
the 5th week and start to function about 4 weeks later. The
permanent kidneys develop from 2 sources,
• the metanephreic diverticulum ( ureteric bud )
• the metanephric mass ( metanephrogenic blastema ).
• The metanephric diverticulum is an outgrowth from the
mesonephric duct near its entrance into the cloaca. The
metanephric mass of the intermediate mesoderm is derived
from the caudal part of the nephrogenic cord. Both primordia
of the metanephros are mesodermal origin.
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15. • Metanephric diverticulum;( ureteric bud )
• It is the primordium of the ureter; renal pelvis; calices
and collecting tubules. As it elongates, it penetrates the
metanephric mass of the intermediate mesoderm. The
stalk of it becomes the ureter and its expanded cranial
end forms the renal pelvis.
• The renal corpuscle ( glomerulus and glomerular capsule
) and its proximal convoluted tubules; nephron loop ( of
Henle ) and distal convoluted tubule constitute a
nephron.
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16. The straight collecting tubules undergo repeated branching,
forming generations of tubules. The first 4 generations enlarge
and become confluent to form the major calices. The 2nd four
generations coalesce to form the minor calices. The remaining
generations of tubules form the collecting tubules.
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17. The end of each arched collecting tubule induces clusters of mesenchymal
cells in the metanephric mass of mesoderm to form metanephric vesicles.
These vesicles elongate and become metanephric tubules.
The proximal ends of these tubules are invaginated by glomeruli. Between the
10th & 18th weeks of gestation, the number of the glomeruli increases until
the 32 week, when an upper limit is reached. Their filtration begins around
the 9th fetal week and the rate of filtration increases after birth.
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18. • A uriniferous tubule:
• It consists of 2 different parts
1.Nephron from the metanephron mass of intermediate
mesoderm. The nephron formation is complete at birth.
2- Collecting tubule from the metanephric diverticulum.
• The metanephric diverticulum and the metanephric mass
of intermediate mesoderm interact and induce each other
by a process known as reciprocal induction to form the
permanent kidneys.
• Transformation of the metanephric mesenchyme to
epithelial cells of the nephon ( mesenchymal- epithelial
transition ) is regulated by factors secreted by the
metanephric diverticulum.
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20. Positional Changes of Kidneys
• Initially the metanephric kidneys lie close to each other in the pelvis
ventral to the sacrum.
• As the abdomen and pelvis grow, caudal to the kidneys, so that they
occupy more cranial level. They gradually come to lie in the abdomen and
move farther apart and attain their adult position by 9th week.
• Initially the hilum faces ventrally, however, as the kidney ascends it rotates
medially 90 degrees. By the 9th week the hilum is directed anteromedially.
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22. Renal Vascular Development
• Angiogenic Hypothesis- derived from
branches off aorta and other pre-existing
extrarenal vessels.
• Vasculogenic Hypothesis- originate in situ
from vascular progenitor cells (VEGF).vascular endothelial growth factor
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23. Development of Urinary Bladder
• Division of the cloaca by urorectal septum into dorsal rectum and a
ventral urogenital sinus.
• The urogenital sinus is divided into 3 parts:
• 1- A cranial vesical part that forms most of the bladder and is
continuous with the allantois.
•
• 2- A middle pelvic part that becomes the urethra in the bladder
neck and the prostatic part of
urethra in male and the entire urethra in females.
• 3- A caudal phallic part that grows toward the genital tubercle.
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24. • It develops from 3 parts:
– Vesico-urethral canal (endodermal): forms most of the
bladder.
– Proximal part of allantois (endodermal): forms apex of
the bladder, rest of allantois is called urachus. Later the
urachus becomes obliterated to be median umbilical
ligament.
– Caudal parts of both mesonephric ducts: forms the
trigone of the bladder
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26. • Initially the bladder is continuous with the allantois.
The allantois become constricted and form a thick
fibrous cord, the urachus which extends from the apex
of the bladder to the umbilicus.
• In the adult the urachus is represented by the median
umbilical ligament which is attached to the apex of the
bladder and extends along the posterior surface of the
anterior abdominal wall .
• The median umbilical ligament lies between the medial
umbilical ligaments which are the fibrous remnants of
the umbilical arteries.
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27. • The caudal ends of mesonephric ducts become
the ejaculatory ducts. The orifices of these ducts
move close together and enter the prostatic part
of the urethra.
• In infants and children the urinary bladder, is in
the abdomen when it is empty. It begins to
enter the greater pelvis at about 6 years of age.
It enters lesser pelvis and become a pelvic organ
at or even after puberty.
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31. Development of Urethra
• The epithelium of most of the male urethra is derived from the
endoderm of the phallic part of the urogenital sinus. The epithelium
of the terminal part of the urethra is derived from the surface
ectoderm.
• The entire female urethra is derived from endoderm of the
urogenital sinus.
• The distal part of the spongy urethra in the glans of the penis is
derived from a solid cord of ectodermal cells which is derived from
the surface ectoderm. These cells grow from the tip of the glans
and joins the rest of the spongy urethra. So, the spongy urethra has
a dual origin.
• The connective tissue and smooth muscle of the urethra in both
sexes are derived from splanchnic mesenchyme.
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32. • Female Urethra: is developed mostly from vesico-urethral canal
(cranial part of primitive uro-genital sinus).
• Male Urethera: Is composed of 3 parts:
– Prostatic urethera: is developed from vesico-uretheral canal and
absorbed mesonephric duct (upper 1/2) as well as pelvic part of
defenitive uro-genital sinus (lower 1/2). 15 buds from the wall of
urethera form the prostate gland by 12th week.
– Membranous urethera: from pelvic part of defenitive uro-
genital sinus.
– Penile urethera: most of penile urethera is developed from
phallic part of defenitive uro-genital sinus by the formation of
uretheral plate then canal. Part of penile urethera in galns penis
is developed from surface ectoderm. Two buds from proximal
part of penile urethera will form bulbo-uretheral glands.
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35. Development of the Suprarenal Gland
• The medulla develops from neural crest cells that
derived from an adjacent sympathetic ganglion.
• The cortex develops from mesodermal cells which is
first indicated during the 6th weeks by an aggregation
of mesenchymal cells on each side, between the root
of the dorsal mesentery and the developing gonad.
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37. • Initially the neural crest cells form a mass on the
medial side of the fetal cortex. As they are
surrounded by the fetal cortex, these cells
differentiate into the secretory cells of the medulla.
• Later more mesenchymal cells arise from the
mesothelium lining the posterior abdominal wall and
enclose the fetal cortex. These cells give rise to the
permanent cortex.
• Differentiation of the suprarenal cortical zones begin
during the late fetal period.
• The zona glomerulosa and the zona fasciculata are
pressent at birth, but the zona reticularis is not
recognizable until the end of the third year.
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