1. No category

Urinary System
J.-H. Lue
Primordium:
• intermediate mesoderm
• cloaca
• coelomic epithelium
1
3 w (18d)
4w (24d)
4w (26d)
2
Intermediate mesoderm
3
Intermediate mesoderm
intermediate mesoderm  urogenital ridge 
nephrogenic & genital (gonadal) ridges (cords)
4
Intermediate mesoderm
intermediate mesoderm  urogenital ridge 
nephrogenic & genital (gonadal) ridges (cords)
5
Pronephros
(4th week)
transitory , nonfunctional structures; analogous to the kidneys in primitive fishes
•located in cervical region
•its duct open into the cloaca
6
Mesonephros (4th
week)
7
amphibians; located caudal to the rudimentary pronephros
Development of nephrons
5w
mesonephric vesicle  S-shaped mesonephric tubule 
mesonephric (Wolffian) duct cloaca (urogenital sinus)
8
Development of nephrons
mesonephric
p
vesicle  S-shaped
p mesonephric
p
tubule 
mesonephric (Wolffian) duct cloaca (urogenital sinus)
• medial end of mesonephric tubule + blood capillaries
(glomerulus)  glomerular (Bowman‘s) capsule
9
Development of nephrons
5w
ureteric bud  a dorsal outgrowth from the mesonephric duct
near its entry into the cloaca (urogenital sinus)
ureteric
i bud
b d ( metanephric
h i diverticulum)
di
i l )  collecting
i system
metanephrogenic blastema ( metanephric mesoderm )excretory
10
Ureteric bud
1. primitive renal pelvis  major calyces 
minor calyces  collecting tubules
2. the stalk itself  ureter
11
Development
Development
of nephrons
of nephrons
metanephric (tissue) cap  metanephric vesicles  metanephric tubules
nephrons or excretory units (10-18th weeks , 32th week upper limit)
(i) proximal
i l endd  Bowman‘s
‘ capsule
l
(ii)distal end  proximal ＆ distal convoluted tubules, Henle‘s loop
12
Development of nephrons
8 week
20 weeks to 38 weeks
13
Genes involved in differention of the kidneys
14
Kidneys and suprarenal glands
28 w
-- normally has polylobar appearance due to the manner of
development of the ureteric bud in the metanephrogenic blastema
-- increase in kidney size: elongation of proximal convoluted tubules
& interstitial tissue
15
Positional changes of kidneys
6w
9w
th
changes in kidney position: 9 week
-- the
th metanephros
t
h
i iti ll is
initially
i located
l t d in
i the
th pelvic
l i
region but shifts later to a more cranial position in the
abdomen
16
Positional changes of kidneys
factors:
factors
(i) a diminution
di i ti off the
th body
b d curvature
t
(ii) growth of the body in the lumbar and sacral regions
effects:
17
(i) the kidney hilum initially faces ventrally
(ii) after ascent, the hilum is directed medially due to the 90º rotation of the kidney
Changes in the blood supply of the developing kidneys
18
．in the pelvis, the metanephros receives its arterial supply from
the branches of common iliac arteries
Changes in the blood supply of the developing kidneys
19
Changes in the blood supply of the developing kidneys
20
．during ascent to the abdomen, the kidney is vascularized by
arteries that originate from the aorta at continuously higher levels
Changes in the blood supply of the developing kidneys
21
．the lower vessels usually degenerate, except for vascular variations and anomalies
Various birth defects of the urinary stsystem
unilateral
renal agenesis
double and
ectopic
p ureter
Pelvic kidney
bilateral renal
agenesis
Pancake kidney
22
Abnormal location of the kidney
Pelvic kidney
Horseshoe kidney
23
Variations of renal vessels
24
Development of PUS
．weeks 44-7,
7 urorectal septum -- cloaca -- (i)
dorsal anorectal canal, and (ii) ventral
primitive urogenital sinus
．cloacal membrane -- (i) anal membrane, and
(ii) urogenital membrane
primitive urogenital sinus (PUS)
．cranial vesical part  urinary bladder 
allantois  urachus  median umbilical
lig.
g
．middle pelvic part: in male  prostatic
and membranous parts of the urethra; in
female  entire urethra
．caudal phallic part or definitive
urogenital
i l sinus
i
 penile
il urethra
h
25
Development of PUS
．weeks 4-7, urorectall septum -- cloaca
l
-- (i) dorsal anorectal canal,
and(ii) ventral primitive urogenital sinus
．cloacal membrane -- (i) anal membrane
membrane, and (ii) urogenital
membrane
26
primitive urogenital sinus (PUS)
．cranial vesical part  urinary bladder  allantois  urachus  median umbilical lig.
．middle
middle pelvic part: in male  prostatic and membranous parts of the urethra; in
female  entire urethra
．caudal phallic part or definitive urogenital sinus  penile urethra
27
Development of urinary bladder
28
Uurinary bladder
．epithelium -- derived from endoderm of cranial part of the PUS
．lamina propria, muscle layers and serosa -- develop from the adjunct splanchnic
mesenchyme
．caudal portion of mesonephric ducts  mucosa of trigone of bladder replaced by
endodermal epithelium of urogenital sinus
．caudal
caudal ends of mesonephric ducts  ejaculatory ducts
In the abdomen  infant & children; enter the pelvis major  six years of age; pelvis
minor  puberty
29
Development of urethra
．epithelium
ith li
off prostatic
t ti urethra
th
(PRU) proximal to the orifices of
the ejaculatory ducts -- derived
from the caudal part of the
mesonephric ducts
．epithelium
p
of the remainder of the
PRU and membranous urethra-develops from pelvic portion of
urogenital sinus
．epithelium of penile urethra -originates from phallic portion of
PUS with the exception of the
glandular portion
male urethra
．epithelium
p
of the gglandular
portion of penile urethra -develops by canalization of an
ectodermal plat of cells which 30
extends into the glans from its tip
Development of urethra
11 w
12 w
epithelium of penile urethra -- originates
f
from
phallic
h lli portion
ti off PUS with
ith the
th
exception of the glandular portion
14 w
31
epithelium
ith li
off th
the glandular
l d l portion
ti off penile
il urethra
th -develops by canalization of an ectodermal plat of cells
which extends into the glans from its tip
Urachal anomalies
Urachal cyst
Urachal sinus
Urachal fistula
32
Exstrophy
p y of
the bladder
33
epispadias
Development of suprarenal gland
．fetal cortex -- mesodermal origin mesenchymal cells (between the
root of the dorsal mesentery
y and the developing
p g ggonad),
), at 6th week
．medullary area -- ectodermal (neural crest) origin
34
Development of suprarenal gland
Newborn
4-year
1-year
．permanent cortex-- mesenchymal cell arises from the mesothelium and enclose the
fetal cortex; medullary area -- ectodermal (neural crest) origin
35
．differentiation of the characteristic suprarenal cortical zones begins during the late fetal period
Development of suprarenal gland
．zona golmerulosa and zona fasciculata -- present at birth
．zona reticularis -- not recognizable until about the end of the 3rd year
．fetal suprarenal gland adult gland 10 to 20 times
36
28 w
Development of the
urinary system
37
URINARY SYSTEM
Dr. J.-H. Lue Embryology
Primordium--derived from: 1) intermediate mesoderm; 2)cloaca and 3)coelomic
epithelium
FORMATION OF EXCRETORY UNIT
．intermediate mesoderm urogenital ridge nephrogenic & genital
(gonadal) ridges (cords)
．nephrogenic ridges  nephric structures
．nephric tubules
DEVELOPMENT OF THE KIDNEY
．pronephros (forekidney) --appears in the 4th week
-- transitory, nonfunctional structures; analogous to the kidneys in primitive fishes
-- located in cervical region
-- its duct open into the cloaca
．mesonephros (midkidney) or Wolffin body --appears later in 4th week,
(amphibians)
-- located caudal to the rudimentary pronephros —nephrogenic cord 
mesonephric vesicle  S-shaped mesonephric tubule  mesonephric
(Wolffian) duct cloaca (urogenital sinus)
-- medial end of mesonephric tubule  blood capillaries (glomerulus) 
glomerular (Bowman‘s) capsule
-- capsule + glomerulus  mesonephric (renal) corpuscle
-- as an interim kidney until the permanent kidney is established
．metanephros (hindkidney) or permanent kidney
．200 genes  WT1, BF-2, mouse kidney
．appears early in the 5th week
．begins to function 4 weeks later
．urine formation continues actively throughout fetal life
．develops from two sources:
(i) ureteric bud (metanephric diverticulum)  collecting system
(ii) metanephrogenic blastema (metanephric mesoderm) excretory system
collecting system
ureteric bud -- a dorsal outgrowth from the mesonephric duct near its entry into
the cloaca (urogenital sinus)
1
ureteric bud (i)  1)primitive renal pelvis  2)major calyces  3)minor calyces
 4)collecting tubules
(ii) the stalk itself  ureter
．differentiation of the collecting tubules depends on an induction stimulus
from the ureteric bud and metanephric mesoderm; N-linked
oligosaccharides appear to be important for this inductive interaction
excretory system
．metanephric (tissue) cap  metanephric vesicles  metanephric tubules
nephrons or excretory units (10-18th weeks , 32th week upper limit)
(Wnt-2 gene)
(i) proximal end  Bowman‘s capsule
(ii)distal end  proximal ＆ distal convoluted tubules, Henle‘s loop
．fetal kidneys
-- normally has polylobar appearance due to the manner of development of
the ureteric bud in the metanephrogenic blastema
-- increase in kidney size: elongation of proximal convoluted tubules &
interstitial tissue
．functions of kidney: 9th week
-- urine + amniotic fluid  mouth GI tract blood stream  placenta
maternal blood
-- during fetal life, not possible for excretion of waste products
changes in kidney position: 9th week
-- the metanephros initially is located in the pelvic region but shifts later to a
more cranial position in the abdomen
．factors: (i) a diminution of the body curvature
(ii) growth of the body in the lumbar and sacral regions
．effects: (i) the kidney hilum initially faces ventrally
(ii) after ascent, the hilum is directed medially due to the 900
rotation of the kidney
changes in the blood supply of the developing kidneys
．in the pelvis, the metanephros receives its arterial supply from the branches
of common iliac arteries
．during ascent to the abdomen, the kidney is vascularized by arteries that
originate from the aorta at continuously higher levels
．the lower vessels usually degenerate, except for vascular variations and
anomalies
2
ANOMALIES OF THE KIDNEYS AND URETERS
．renal agenesis -- unilateral and bilateral
．ectopic kidneys
．pelvic kidneys
．pancake kidney
．unilateral fused kidney
．horseshoe kidney
．duplications of the urinary tract
．double and ectopic ureter
DEVELOPMENT OF THE BLADDER AND URETHRA
weeks 4-7, urorectal septum cloaca (i) dorsal anorectal canal, and(ii) ventral
primitive urogenital sinus
．cloacal membrane (i) anal membrane, and (ii) urogenital membrane
Primitive urogenital sinus (PUS)
．cranial vesical part  urinary bladder  allantois  urachus  median
umbilical lig.
．middle pelvic part: in male  prostatic and membranous parts of the
urethra; in female  entire urethra
．caudal phallic part or definitive urogenital sinus penile urethra
．urinary bladder
．epithelium -- derived from endoderm of cranial part of the PUS
．lamina propria, muscle layers and serosa -- develop from the adjunct splanchnic
mesenchyme
．caudal portion of mesonephric ducts  mucosa of trigone of bladder
replaced by endodermal epithelium of urogenital sinus
．caudal ends of mesonephric ducts  ejaculatory ducts
．in the abdomen-- infants and children; enter the pelvis major-- six years of age;
pelvis minor-- puberty
．male urethra
．epithelium of prostatic urethra (PRU) proximal to the orifices of the
ejaculatory ducts -- derived from the caudal part of the mesonephric ducts
．epithelium of the remainder of the PRU and membranous urethra-- develops
from pelvic portion of urogenital sinus
．epithelium of penile urethra -- originates from phallic portion of PUS with the
exception of the glandular portion
．epithelium of the glandular portion of penile urethra -- develops by
canalization of an ectodermal plat of cells which extends into the glans from
3
its tip
．lamina propria -- forms from adjacent splanchnic mesenchyme
．female urethra
．epithelium of entire urethra -- derived from endodermal origin of middle part
of PUS
．Lamina propria and smooth muscle layers -- develop from adjacent splanchnic
mesenchyme
．anomalies
．urachal anomalies
．urachal fistula
．urachal cyst
．urachal sinus
．exstrophy of the bladder
．epispadias
SUPRARENAL (ADRENAL) GLAND
．fetal cortex -- mesodermal origin mesenchymal cells (between the root of
the dorsal mesentery and the developing gonad), at 6th week mesothelium
lining posterior abdominal wall
．permanent cortex-- mesenchymal cell arises from the mesothelium and
enclose the fetal cortex
．medullary area -- ectodermal (neural crest) origin
．differentiation of the characteristic suprarenal cortical zones begins during the
late fetal period
．zona golmerulosa and zona fasciculata -- present at birth
．zona reticularis -- not recognizable until abort the end of the 3rd year
．fetal suprarenal gland adult gland 10 to 20 times
4