3. Urinary and genital
systems are closely
associated
Both develop from
intermediate mesoderm
4. Excretory duct of
both system enter
into a common
cavity,the cloaca.
5. The urinary system
begins to develop
before the genital
system and consists
of: The kidneys, which
excrete urine
The ureters, which
convey urine from the
kidneys to the urinary
bladder
The urinary bladder,
which stores urine
temporarily
The urethra, which
carries urine from the
bladder to the exterior
of the body
6. DEVELOPMENT OF KIDNEY AND URETER
At the 3rd wk( approximately at
17th day, intra-embryonic
mesoderm differentiate into
A .Paraxial mesoderm
B intermediate mesoderm
C Lateral plate mesoderm
cells close to the midline
proliferate and form a thickened
plate of tissue known as Paraxial
mesoderm Paraxial mesoderm
form Somites
A number of cleft appear within
the lateral plate .The clefts
coalescence to form a single
cavity known as intraembyonic
coelom.
The coelomic cavity divide
lateral plate mesoderm into two
layers . (a) a layer continuous
with mesoderm covering the
amnion, known as the somatic
or parietal mesoderm layer, and
(b) a layer continuous with
mesoderm covering the yolk
sac, known as the splanchnic or
visceral mesoderm layer.
Intermediate mesoderm
connects paraxial and lateral
plate mesoderm .
7. Intermediate
Mesoderm
Intermediate
mesoderm, which
temporarily connects
paraxial mesoderm
with the lateral plate ,
differentiates into
urogenital structures.
In cervical and upper
thoracic regions, it
forms segmental cell
clusters (future
nephrotomes),
whereas more
caudally, it forms an
unsegmented mass of
tissue, the
nephrogenic cord.
8.
9. Kidney Systems
Three slightly
overlapping kidney
systems are formed in
a cranial-to-caudal
sequence during
intrauterine life in
humans: the
pronephros,mesone
phros, and
metanephros.
The first of these
systems is rudimentary
and nonfunctional;
the second may
function for a short
time during the early
fetal period;
the third forms the
permanent kidney.
10. Pronephros
At the beginning of the
fourth week, the
pronephros is
represented by 7 to 10
solid cell groups in the
cervical region.
These groups form
vestigial excretory
units, known as
nephrotomes.
11. PRONEPHROS
In the cervical region, cranial part of the
nephrogenic cord is segmented to form
7 to 10 nephrotome which become
cavitated to form 7 to 10 pronephric
tubule.
Each tubule has two end ..Lateral end of
tubules join to form pronephic duct.
Medial end open into coelomic cavity.
Pronephric duct opens into ventral part
of cloaca which is subsequently develop
into the urinary bladder.
Pronephric tubules and poximal part of
duct degenerates leaving the caudal part
of duct as mesonephric duct.
12.
13. MESONEPHROS
About 70-80
mesonephric tubules
are derived from
intermediate
mesoderm from upper
thoracic to upper
lumbar (L3) segments
.
Early in the fourth
week of development,
during regression of
the pronephric system,
the first excretory
tubules of the
mesonephros appear.
14. Each mesonephric tubule is placed horizontally
.Its lateral end opens into the pronephric duct
which is now named as mesonephric or walfian
duct.
The medial end form a dilated blind end which
is indented to form Bowmans capsule which
receive an internal glomerulus from the lateral
branches of dorsal aorta.
The tubule become -S- shaped. Bowman
capsule together with glomerulus form renal
corpuscle.
15. Ureteric
bud
Excretory tubules
of the pronephric
and mesonephric
systems in a 5-
week-old embryo.
Note the longitudinal
collecting duct, formed
initially by the
pronephros but later by
the mesonephros
16. • In the middle of the second month the
mesonephros forms a large ovoid organ
on each side of the midline.
• Since the developing gonad is on its
medial side, the ridge formed by both
organs is known as the urogenital
ridge.
• The caudal tubules are still
differentiating,
• The cranial tubules and glomeruli show
degenerative changes, and by the end
of the second month the majority have
disappeared.
• In the male a few of the caudal tubules
and the mesonephric duct persist and
participate in formation of the genital
system, but they disappear in the
female.
17. METANEPHROS
• The third urinary
organ, the
metanephros, or
permanent
kidney, appears in
the fifth week.
• .
18. The permanent kidneys develop from
two sources.
The metanephric diverticulum (ureteric
bud) and The metanephrogenic
blastema or metanephric mass of
mesenchyme
The metanephric diverticulum is an
outgrowth from the mesonephric duct
near its entrance into the cloaca, and
the metanephrogenic blastema is
derived from the caudal part of the
nephrogenic cord .
As it elongates, the metanephric
diverticulum penetrates the
metanephrogenic blastema-a mass of
mesenchyme
The stalk of the metanephric
diverticulum becomes the ureter
19. Collecting System
• Collecting ducts of the permanent kidney
develop from the ureteric bud.
• The bud penetrates the metanephric tissue.
• The bud dilates, forming the primitive renal
pelvis, and splits into cranial and caudal
portions (the future major calyces).
• Each calyx forms two new buds while
penetrating the metanephric tissue.
• These buds continue to subdivide until
12 or more generations of tubules have
formed.
• Meanwhile, at the periphery more tubules
form until the end of the fifth month
20. • The tubules of the second order enlarge
and absorb those of the third and
fourth generations, forming the minor
calyces of the renal pelvis.
• Collecting tubules of the
fifth and successive
generations form the
renal pyramid.
• The ureteric bud gives rise to the;
– ureter,
– renal pelvis,
– major and minor calyces,
– 1 million to 3 million collecting
tubules
21. Excretory System
• Each newly formed collecting tubule is
covered at its distal end by a metanephric
tissue cap.
• Cells of the tissue cap form small vesicles, the
renal vesicles.
• The one end of the vesicle abuts on the
collecting tubule of the ureteric bud
separated at first by a bilaminar partition
• .The other end of the vesicle is dilated and
invaginated by the internal glomerulus which
is developed from the nephrogenic cord.
• Renal vesicles give rise to small S-shaped
tubules.
• These tubules, together with their glomeruli,
form nephrons.
• The proximal end of each nephron forms
Bowman’scapsule.
22. The proximal end of each nephron forms
Bowman’s capsule. Continuous lengthening of
the excretory tubule results in formation of the
proximal convoluted tubule, loop of Henle,
and distal convoluted tubule.
Finally the blind end(distal end) of the
excretory tubules and collecting tubules are
fused and partition between them disappear
and the metanephric kidney starts
functioning.
23. • The kidney develops from two
sources:
– (a) metanephric mesoderm,
which provides excretory units.
– (b) the ureteric bud, which gives
rise to the collecting system.
• Nephrons are formed until
birth, at which time there
are approximately 1 million
in each kidney.
• Urine production begins early in
gestation, soon after differentiation of
the glomerular capillaries, which start
to form by the10th week.
• At birth the kidneys have a
lobulated appearance, but the
lobulation disappears during
infancy as a result of further
growth of the nephrons,
although there is no increase in
their number
24.
25.
26. URETER
Two fusiform enlargements appear at
the lumbar and pelvic levels of the
ureter at 5 and 9 months respectively
(the pelvic enlargement is inconstant).
As a result the ureter shows a
constriction at its proximal end
(pelviureteric region) and another as it
crosses the pelvic brim.
A third narrowing is always present at
its distal end and is related to the
growth of the bladder wall.
At first the distal end of the ureter is
connected to the dorsomedial aspect of
the mesonephric duct, but, as a result
of differential growth, this connection
comes to lie lateral to the duct.
Dorsal views of the bladder showing
the relation of the ureters and
mesonephric ducts during
development.
27.
28. Ascent of the kidneys
During the 5th and 6th weeks of development, the
mature kidneys lie in the pelvis with their hila
pointed anteriorly.
-As the pelvis and abdomen grow, the kidneys slowly
move upward.
-By the 7th week, the hilum points antero-medially
and the kidneys are located in the abdomen.
-As the embryo continues to grow in a caudal
direction, the kidneys come to lie in a retroperitoneal
position at the level of L1 by the 9th week of
development.
29. ASCENT OF THE KIDNEY
• The kidney, initially in the pelvic
region, The metanephric kidney is
initially sacral
• later shifts to a more cranial position
in the abdomen.
• This ascent of the kidney is caused
by diminution ofbody curvature and
by growth of the body in the lumbar
and sacral regions And due to the
ureteric outgrowth.
• In the pelvis the metanephros
receives its arterial supply from a
pelvic branch of the aorta.
• During its ascent to the abdominal
level, it is vascularized by arteries
that originate from the aorta at
continuously higher levels.
• The lower vessels usually
degenerate, but some may remain.
30. ROTATION
Initially the hilum of the kidney
faces ventrally; however, as the
kidney relocates (ascends), it
rotates medially almost 90
degrees.
By the ninth week, the hilum is
directed anteromedially .
Eventually the kidneys become
retroperitoneal (external to the
peritoneum) on the posterior
abdominal wall.
39. HORSESHOE KIDNEY
Sometimes, the lower poles fuse,
forming a horseshoe kidney . The
horseshoe kidney is usually at the
level of the lower lumbar
vertebrae, since its ascent is
prevented by the root of the
inferior mesenteric artery .
The ureters arise from the anterior
surface of the kidney and pass
ventral to the isthmus in a caudal
direction. Horseshoe kidney is
found in 1/600 .
40. Accessory renal
arteries are common;
they derive from the
persistence of
embryonic vessels
that formed during
ascent of the
kidneys. These
arteries usually arise
from the aorta and
enter the superior or
inferior poles of the
kidneys
41.
42. Malrotated Kidney.
Malrotated Kidney If a
kidney fails to rotate, the
hilum faces anteriorly, that
is, the fetal kidney retains
its embryonic position . If
the hilum faces posteriorly,
rotation of the kidney
proceeded too far; if it
faces laterally, lateral
instead of medial rotation
occurred. Abnormal
rotation of the kidneys is
often associated with
ectopic kidneys.
43. Duplications of the Urinary Tract
Duplications of the abdominal
part of the ureter and the renal
pelvis are common. These
anomalies result from division of
the metanephric diverticulum.
The extent of the duplication
depends on how complete the
division of the diverticulum was.
Incomplete division of the
metanephric diverticulum results
in a divided kidney with a bifid
ureter.
Complete division results in a
double kidney with a bifid ureter
or separate ureters
. A supernumerary kidney with
its own ureter, which is rare,
probably results from the
formation of two metanephric
diverticula.
44. Duplications of the URETER
Duplication of the ureter results
from early splitting of the ureteric
bud .
Splitting may be partial or
complete, and metanephric tissue
may be divided into two parts,
each with its own renal pelvis and
ureter.
In rare cases, one ureter opens
into the bladder, and the other is
ectopic, entering the vagina,
urethra, or vestibule
This abnormality results from
development of two ureteric buds.
One of the buds usually has a
normal position, whereas the
abnormal bud moves down
together with the mesonephric
duct. Thus it has a low, abnormal
entrance in the bladder, urethra,
vagina, or epididymal region
