Urogenital system
The urogenital system can be divided into
two entirely different components: the
urinary system and the genital system.
Two embryonic structures that play an
important role in the development of the
urogenital system are the intermediate
mesoderm and the cloaca.
We know that the mesoderm( or intra-
embryonic mesoderm is subdivided into:
(a) paraxial mesoderm
(b) an intermediate mesoderm;
(c) lateral mesoderm
The development of Urinary System
KIDNEY SYSTEMS
Kidney has passed three stages of evolution in a cranial to caudal sequence.
Pronephros
mesonephros
metanephros.
Pronephros
At the beginning of the fourth week, the pronephros is represented by 7 to 10 solid cell groups in the cervical region of nephrogenic cord.
These groups form vestigial excretory units, which are made up of pronephric tubules and a single desending pronephric duct. The human pronephros have no-function and disappear by the end of the fourth week.
But pronephric duct ending in the cloaca, however, persists. Then it become to mesonephric ducts after development of mesonephros.
• The mesonephros consist of a series of
excretory tubules that develop in the
thoracolumlar region. These tubules
(mesonephric tubules ) drain into the
nephric duct which may now are called the
mesonepheric duct.
Mesonephros
Mesonephros
mesonephric tubules( S-shaped )-Bowman’s C+Cap
mesonepheric duct
Cloaca
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 urogenital ridge
• Most of the mesonepheric tubules
disappear, but most part of them are
modified and take part in forming the duct
system of the testis. but they disappear in
the female.
• The metanephros, or permanent kidney,
appears in the fifth week. It arises from two
distinct sources. the metanephric blastema
and the ureteric bud
Metanephros
• The excretory dubules (or nephrons ) are
derived from the lower part of the
nephrogenic cord.This part is the
metanephros, the cells of which form the
metanephric blastema.
• The collecting part of the kidney is
derived from a diverticulum called the
ureteric bud which arises from the
lower part of the mesonephric duct
where it close to its entrance to the
cloaca.
The bud penetrates the metanephric tissue,
which cover the distal end of the bud as a
cap. Subsequently the bud grows and dilates
to form ampulla.The ampulla divides
repeatdly. The first three to five generations
of branches fuse to from the pelvis of the
kidney.the next divisions become the major
calyces while further divisions form the
minor calyces and collecting tubules.
The ureteric bud gives rise to the ureter, the
renal pelvis, the major and minor calyces,
and approximately 1 million to 3 million
collecting tubules.
Each newly formed collecting tubule is
covered at its distal end by a metanephric
tissue cap. Under the inductive influence of
the tubule, cells of the tissue cap form the
nephron.
• A solid clump of cells is converted into a
vesicle which soon becomes pear shaped
and opens into the ampulla. The visicle now
becomes an S-shapd tube. Its distal end
comes to be invaginated by a tuft of
capillaries which form a glomerulus.The
various parts of the nephron are derived
from this S-shaped tube.
• Capillaries grow into the pocket at one end
of the S and differentiate into glomeruli.
These tubules, together with their
glomeruli, form nephrons, or excretory
units.
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• POSITION OF THE KIDNEY
The kidney, initially in the pelvic region,
later shifts to a more cranial position in the
abdomen. This ascent of the kidney is
caused by diminution of body curvature and
by growth of the body in the lumbar and
sacral regions.
• BLADDER AND URETHRA
Urinary bladder and urether are derived from the cloaca.
cloaca urorectal septum
urogenital sinus
Primitive rectum
•Between the two, the tip of the urorectal septum forms the perineal body.
Cloacal
Membrane
urorectal septum
urogenital membrane
anal membrane
The Vessico urethral canal
The phallic part
urinary bladder
The pelvic part
Derivatives of two parts of Primitive urogenital sinus
Primitive urethra
Definitive UGS
The prostatic and membranous parts of the urethra in male
Urethra in female
The phallic part
urinary bladder
The pelvic part
Derivatives of two parts of Primitive urogenital sinus
Penile urthra in male
Vestibule in female
Primitive urethra
urinary bladder
The upper and largest part is the urinary
bladder.Initially the bladder is continuous
with the allantois, but when the lumen of
the allantois is obliterated, a thick fibrous
cord, the urachus, remains and
connects the apex of the bladder with the
umbilicus. In the adult, it is known as the
median umbilical ligament.
During differentiation of the cloaca, the caudal portions of the mesonephric
ducts are absorbed into the wall of the urinary bladder. Consequently, the ureters, initially outgrowths from the mesonephric ducts, enter the bladder separately.
As a result of ascent of the kidneys, the
orifices of the ureters move farther
cranially; those of the mesonephric ducts
move close together to enter the prostatic
urethra and in the male become the
ejaculatory ducts.
• Anomalies of kidneys: 1. Agenesis
2. Duplication:
3. Anomalies of shape:Horseshoe kidney
4. Abnormal of position:
5. Congenital polycystic kindney:
• Congenital polycystic kindney:
• Failure of the excretory tubules of the
metanephros to establish contact with the
collecting tubules, leads to the formation of
cysts. Isolated cysts are commonly seen,but
sometimes the whole kidney is a mass of
such cysts.The cysts press upon normal
renal tissue and destroy it.
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