Download Development of The Kidney

 Objectives
Development Of The Kidney.
Describe the development of kidney.
Pronephros.
Mesonephros.
Metanephros.
Discuss the congenital anomalies of
kidney.
UROGENITAL SYSTEM
General Overview:
Is derived from intermediate
mesoderm:
As the embryo folds, the intermediate
mesoderm loses its connection with
the somite and becomes the
urogenital ridge.
Nephrogenic cord gives rise to the
urinary system.
Gonadal ridge gives rise to the
reproductive system.
The Urinary
System
Three distinct
embryonic
"kidneys"
develop in a
cranial to caudal
direction:
1.Pronephros.
2. Mesonephros.
3. Metanephros.
Pronephros:
 Forms at the
beginning of the
fourth week.
 Represented by 7 to
10 solid cell groups
in the cervical
region.
 These groups form
vestigial excretory
units,nephrotomes.
By the end of the
fourth week, all
indications of the
pronephric system
have disappeared.
Mesonephros:
The mesonephros and
mesonephric ducts are derived
from intermediate mesoderm
from upper thoracic to upper
lumbar (L3) segments.
 In the fourth week first excretory tubules of the
mesonephros appear.
 A glomerulus forms at their medial extremity. Around
the glomerulus, the tubules form Bowman’s capsule,
and together these structures constitute a renal
corpuscle.
 Laterally,the tubule enters the longitudinal collecting
duct known as the mesonephric or wolffian duct.
 While caudal tubules
are still
differentiating,cranial
tubules and glomeruli
degenerate.
 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.
 They disappear in the
female.
 Metanephros:
 The third urinary organ, the
metanephros or permanent
kidney, appears in the fifth
week.
 Its excretory units develop
from metanephric mesoderm
in the same manner as in the
mesonephric system.
 The development of the duct
system differs from that of
the other kidney systems.
 The caudal
porton of the
mesonephric
duct produces a
ureteric bud.
The ureteric
bud surrounded
by a cap of
mesenchyme.
 The ureteric
bud will give:
Ureter.
Renal pelvis.
Calyces.
 Collecting
tubules.
The cap of the metanephric
mesenchyme will give the:
 Bowman’s capsule.
 Proximal convoluted tubule.
 Ascending & descending of Henle’s
loop.
 Distal convoluted tubule.
 The kidney "migrates" from its
original location in the pelvis up into
the abdominal cavity.
 All nephrons are present at birth.
Disorder of the number of kidneys
Renal agenesis:
Renal agenesia can occur uni- or bilaterally, isolated or
combined with other abnormalities (1/4 of all renal agenesias
are associated with genital abnormalities,
Too many kidneys (doubling)
This congenital anomaly is extremely rare. Involved is an independent
kidney with its own vascular supply, a capsule and its own urinary tract. The
cause is a very early division of the ureter bud.
Rotationsanomalis
This anomaly is relatively frequent. One speaks of a malrotation if the pyeloureteral connection is oriented ventrally (missing rotation), dorsally (rotation of
more than 90°) or laterally (inverse rotation). The kidney and urinary tract are
here anatomically and histologically normal. Sometimes, though, one observes
anomalies in the connections between ureter and renal pelvis, which can lead to
a hydronephrosis
Disorder of the ascent of the kidneys or ectopic kidneys
A kidney is ectopic when, without ptosis, it does not lie in the lumbar
fossa. The ectopia is the result of an incomplete or missing ascent. It
can occur in the upper or lower region (pelvic kidney) or even crossed.
In a crossed ectopia a kidney migrates to the other side. Its ureter
crosses the midline and inserts normally into the bladder. The
crossed ectopia can occur unilaterally or bilaterally. In the case of a
unilateral crossed ectopia a fusion of the two kidneys often occurs.
Ectopias are normally asymptomatic.
Horseshoe kidney
Its incidence is around 1/600. It is assumed that it arises due to a
joining of both kidneys from both sides and during the 5th week
when both organs still lie very close together in the small pelvis.
The two kidneys are most often bound together at the lower pole.
 Abnormal kidney size.
Hypoplasia:
It results from an embryonic developmental stop
of the kidney, the structure of which is otherwise
normal.. The kidney is small, whereby the renal
hypoplasia must be distinguished from a
secondary atrophic kidney, resulting from an
infection (chronic pyelonephritis).
Aplasia:
In an aplastic kidney, a fibroused kidney anlage
with its own derivates of the mesonephric duct
(Wolffian duct) is present. It represents the
extreme form of a renal dysplasia and differs
from agenesia, in which absolutely no kidney
primordium exists.
Polycystic kidneys:
A renal dysplasia must be distinguished from a simple hypoplasia in which
the histological structure is normal. Renal dysplasia is characterized by a
congenital anomaly of embryonic renal tissue development. The kidneys
develop large epithelial cysts that are localized in the renal parenchyma and
lead to the loss of the functional tissue, which can end in renal insufficiency.
Vascular anomalies of the kidney:
There are many arterial and venous variants of the renal
blood supply, reflected in the changing blood supply of the
migrating kidneys during their development.
Congenital ureteral abnormalities
Course anomalies of the ureter:
Retrocaval / retroiliac ureter:
In this abnormality the right ureter traces out an "S" at the L4 level
behind the vena cava (retrocaval ureter).
Anomalies of the ureteral diameter
Primary megaloureter due to an obstruction:
The cause of this abnormality is a constriction in the terminal part
of the ureter, leading to a dilatation.
Abnormal number of ureters
Disorders in the number of ureters belong to the most frequent anomalies of
the urinary tract, whereby they are often asymptomatic. They arise from a
premature branching of the ureter bud.
Complete doubling:
Here a complete doubling of the ureters with a second renal
pelvis is involved. The ureters empty into the bladder.