The kidneys develop from intermediate mesoderm and progress through three stages - pronephros, mesonephros and metanephros. The metanephros forms the permanent kidneys. It develops from interaction between the ureteric bud and metanephric mesenchyme. Nephrons develop from mesenchyme and the collecting system from the ureteric bud. The kidneys ascend during development due to body growth. Common anomalies include horseshoe kidney and abnormal rotation or position of the kidneys.

1. EMBRYOLOGY OF KIDNEY
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2. EMBRYOLOGY OF
KIDNEY
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EMBRYOLOGY OF
KIDNEY
• Develop from a common mesodermal
ridge (intermediate mesoderm) along
the posterior wall of the abdominal cavity.
– pronephros, (rudimentary and
nonfunctional)
– mesonephros, (function for a short time
during the early fetal period)
– metanephros, (forms the permanent
kidney)

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PRONEPHR
OS
• At 3rd week of gestation
• Develops as five to seven solid cell groups
• starts at the cranial end of the nephrogenic
cord and progresses caudally
• As each tubule matures it immediately begins
to degenerate along with the segment of the
nephric duct

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MESONEPH
ROS
• Around 24th day, mesonephric vesicles begin to
form.
– Initially, several spherical mass of cells
– vesicle elongates, form an S-shaped tubule.
– The lateral end forms a bud that connects with
the nephric duct.
– The medial end lengthens and enlarges to form a
cup- shaped sac, which eventually wraps around
a knot of glomerular capillaries to form a renal
corpuscle.
• The tuft of glomerular capillaries originating from a
branch of the dorsal aorta invades the developing

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• Ducts fuse with the cloaca and begin to form
a lumen at the caudal end and progresses
cranially
• This differentiation progresses caudally
and results in the formation of 40 to 42
pairs of mesonephric tubules,
• At any time only 30 pair tubules
present,because degeneration start

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– By the 4th month, the human mesonephros -
completely disappeared, except for a few elements
that persist as
part of the reproductive tract.
– In males, some cranially located mesonephric
tubules become the efferent ductules of the testes
, epididymis and vas deferens
.
– In females, small, nonfunctional mesosalpingeal
structures
termed the epoöphoron and paroöphoron.

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METANEPHR
OS
• The definitive kidney
• Excretory units develop from metanephric mesoderm
• Ureteric bud forms from distal portion of the nephric
duct as sprouting buds
• Ureteric bud come in contact with the condensing
blastema of metanephric mesenchyme = 28th day
• The ureteric bud penetrates the metanephric mesenchyme
and
begins to divide dichotomously.
• As the ureteric bud divides and branches ,it gives
metanephros a lobulated appearance

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• Mesenchymal-epithelial interaction --
induce formation of future nephrons
• Glomerulus, proximal tubule, loop of
henle, and distal tubule = derive from
the metanephric mesenchyme
• Collecting system, consisting of
collecting ducts, calyces, pelvis, and
ureter, is formed from the ureteric bud

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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.
• Renal vesicles give rise to small S-shaped tubules.
• Capillaries grow into the pocket at one end of tubule
and differentiate into glomeruli.
• These tubules, together with their glomeruli, form nephrons,
or
excretory units.
• Theproximal end of each nephron forms Bowman’scapsule.

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• The distal end forms an open connection with one of the
collecting tubules, establishing apassagewayfrom Bowman’s
capsuleto the collecting unit.
• Continuous lengthening of the excretory tubule results in
formation of the proximal convoluted tubule, loop of Henle,
and distal convoluted tubule.
• At birth there are approximately 1 million of nephrons in each
kidney.
• Urine production begins early in gestation, soon after
differentiation of the glomerular capillaries, which start to
form by the 10th week.
• At birth the kidneys have a lobulated appearance, which
disappears during infancy as a result of further growth of the
nephrons, without increase in number.

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• Overall, these events are reiterated
throughout the growing kidney so that
older, more differentiated nephrons are
located in the inner part of the kidney
near the juxtamedullary region and
newer, less differentiated nephrons are
found at the periphery

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COLLECTING
SYSTEM
• The dichotomous branching of the ureteric bud
determines the eventual pelvicalyceal patterns
and their corresponding renal lobules .
• By 20 to 22 weeks, ureteric bud
branching is completed.
• Thereafter, collecting duct development
occurs by extension of peripheral branch
segments.
•
• The bud dilates, forming the primitive renal
pelvis, and splits into cranial and caudal
portions (the future major calyces).

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• 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.
• 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.

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• Between 22 and 24 weeks of fetal gestation the
peripheral (cortical) and central (medullary)
develops.
• Nephrogenesis completed before birth at 32-34
weeks of gestation.
• Postnatal maturation of kidney continue till 18-
24 month of age

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• Renal cortex
– 70% of total kidney volume at birth,
– becomes organized as a relatively compact,
– circumferential rim of tissue surrounding the
periphery of the kidney.
• Renal medulla
– 30% of total kidney volume at birth,
– modified cone shape with a broad base
contiguous with cortical tissue.
– The apex of the cone is formed by
convergence of collecting ducts in the inner
medulla and is termed the papilla.

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GENETI
CS
• WT1 is normally first expressed in the intermediate mesoderm
prior to kidney formation and is then expressed in the
developing kidney, gonad, and mesothelium
• The metanephrogenic mesenchyme secretes glial-
derived neurotrophic factor (GDNF) to induce and direct
the ureteric bud
• The ureteric bud secretes FGF2 and BMP7 to prevent
mesenchymal apoptosis and maintains the synthesis of
WT1
•
• Leukemia inhibitory factor (LIF) from the ureteric bud
induces the mesenchyme cells to aggregate
• Lim-1 homeodomain transcription factor causes Conversion
of the aggregated cells into a nephron

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POSITION OF
KIDNEY
• The kidney, initially in the pelvic region,
• Around 6-7th week, ascent of the kidney is
caused by diminution of body curvature and
by growth of the body in the lumbar and sacral
regions.
• 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
• During 7-8week kidney rotate 90 degree with renal
hilum changing position from ventral to

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Anomalies of
shape
• Horse shoe
kidney
• Lobulated
kidney

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Abnormal
rotation
• Nonrotation: The hilum is directed
forward.
• Incomplete rotation
• Reverse rotation: The hilum is
directed anterolaterally.

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Anomalies of
position
• The kidneys may fail to ascend. They
then lie in the sacral region.
• Incomplete ascent = lie opposite the
lower lumbar vertebrae.
• The kidneys may ascend too far, and may
even be present within the thoracic cavity.

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