EMBRYOLOGY AND ANATOMY OF KIDNEY

EMBRYOLOGY AND ANATOMY OF
KIDNEY
Dept of Urology
Govt Royapettah Hospital and Kilpauk Medical College
Chennai
1

Moderators:
Professors:
• Prof. Dr. G. Sivasankar, M.S., M.Ch.,
• Prof. Dr. A. Senthilvel, M.S., M.Ch.,
Asst Professors:
• Dr. J. Sivabalan, M.S., M.Ch.,
• Dr. R. Bhargavi, M.S., M.Ch.,
• Dr. S. Raju, M.S., M.Ch.,
• Dr. K. Muthurathinam, M.S., M.Ch.,
• Dr. D. Tamilselvan, M.S., M.Ch.,
• Dr. K. Senthilkumar, M.S., M.Ch.
Dept of Urology, GRH and KMC, Chennai. 2

EMBRYOLOGY OF KIDNEY
3
Dept of Urology, GRH and KMC, Chennai.

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)
4

PRONEPHROS
• 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
5

MESONEPHROS
• 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 glomerulus
6

7

• 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 simultaneously
8

– 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.
9

10

11

METANEPHROS
• 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
12

• 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
13

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.
• The proximal end of each nephron forms Bowman’s capsule.
14

• The distal end forms an open connection with one of the collecting
tubules, establishing a passageway from Bowman’s capsule to 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.
15

16

17

• 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
18

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).
19

• 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.
20

21

22

• 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
23

• 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.
24

GENETICS
• 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
• Hoxa-13 and Hoxd-13 act on urogenital deferentiation
25

26

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 anteromedially
27

Anomalies of shape
• Horse shoe kidney
• Pancake kidney
• Lobulated kidney
28

Abnormal rotation
• Nonrotation: The hilum is directed forward.
• Incomplete rotation
• Reverse rotation: The hilum is directed
anterolaterally.
29

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.
30

31

ANATOMY OF KIDNEY
• Paired ovoid, reddish-brown retroperitoneal organs
situated in the posterior part of the abdomen on each side
of the vertebral coloumn
• Lie on the psoas muscles; thus the longitudinal axes of the
kidneys are oblique .
• The upper poles more medial and posterior than the
inferior poles.
• The medial aspect of each kidney is rotated anteriorly at an
angle of approximately 30 degrees.
32

33

• The exact position of the kidney within the
retroperitoneum varies:
➢The kidneys move inferiorly approximately 3
cm (one vertebral body) during inspiration and
during changing body position from supine to
the erect.
34

DIMENSIONS
• Length- 10 to 12 cm
• Width- 5.0 to 7.5 cm
• Thickness- 2.5 to 3.0 cm.
➢Weight of kidney = approx. 125-170 gm. ( 10-
15 gm lighter in females)
➢Relatively larger in children and have
prominent fetal lobulations.
35

Right kidney vs left kidney
Right kidney
• Reside between the top
of the 1st lumbar
vertebra to the bottom of
the 3rd lumbar vertebra.
• The right kidney is
slightly shorter and wider
because of downward
compression by the liver.
• The right kidney is
related to the 12th rib,
Left kidney
• Between the 12th
thoracic vertebra and the
3rd lumbar vertebra.
• Dromedary hump more
common on left side.
• Left kidney is related to
the 11th and 12th ribs
36

RELATIONS
• Surfaces of kidney are - anterior and
posterior.
• Borders are - medial and lateral.
• Poles of kidney are – superior and inferior.
• Anteriorly kidney is related - abdominal
viscera
Posteriorly - osteomuscular area
37

ANTERIOR RELATIONS
RIGHT KIDNEY
• right adrenal gland
• liver,
• second part of duodenum,
• ascending colon,
• hepatic flexure of colon.
LEFT KIDNEY
• Left adrenal,
• Pancreas,
• splenic vessels,
• Stomach,
• Spleen,
• Dj flexure,
• Ligament of trietz,
• Descending colon,
• Splenic flexure of colon,
• Loops of jejunum.
38

39

RIGHT LEFT
40

POSTERIOR RELATIONS OF KIDNEY
LEFT KIDNEY
• Projection of 11th rib
• Area for diaphragm
• Area for aponeurosis of
transversus abdominis
muscle
• Area for quadratus
lumborum muscle
• Area for psoas major muscle
RIGHT KIDNEY
• Area for diaphragm
• Area for aponeurosis of
transversus abdominis
muscle
• Area for quadratus
lumborum muscle
• Area for psoas major muscle
41

LEFT RIGHT
42

43

APPLIED ANATOMY
• Posterior reflection of the pleura extends
inferiorly to the 12th rib
• Lung edge lies above the 11th rib (at the 10th
intercostal space)
• Risk of injury to the lung from a 10th
intercostal percutaneous approach to the
kidney
44

Relationship to ribs and pleura
45

MEDIALBORDER
» In medial border of each kidney there is a vertical fissure
called renal hilum/porta
• Renal vessels, nerves, lymphatics, enter and exit through
through hilum
• Concavity of hilum is continous with deep declivity in
medial border of kidney called renal sinus
• Within renal sinus is renal pelvis, a funnel shaped sac
formed by widely expanded portion of proximal ureter and
by junction of major calices
46

• Intra renal pelvis denotes the pelvis that is
almost covered by renal parenchyma.
• Renal pelvis almost bifurcates or trifurcates
within the sinus producing 2/3 major calyx.
• Each major calyx again divide into 5-14 minor
calyxes receiving collecting ducts ( 500).
• Renal pelvis commonly lies posterior to renal
vessels.
• Has a capacity of 3 to 10 ml of urine.
47

• LATERAL BORDER :
Related to perirenal fascia, gerota’s fascia,
para renal fascia.
48

GEROTA’S FASCIA
• Encloses the kidney & perirenal fat and
adrenals.
• Anatomic barrier to spread of malignancy
• Superiorly and laterally it is closed
• Medially it crosses the midline to fuse with
the fellow of opp. Side
• Inferiorly it remains open- perinephric fluid
can track into pelvis
49

RENAL FASCIA
50

• Two distinct regions :-
Cortex - pale outer region,
Medulla - darker inner region
• Renal medulla - 8 to 18 striated, distinct, conically shaped areas
called renal pyramids.
• The apex of the pyramids forms the renal papilla, and each papilla is
cupped by an individual minor calyx.
• The base of the pyramids is positioned at the corticomedullary
boundary.
• Renal cortex is approximately 1 cm in thickness and covers the base
of each renal pyramid peripherally and extends downward between
the individual pyramids to form the columns of Bertin . 51

• Interlobar arteries traverse these columns of
Bertin
• Therefore percutaneous access to the collecting
system is usually performed through a renal
pyramid into a calyx to avoid these columns of
Bertin containing larger blood vessels
• The functional unit of the kidney is the nephron.
Approximately 0.4 to 1.2 million nephrons are
found in each adult kidney.
52

• The cortex made up of the glomeruli with PCT &
DCT.
• The renal pyramids are made up of loops of
Henle and collecting ducts.
• Ducts join to form the papillary ducts (about 20),
which open at the papillary surface (area cribosa)
and drain urine into the collecting system(into
the fornix of a minor calyx).
53

54

MINOR CALYX
• The renal papillae drain into the minor calyces,
(the most peripheral portions of the intrarenal
collecting system).
• Range in number from 5 to 14 (mean- 8)
• Simple (drains one papilla)
• Compound (drains two or three papillae)
• Compound calyces are the rule in the upper
calyceal group, are common in the lower calyceal
group, and are rare in the middle calyceal group
55

• Three calyceal groups: upper, middle, and lower.
• Minor calyces, either directly or after coalescing into
major calyces, drain by infundibula into the renal pelvis
• Compound calyces of the poles of the kidney are
oriented facing their respective poles.
• Simple calyces usually come in pairs, with one facing
anteriorly and one facing posteriorly
56

57

• Drainage of the upper pole into the renal pelvis is by a
single midline infundibulum in the majority of kidneys.
• Drainage from the lower pole is via a single infundibulum
in about half of human kidneys.
• The middle calyces are typically arranged in a series of
paired anterior and posterior calyces.
• In about two thirds of kidneys, there are two major calyceal
systems—an upper one and lower one—and the middle
calyces drain into either or both systems
58

CLASSIFICATION OF THE
PELVIOCALYCEAL SYSTEM
Group A (62.2%)
• Two major calyceal groups (superior and inferior)
• Midzone calyceal drainage dependent on these two
major groups
➢ Type A-I (45%). The kidney midzone is drained by minor
calyces that are dependent on the superior and/ or
inferior calyceal groups
➢ Type A-II (17.2%). The kidney midzone is drained
simultaneously by crossed calyces, one draining into
the superior calyceal group and the other draining into
the inferior calyceal group 59

60

Group B (37.8%)
• Midzone (hilar) calyceal drainage independent of both
the superior and inferior calyceal groups
• Type B-I (21.4%). The kidney midzone is drained by a
major calyceal group, independent of both the superior
and the inferior groups.
• Type B-II (16.4%). The kidney midzone is drained
by minor calyces (one to four) entering directly into the
renal pelvis .
61

62

ORIENTATION OF CALYCES
• Important consideration for percutaneous surgery-
anteroposterior orientation of the calyces,
• Because access (from the typical posterior or
posterolateral approach) into a posterior calyx allows
relatively straight entry into the rest of the kidney,
whereas
• Percutaneous puncture of an anterior calyx requires
an acute angulation to enter the renal pelvis, which
may not be possible with rigid instrumentation .
63

ORIENTATION OF CALYCES
• Paired anterior and posterior calyces usually
enter at about 90 degrees from each other.
• The relative mediolateral orientation (on
anteroposterior radiography) is determined by
the relationship of this 90-degree unit to the
frontal plane of the kidney.
64

BRODEL TYPE
• Unit is rotated anteriorly, such that the posterior
calyces are about 20 degrees behind the frontal plane
• Anterior calyces are 70 degrees in front of the frontal
plane
• The posterior calyces are lateral, and the anterior
calyces are medial in this case
• Most right kidneys have a Brodel-type orientation
(posterior calyces are lateral)
65

HODSON TYPE
• Calyceal pairs are rotated posteriorly, with the
posterior calyces 70 degrees behind the
frontal plane and appearing medial
• Anterior calyces 20 degrees in front of the
frontal plane and appearing lateral
• Left kidneys have a Hodson-type orientation
(posterior calyces are medial)
66

67

• Mostly calyces of the upper pole are suitable
for percutaneous access from posterior
approach, whereas care must be taken to
select a posterior minor calyx in middle and
lower groups.
• Safest place to access collecting system is
directly into calyceal fornix as it will avoid
interlobar arteries and arcuate arteries…
68

FOR PERCUTANEOUS ACCESS
▪ In prone position, prefered calyx are posterior ones.
▪ Should never be directed into infundibulum or renal
pelvis.
▪ Upper pole calyx is most versatile site through which to
enter the upper urinary tract collecting system.
▪ Subcostal approach is safest route to kidney.
69

RENAL VASCULATURE
• The renal arteries arise from the aorta at the level of the intervertebral disk
between the L1 and L2 vertebrae.
• Each artery divides into five segmental end arteries that do not anastomose
significantly with other segmental arteries.
• The renal artery usually divides to form anterior and posterior divisions.
• The anterior division supplies anterior two thirds of the kidney, and the posterior
division supplies the posterior one third of the kidney.
• Typically, the anterior division divides into four anterior segmental branches:
apical, upper, middle, and lower.
• The posterior segmental artery - first and most constant branch, which separates
from the renal artery before it enters the renal hilum
70

SEGMENTAL BRANCHES
• End arteries- so injury lead to segmental infarction.
• First and most constant branch POSTERIOR SEGMENTAL
BRANCH
• Four anterior branches
• APICAL
• UPPER
• MIDDLE
• LOWER
• Posterior segmental artery passes posterior to renal pelvis,
• SURGICAL IMPORTANCE - when it passes anterior to pelvis
lead to puj obstruction..
71

72

73

• In the renal sinus, the segmental arteries branch into lobar arteries,
which further subdivide in the parenchyma to form interlobar
arteries.
• The interlobar arteries progress peripherally within the cortical
columns of Bertin, avoiding the renal pyramids but in a close
association with the minor calyceal infundibula.
• At the base (peripheral edge) of the renal pyramids, the interlobar
arteries branch into arcuate arteries.
• Instead of moving peripherally, the arcuate arteries parallel the
edge of the corticomedullary junction and move radially, where
they eventually divide to form the afferent arteries to the
glomerulus.
74

75

76

ANOMALIES OF RENAL ARTERY
• Multiple renal arteries- kidney supplied by more than
one artery..MC on left side.
• Accessory renal artery – 2 or more branch supply the
same renal segment. MC on left side 30 to 35%
• They enter either in upper pole/ lower pole of kidney.
• Such accessory artery can cause ureteric obstruction
lead to secondary HUN..
• But ligation of accessory renal artery result in a portion
of infarction
• Arterial anomalies are more common on left and
venous anomalies are more common on right.
77

COMMON ANATOMIC VARIANTS OF
VESSEL
• Occurs in 25- 40%
• M.C is supernumery arteries- More commen
on Left side.
• Lower pole arteries can cross ant to collection
system and cause PUJ obstruction
78

RENAL VEIN
• The vein is located directly anterior to the
renal artery.
• This position can vary up to 1-2 cm cranially or
caudally relative to the artery
79

LEFT RENAL VEIN
• The left renal vein - 6 to 10 cm in length and
drains into IVC after passing posterior to the
superior mesenteric artery and anterior to the
aorta
• Left renal vein enters the IVC at a slightly more
cranial level and a more anterolateral location
• The left renal vein receives the left adrenal
vein superiorly, lumbar vein posteriorly, and
left gonadal vein inferiorly
80

RIGHT RENAL VEIN
• The right renal vein is generally 2 to 4 cm in
length and enters the right lateral to
posterolateral edge of the IVC
• Right renal vein enters the IVC at a slightly
more caudal level.
• The right renal vein typically do not receive
any branches
81

• Unlike the arterial supply, the venous drainage
communicates freely through “Venous
Collars” around the infundibula,
• Extensive collateral circulation is present in
the venous drainage of the kidney.
• Surgically, this is important, because unlike the
arterial supply, occlusion of a segmental
venous branch has little effect on venous
outflow
82

83

84

BRODEL’S LINE /AVASCULAR PLANE
• Slightly behind the convex border at the
posterior half of kidney (approximately 2/3 rd
way from lateral border ).
• Incision in this area will permit to remove
stone within renal calices with minimal
damage.
85

86

LYMPHATICS
• Largely follow blood vessels through the column
of bertin.
• Lymphatics empty to LN near renal hilum
• L KIDNEY:-
-Lt lateral para- aortic LN
• R KIDNEY:-
-Rt inter aortocaval and Rt lateral para
caval LN and anterior and posterior inferior
venacaval nodes.
87

LYMPHATICS OF RIGHT KIDNEY
88

LYMPHATICS OF LEFT KIDNEY
89

NERVE SUPPLY
• SYMPATHETIC - From T8 to L1 through celiac
and aortico renal ganglion
- Vasoconstriction
• PARA SYMPATHETIC- From vagus
- vasodilatation
➢Remember that kidney can function well even
without neurological control
90

APPLIED ANATOMY
• Avoid injury to T11 and T12 nerves – to avoid
post op paraesthesias and postop muscle
bulding from partial muscle paralysis.
• While suturing ensure not to entrap the lower
costal nerves.
• Injury to 12 th nerve lead to gluteal
paraesthesias.
91

RADIOLOGICAL ANATOMY OF RENAL
PARENCHYMA
• On USG- In adults normal kidneys have smooth margins
and isoechoic to liver
• Both renal cortices and pyramids are usually hypoechoic
to the liver, spleen, and renal sinus. Compared with renal
parenchyma, the renal sinus appears hyperechoic
because of the presence of hilar adipose tissue, blood
vessels, and lymphatics.
• The renal cortices of newborn kidneys are isoechoic or
hyperechoic to the liver and splenic parenchyma
• Echogenicity correlates to the severity of pathologic changes
in renal parenchyma.
92

ON CT
• On unenhanced computed tomography (CT), the renal
parenchyma is homogeneous, with a density ranging
from 30 to 60 (HU)
• After intravenous contrast injection = 80-120HU.
• Arterial phase= after 20 to 30 seconds of contrast
• The corticomedullary= 30-70 sec ( cortex brighter)
• The nephrographic CT phase= 80 to 120 seconds,
equally enhances renal cortex and medulla and is
considered to be the optimal phase for detection of
renal neoplasms.
• The excretory ct phase= more than 3 minutes after
contrast
93

ON MRI
• MRI= T1-weighted sequences show the renal
cortex much brighter than the renal medulla,
whereas the cortex is slightly less intense than
the medulla on T2-weighted sequences
• Pelvis containing fat appears hypertense on
both T1 and T2
• Nephrogenic phase= 60-90 sec
• Excretory phase= 120 sec
94

THANKS
95

EMBRYOLOGY AND ANATOMY OF KIDNEY

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