Nick Milne School of Anatomy and Human Biology UWA
u Ontogeny recapitulates u Readings
Phylogeny u Larson “Human
u Early development and
u Carlson “Embryology and
evolution of the kidney developmental biology”
u Intermediate mesoderm u McLachlan “Medical
u Pronephros u Sadler “Langman’s
u Mesonephros Medical embryology”
u Metanephros u Basmajian “Grant’s
Method of Anatomy
u Ascent and abnormalities
Phylogeny Ernst Haeckel 1860?
u Ontogeny is the development of the individual
u Phylogeny is the evolution of the species
u So this is the idea that during development an
organism (or an organ) goes through the same
stages as during their evolution.
u Consider the Frog
u It development retraces the evolution of vertebrates
from fish to reptiles
u From the tadpole stage This idea should be
u Water breathing with tail and no limbs (like a fish) considered as a “Parable”
u Rudimentary limbs
u Reduction of tail It is not necessarily true
u Development of lungs – breathes air but it is a useful idea.
u Fully developed limbs, loss of tail moves onto land
u To the fully developed frog
u Mesoderm appears in the 3
u Paraxial = somites
u Lateral plate
u Two layers separated by the
u Intermediate mesoderm
gives rise to “Paired
Glands” (Kidneys, Adrenals
the first kidney
u A cavity, like the coelom
develops inside the
u Balls of bloods vessels from
the aorta bulge into the space
– The Glomerulus.
u The glomerulus allows excess
water to leave the blood while
salts and macromolecules are u Initially the water filters into the
u This kind of kidney is found u Later, part of the cavity inside the
in primitive fish (eg Lampreys) intermediate mesoderm links up
with similar parts in adjacent
and in the embryos of most segments to form a duct.
Pronephros – in humans
u Appears at Day 21
u In segmented
mesoderm in the
u It degenerates by
u It is never functional
Mesonephros – middle kidney
u When some primitive fish returned
to the sea they had the reverse
osmotic problem, water tended to
diffuse out of their blood.
u They developed the mesonephric
kidney located in the thoracic
u The mesonephros had a smaller
glomerulus but a larger system of
tubules so that the filtration part
was reduced and the reabsorbing uMany bony fish and some amphibians
part was increased. have a mesonephric kidney.
u This was an important preadaption uThe tubules all connect with the
to life on the land where drying out mesonephric (Wolfian) duct.
is a constant problem.
Mesonephros - in humans
u The Mesonephros first appears
early in week 4
u In thoracic and lumbar
segments of intermediate
u Urine is produced and drains
along the mesonephric
(Wolfian) duct to the
u In week 5 the thoracic
segments regress but the
mesonephric kidney continues
functioning until week 10
Fate of the Mesonephric (Wolfian) ducts
u The development of the metanephric
kidney accompanied the changes in
the reproductive system.
u The gonads of primitive vertebrates
release their eggs and sperm into the
coelom, from there they pass via small
pores into the cloaca.
u In higher vertebrates the eggs are still
released into the coelom, but the
cloacal pores have become specialised
tubes which open adjacent to the
u In the embryo, this egg collecting tube
(paramesonephric duct) lies parallel to
the mesonephric duct.
Male and Female genital ducts
u Initially both sexes have both mesonephric and paramesonephric
u In females
u Eggs are still released into the coelom (peritoneal cavity) but are gathered up in
the uterine tubes.
u The two paramesonephric ducts become the uterine tubes.
u Distally the paramesonephric ducts fuse together to form the uterus and vagina.
u The mesonephric duct degenerates completely.
u In higher vertebrates sperm is never released into the coelom but
reaches the outside by passing through some derivative of the urinary
system. In birds, reptiles and mammals the testis develops a
connection with the mesonephric duct (at the time that the mesonephros is degenerating).
u In males
u The mesonephric duct becomes the ductus deferens, seminal vesicle and parts of
the prostate gland.
u The paramesonephric duct degenerates completely.
Metanephros – definitive kidney
u The metanephros or definitive
kidney of higher vertebrates,
begins when the metanephric
ducts (ureteric buds) sprout
from the distal end of the
mesonephric duct at about 5
u The ureteric buds induce
intermediate mesoderm in the
sacral region to form a
metanephric blastema which
forms the glomeruli and
tubules of the nephrons.
Evolution of the Kidneys: Metanephros
u The ureteric buds bifurcate again and again to
form the calyces and collecting duct system of the
u The kidneys begin producing urine by week 12,
and it adds to the volume of the amniotic fluid.
The fetus drinks this fluid in utero.
u The fetal kidneys are not responsible for
excretion as the placenta serves this function
Ascent of the
u In the 6th week the kidneys begin to ascend from the sacral region to
their position in the upper abdomen.
u The metanephric ducts elongate and become the ureters.
u As the kidney ascends it receives new segmental arteries from the aorta
and loses those vessels below (“climbing a ladder”). Thus sometimes
there is more than one renal artery.
u Sometimes one kidney fails to ascend => pelvic kidney
u Sometimes the left and right kidneys become attached in the pelvis then
the horseshoe kidney can’t ascend above the inferior mesenteric artery
Position of kidneys
u Kidneys lie on the psoas muscle beside
the vertebral bodies.
u The diaphragm and 11th and 12th ribs lie
behind the upper half of each kidney.
u Therefore they move with breathing
u Left is higher than right (liver)
u Upper poles T12
u Hilum is at L1/2
u Lower poles at L3
u Upper poles are more medial (psoas).
u In the hilum:
u Renal vein is the most anterior.
u Followed by renal artery & pelvis/ureter It crosses the aorta
Is crossed by the SMA
u Note that the left renal vein is longer . Receives left gonadal vein
u Right uLeft
u Duodenum uSpleen
u Right colic
u Jenunum Colon
u Early development and
u Ascent and
u Position and relations
u Lobes and segments
Orientation and surroundings
u The medial border of each kidney is anterior to the lateral border
(psoas). Thus the coronal plane of the kidney is at 30 degrees to
the coronal plane of the body.
uLayers surrounding the
uOutside the renal
capsule is perirenal fat
uThen is the renal fascia
which also surrounds the
uThis is embedded in
Renal Lobes and their papillae/calyces
u There are 14 lobes originally
u Each lobe corresponds with a renal pyramid
(plus its cap of cortex), and empties via its
papilla, into a minor calyx
u Lobes fuse so that there are between 14 and 6,
usually 8 (26%)
u Most fusion happens at the upper and lower
poles so that those papillae are compound.
u Simple papillae have valve-like slits where the
ducts open – Non-refluxing
u Compound papillae allow reflux
u Vescicouretal reflux occurs in children and if
the urine can enter the parenchyma of the
kidney it causes infection and damage
5 Segments of the Kidney
u Each segment is the area supplied one branch of the renal artery. (end arteries)
u The front of the kidneys has four segments: apical, upper anterior, middle
u The back of the kidney has the posterior segment and the posterior aspects
of the apical and lower.
u Easy way to remember: like your hand holding a glass four fingers in front
and the thumb behind.
uThe posterior branch of the
artery branches off first and
passes over the renal pelvis to
reach the posterior aspect. The
four anterior branches continue in
the plane between the vein and