DEVELOPMENT of the URINARY SYSTEM

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DEVELOPMENT of the URINARY SYSTEM Powered By Docstoc
					                      KIDNEYS
        Nick Milne School of Anatomy and Human Biology UWA
u   Ontogeny recapitulates u Readings
    Phylogeny                       u Larson “Human
                                      Embryology”
u   Early development and
                                    u Carlson “Embryology and
    evolution of the kidney           developmental biology”
    u   Intermediate mesoderm       u   McLachlan “Medical
                                        Embryology”
    u   Pronephros                  u   Sadler “Langman’s
    u   Mesonephros                     Medical embryology”
    u   Metanephros                 u   Basmajian “Grant’s
                                        Method of Anatomy
    u   Ascent and abnormalities
Ontogeny Recapitulates
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
    INTERMEDIATE MESODERM
u   Mesoderm appears in the 3
    week embryo
    u   Paraxial = somites
    u   Intermediate
    u   Lateral plate
         u   Two layers separated by the
             Coelome
u   Intermediate mesoderm
    gives rise to “Paired
    Glands” (Kidneys, Adrenals
    and Gonads)
    Pronephros
    the first kidney

u    A cavity, like the coelom
     develops inside the
     intermediate mesoderm
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
     retained.                             coelom
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.
     vertebrates
       Pronephros – in humans
u   Appears at Day 21
u   In segmented
    intermediate
    mesoderm in the
    cervical region
u   It degenerates by
    day 24
u   It is never functional
    in humans
        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
    region.
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
    mesoderm.
u   Urine is produced and drains
    along the mesonephric
    (Wolfian) duct to the
    cloaca/bladder
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
    ovary.
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
    ducts
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
    weeks.
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
     definitive kidney.
 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
Kidneys


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
                                 Anterior relations
u   Right                                       uLeft
    u   Adrenal
                                                  uAdrenal
    u   Liver
         u

         u
             bare area
             Hepatorenal pouch
                                                  uStomach

    u   Duodenum                                  uSpleen
    u   Pancreas
                                                  uPancreas
    u   Right colic
        flexure                                   uDescending
    u   Jenunum                                         Colon
                                                  uJenunum
Lecture summary

u   Early development and
    evolution
    u   Pronephros
    u   Mesonephros
    u   Metanephros
    u   Ascent and
        abnormalities
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
kidney
    uOutside  the renal
    capsule is perirenal fat
    uThen is the renal fascia
    which also surrounds the
    adrenals
    uThis is embedded in
    extraperitoneal fat
    (pararenal fat)
    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
    anterior, lower
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
renal pelvis.

				
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