Development of the urinary system

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					Development of the urinary
        system
           Dr. NEHAL MOHAMMED
                  MD, Ph.D
 Assistant professor of Anatomy &Embryology
                 KFMC-FOM
The Urinary System Throughout Life:

• Embryo develops three slightly overlapping kidney systems which
  are formed in a cranial to caudal sequence during intrauterine life in
  humans:

    – Pronephros
    – Mesonephros
    – Metanephros

        • Only metanephros persists to become the adult kidneys.
        • Metanephric kidney produces urine by the third fetal month
          which contributes to the volume of amniotic fluid.



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Development of the Pronephros:-


• At the beginning of the fourth week, the pronephros is
  represented by 7 to 10 solid cell groups in the cervical
  region. These groups form vestigial excretory units,
  nephrotomes, that regress before more caudal ones are
  formed.

•   By the end of the fourth week, all indications of the
    pronephric system have disappeared.




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Development of the Pronephros (Cont.): -




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Development of the Mesonephros:-
•   Early in the fourth week of development, during regression of the pronephric
    system, the first excretory tubules of the mesonephros appear.

•    They lengthen rapidly, form an S-shaped loop, and acquire a tuft of
    capillaries that will form a glomerulus at their medial extremity .

•   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
    show degenerative changes, and by the end of the second month the
    majority have disappeared.
Fate:-
• Ducts and tubules from the mesonephros form the conduit for sperm
  from the testes to the urethra.

• In the female, these ducts regress.


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Development of the Mesonephros (Cont.): -




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  Urogenital ridge:-




A. Relation of the genital ridge and the mesonephros showing location of the
mesonephric duct.
B. Transverse section through the mesonephros and genital ridge at the level indicated
in A.
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Fate of
Mesonephros:-




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Development of the Metanephros: -

• The metanephros, or permanent kidney, develops from two
  sources, collecting part& excretory part.

•    It forms its own excretory part or nephrons from the caudal fourth
    of the nephrogenic cord, but its collecting system originates from
    the ureteric bud.

• Ureteric bud is an outgrowth of the mesonephric duct.

• This bud gives rise to the ureter, renal pelvis, calyces, and the entire
  collecting system.

• Connection between the collecting and excretory tubule systems is
  essential for normal development

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Development of the Metanephros (Cont.):-




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Development of the collecting part of the Metanephros:-




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Development of the excretory part of the Metanephros: -


• Each newly formed collecting tubule is covered at its distal end by a
  metanephric tissue cap.

• Under the inductive influence of the tubule, cells of the tissue cap
  form small vesicles, the renal vesicles, which in turn give rise to
  small S-shaped tubules.

•     Capillaries grow into the pocket at one end of the S and differentiate
     into glomeruli.

• These tubules, together with their glomeruli, form nephrons, or
  excretory units.

• At birth the kidneys have a lobulated appearance, but the
  lobulation disappears during infancy as a result of further growth of
  the nephrons, although there is no increase in their number.
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Development of the excretory part of the Metanephros:-




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    Ascent of the kidneys: -




A to C. Ascent of the kidneys. Note the change in position between the
mesonephric and metanephric systems. The mesonephric system degenerates almost
entirely, and only a few remnants persist in close contact with the gonad. In both male
and female embryos, the gonads descend from their original level to a much lower
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position.
15   Descent of Gonads / Ascent of Kidneys
Developmental basis of adult kidney
position& vascular supply:-

          Renal artery
          Gonadal artery -
          Testes or ovaries




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Developmental anomalies of the kidney:-

•    Renal agenesis
•    Congenital polycystic kidney
•    Duplication of the ureter
•    Pelvic kidney
•    Horseshoe kidney.
•    Accessory renal arteries




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Developmental anomalies of the urinary system (Cont.): -




 A. Unilateral pelvic kidney showing the position of the adrenal gland
 on the affected side.
 B. Horseshoe kidneys showing the position of the inferior mesenteric artery.



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Developmental anomalies of the urinary system (Cont.): -




 A&B. complete and a partial double ureter.
 C.   Possible sites of ectopic ureteral openings in the vagina, urethra,
 and vestibule.
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Divisions of the cloaca: -
•During the fourth to seventh weeks of development the cloaca divides by the urorectal
septum into the urogenital sinus anteriorly and the anal canal posteriorly.




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   Development of the urinary bladder: -
•The upper and largest part of the urogenital sinus is the urinary bladder.
•Initially the bladder is continuous with the allantois, but when the lumen of the allantois is
obliterated, a thick fibrous cord, the urachus, remains and connects
the apex of the bladder with the umbilicus .In the adult, it is known as the median umbilical
ligament.




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   Development of the urinary bladder (Cont.):-
•During differentiation of the cloaca, the caudal portions of the mesonephric ducts are absorbed
into the wall of the urinary bladder .Consequently, the ureters (initially outgrowths from the
mesonephric ducts), enter the bladder separately .
• As a result of ascent of the kidneys, the orifices of the ureters move farther cranially.
•Since both the mesonephric ducts and ureters originate in the mesoderm, the mucosa of the
bladder formed by incorporation of the ducts (the trigone of the bladder) is also mesodermal.




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Fig. 26.22




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Developmental anomalies of the urinary bladder:-


•    urachal fistula.
•    urachal cyst.
•    urachal sinus.
•    Exstrophy of the bladder.
•    Exstrophy of the cloaca.




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Developmental anomalies of the urinary system (Cont.): -




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