Editing Pediatrics: Anomalies of the Kidneys (section)

== Renal Embryology ==

* '''Embryonic kidneys in order of their appearance:'''
*# '''Pronephros'''
*#* Develops late in the 3rd week, and it '''completely regresses''' by the start of the 5th week
*# '''Mesonephros'''
*#* '''Regresses partially by the 4th month'''
*#** '''In males, the mesonephric tubules become the efferent ductules that serve as a link between the testicle and the mesonephric/Wolffian duct (WD) structures''' (the body and tail of the epididymis and vas deferens)
*# '''Metanephros'''
*#* '''Becomes the permanent kidney.'''
** All 3 develop from the intermediate mesoderm.
*** '''The definitive kidney differentiates from the metanephric blastema''', which is a specialized region of the intermediate mesoderm termed the metanephric mesenchyme
**** '''This process requires the reciprocal induction between the metanephric blastema and the ureteral bud'''
***** '''The metanephric blastema sends signals to the WD to initiate ureteric bud formation from its caudal end between 5-7 weeks’ gestation.'''
***** The ureteric bud evaginates and invades the metanephric blastema and branches repeatedly in a characteristic pattern to form the collecting duct system. The ureteral tips induce nephron differentiation in the adjacent mesenchyme, forming the mature metanephros
**** Although renal maturation continues to take place postnatally, '''nephrogenesis is essentially complete before birth at around 32-34 weeks’ gestation''' (CW11 p2826 "nephrogenesis is completed before birth at around 32 to 34 weeks of gestation"; CW12 p341 "By 34 to 36 weeks’ gestation, nephrogenesis is complete")
** The full term neonate has a glomerular filtration rate (GFR) of only 2 ml/minute.§
*** When this is normalized for body surface area of an adult, the GFR of a full term neonate is approximately 20 ml/min/1.73 m2
*** In an adult, GFR normally 100–120 ml/min/1.73 m2 (an average adult body surface area).