Anatomy 12: Embryology of the Urinary
System
# of kidneys during development
3 pairs of kidneys develop from intermediate mesoderm (IM) cephalocaudally starting at wk
4
-1. pronephros in cervical region = non-fxn => complete degenerates
-2. mesonephros in thoracic/upper lumbar region = produces fetal urine but degenerates
-3. metanephros in sacral region = persists as definitive adult kidneys
pronephros
-derived from intermediate mesoderm (IM)
-IM cells begin to cluster => nephrotomes in cervical region at beginning of wk 4
-non-fxn kidney that degenerates by end of wk 4
mesonephros
-derived from intermediate mesoderm (IM)
-IM cells begin to cluster => nephrotomes in thoracic/upper lumbar region at end of wk 4
-forms nephrons that produce fetal urine during wks 6-10
-eventually degenerates forming....
-Wolffian (mesonephric) ducts in males = connects mesonephros to cloaca (future bladder)
-becomes vas deferens
-epoophoron in females
-will become trigone of bladder in males and females
metanephros
-derived from intermediate mesoderm (IM)
-IM cells begin to cluster => nephrotomes in sacral region where mesonephric duct
(Wolffian) meets cloaca during wk 5
-forms metanephric blastema
, -ureteric bud arises from mesonephric duct (Wolffian) growing towards metanephric
blastema => developing kidney
-ureteric bud then gives rise to...
-ureter (emptying into bladder, now cloaca)
-renal pelvis
-major/minor calyces
-collecting duct/tubules
-definitive kidney begins to fxn ~12 wks
nephron formation
-metanephric blastema (recall intermediate mesoderm from metanephros) gives off
metanephric blastema cap
-cap becomes canalized => nephric vesicle
-ureteric bud (recall outgrowth from mesonephric duct) grows towards nephric vesicle
-fusion of the 2 => nephron w/ regions derived from both parts
-metanephric blastema => glomerulus/Bowman's to DCT (including loop of Henle)
-ureteric bud => collecting tubule/duct to ureter (including calyces and renal pelvis)
(see broken line in pic)
characteristics of infantile kidneys
-small/lobulated
-due to small size of nephrons
-individual nephrons continue to grow => lobulations eventually disappear
ascent of kidneys through development
-inc growth of sacral/lumbar regions => lengthened caudal end of embryonic body
-results in relative upward movement of kidneys
-during ascent kidneys rotate ~90*
-originally hilum faces anteriorly but ends up medial (slightly anterior)
blood supply of kidneys through ascent
-kidneys originally fed by branches from common iliac aa. while in sacral region
-as they ascend they send out new branches superiorly and lose old caudal branches
System
# of kidneys during development
3 pairs of kidneys develop from intermediate mesoderm (IM) cephalocaudally starting at wk
4
-1. pronephros in cervical region = non-fxn => complete degenerates
-2. mesonephros in thoracic/upper lumbar region = produces fetal urine but degenerates
-3. metanephros in sacral region = persists as definitive adult kidneys
pronephros
-derived from intermediate mesoderm (IM)
-IM cells begin to cluster => nephrotomes in cervical region at beginning of wk 4
-non-fxn kidney that degenerates by end of wk 4
mesonephros
-derived from intermediate mesoderm (IM)
-IM cells begin to cluster => nephrotomes in thoracic/upper lumbar region at end of wk 4
-forms nephrons that produce fetal urine during wks 6-10
-eventually degenerates forming....
-Wolffian (mesonephric) ducts in males = connects mesonephros to cloaca (future bladder)
-becomes vas deferens
-epoophoron in females
-will become trigone of bladder in males and females
metanephros
-derived from intermediate mesoderm (IM)
-IM cells begin to cluster => nephrotomes in sacral region where mesonephric duct
(Wolffian) meets cloaca during wk 5
-forms metanephric blastema
, -ureteric bud arises from mesonephric duct (Wolffian) growing towards metanephric
blastema => developing kidney
-ureteric bud then gives rise to...
-ureter (emptying into bladder, now cloaca)
-renal pelvis
-major/minor calyces
-collecting duct/tubules
-definitive kidney begins to fxn ~12 wks
nephron formation
-metanephric blastema (recall intermediate mesoderm from metanephros) gives off
metanephric blastema cap
-cap becomes canalized => nephric vesicle
-ureteric bud (recall outgrowth from mesonephric duct) grows towards nephric vesicle
-fusion of the 2 => nephron w/ regions derived from both parts
-metanephric blastema => glomerulus/Bowman's to DCT (including loop of Henle)
-ureteric bud => collecting tubule/duct to ureter (including calyces and renal pelvis)
(see broken line in pic)
characteristics of infantile kidneys
-small/lobulated
-due to small size of nephrons
-individual nephrons continue to grow => lobulations eventually disappear
ascent of kidneys through development
-inc growth of sacral/lumbar regions => lengthened caudal end of embryonic body
-results in relative upward movement of kidneys
-during ascent kidneys rotate ~90*
-originally hilum faces anteriorly but ends up medial (slightly anterior)
blood supply of kidneys through ascent
-kidneys originally fed by branches from common iliac aa. while in sacral region
-as they ascend they send out new branches superiorly and lose old caudal branches
