Urinary system development

Embryology Course, Second year, Faculty of Medicine, Damascus University

1. Urinary System Development
www.marwanalhalabi.com
Marwan Alhalabi
Professor of Reproductive Medicine and Infertility,
Damascus University
Head of Assisted Reproduction Unit, Orient Hospital
President of Middle East Fertility Society
Past President of Syrian Society of Obstetricians and Gynecologists

2. The Urogenital System

3. Development of Urinary System
The Urinary System
Urinary
Bladder
Ureters
and
Urethra
Kidneys

5. Intermediate Mesoderm
The midline NOTOCHORD secretes factors that organize the dorsal-
ventral and medio-lateral axes of the embryo.

6. Functionally the urogenital system can be divided into two entirely
different components:
1.Theurinary system
2.The genital system.
qEmbryologicallyand anatomicallythey are intimately
interwoven.
qBoth develop from a common mesodermal ridge (intermediate
mesoderm) along the posterior wall of the abdominal cavity,
qInitially the excretory ducts of both systems enter a common
cavity, the cloaca.
Development of Urinary System

7. Formation of The Nephrogenic Cord

8. •Three slightly overlapping kidney systems are formed in a cranial
to caudal sequence during intrauterine life in humans:
1.The pronephros, (rudimentary and nonfunctional).
2.The mesonephros, (function for a short time during the early fetal
period).
3.The metanephros, (forms the permanent kidney)
Urinary System (KIDNEY SYSTEMS)

9. Urinary System Development

10. •Atthebeginningofthefourthweek,thepronephrosis
representedby7to10solidcellgroupsinthecervical
region.
•Thesegroupsformvestigialexcretoryunits,nephrotomes,
thatregressbeforemorecaudalonesareformed.
•Bytheendofthefourthweek,allindicationsofthe
pronephricsystemhavedisappeared.
Pronephros

11. Mesonephros

12. Mesonephros

13. •Themesonephrosandmesonephricductsarederivedfrom
intermediatemesodermfromupperthoracictoupper
lumbar(L3)segments.
•Earlyinthefourthweek,thefirstexcretorytubulesofthe
mesonephrosappear.
Mesonephros

14. •Theylengthenrapidly,formanS-shapedloop,andacquireatuftof
capillariesthatwillformaglomerulusattheirmedialextremity.
•AroundtheglomerulusthetubulesformBowman’scapsule,and
togetherthesestructuresconstitutearenalcorpuscle.
•Laterallythetubuleentersthelongitudinalcollectingductknown
asthemesonephricorwolffianduct.
Mesonephros

19. •Sincethedevelopinggonadisonitsmedialside,theridgeformedbyboth
organsisknownastheurogenitalridge.
•Thecaudaltubulesarestilldifferentiating,
•Thecranialtubulesandglomerulishowdegenerativechanges,andbythe
endofthesecondmonththemajorityhavedisappeared.
•Inthemaleafewofthecaudaltubulesandthemesonephricduct
persistandparticipateinformationofthegenitalsystem,butthey
disappearinthefemale.
Mesonephros

21. Mesonephros

22. Mesonephros

23. Mesonephros

24. Mesonephros

25. Mesonephros

26. •Thethirdurinaryorgan,themetanephros,orpermanentkidney,
appearsinthefifthweek.
•Itsexcretoryunitsdevelopfrommetanephricmesoderminthesame
mannerasinthemesonephricsystem.
•Thedevelopmentoftheductsystemdiffersfromthatoftheother
kidneysystems.
Metanephros: The Definitive Kidney

27. Metanephros

28. Nephrons

29. Nephrons

30. •Collecting ducts of the permanent kidney develop from the
ureteric bud.
•The bud penetrates the metanephric tissue.
•The bud dilates, forming the primitive renal pelvis, and splits into
cranial and caudal portions (the future major calyces).
Collecting System

31. •Each calyx forms two new buds while penetrating the metanephric
tissue.
•These buds continue to subdivide until 12 or more generationsof
tubules have formed.
•Meanwhile, at the periphery more tubules form until the end of
the fifth month.
Collecting System

32. Relation of the
hindgut and
cloaca at the end
of the 5thweek.
The ureteric bud penetrates the metanephric mesoderm (blastema).
Metanephros

34. •The tubules of the second order enlarge and absorb those of
the third and fourth generations, forming the minor calyces
of the renal pelvis.
•Collecting tubules of the fifth and successive generations form
the renal pyramid.
•The ureteric bud gives rise to the;
•ureter,
•renal pelvis,
•major and minor calyces,
•1 million to 3 million collecting tubules.
Collecting System

35. Nephrons

40. Metanephros

41. Metanephros

42. Metanephros

43. •Eachnewlyformedcollectingtubuleiscoveredatitsdistal
endbyametanephrictissuecap.
•Cellsofthetissuecapformsmallvesicles,therenalvesicles,
•RenalvesiclesgiverisetosmallS-shapedtubules.
•CapillariesgrowintothepocketatoneendoftheSand
differentiateintoglomeruli.
Excretory System

44. •TheproximalendofeachnephronformsBowman’scapsule.
•Thedistalendformsanopenconnectionwithoneofthecollecting
tubules,establishingapassagewayfromBowman’scapsuletothe
collectingunit.Continuouslengtheningoftheexcretorytubuleresults
informationoftheproximalconvolutedtubule,loopofHenle,and
distalconvolutedtubule.
Excretory System

45. •The kidney develops from two sources:
•(a) metanephric mesoderm, which provides excretory units.
•(b) the ureteric bud, which gives rise to the collecting system.
•Nephrons are formed until birth, at which time there are approximately 1 million in each kidney.
•Urine production begins early in gestation, soon after differentiation of the glomerular capillaries, which start to form by
the 10th week.
•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
Excretory System

47. •Thekidney,initiallyinthepelvicregion,
•latershiftstoamorecranialpositionintheabdomen.
•Thisascentofthekidneyiscausedbydiminutionofbodycurvature
andbygrowthofthebodyinthelumbarandsacralregions.
•Duringitsascenttotheabdominallevel,itisvascularizedbyarteries
thatoriginatefromtheaortaatcontinuouslyhigherlevels.
•Thelowervesselsusuallydegenerate,butsomemayremain.
Position of The Kidney

48. Relocation of The Kidney

49. Definitive Metanephros

50. Relocation of The
Kidney

51. Ascent of the kidneys: Gonad descent

52. Ascent of the kidneys: Gonad descent

53. Changes of developing kidney
•Ascendofthekidney:Itascendsfrompelviccavitytoitsadult
siteinthelumbarregiononposteriorabdominalwall.Thisis
donebydorso-cranialelongationoftheureterpushingthe
kidney.
•Changeofbloodsupply:duringascend.
•Lossoffetallobulation:surfaceofthekidneybecomes
smooth.
•Changeofdirectionofhilum:fromanteriortomedial.

54. Partitioning of The Cloaca

55. Partitioning of The Cloaca

56. Partitioning of The Claoca

57. •Thedefinitivekidneyformedfromthemetanephrosbecomes
functionalnearthe12thweek.
•Urineispassedintotheamnioticcavityandmixeswiththeamniotic
fluid.
•Thefluidisswallowedbythefetusandrecyclesthroughthekidneys.
•Duringfetallife,thekidneysarenotresponsibleforexcretionof
wasteproducts,
•Theplacentaservesthisfunction.
Function of The Kidney

58. •Duringthefourthtoseventhweeksofdevelopmentthecloaca
dividesintotheurogenitalsinusanteriorlyandtheanalcanal
posteriorly.
•Theurorectalseptumisalayerofmesodermbetweenthe
primitiveanalcanalandtheurogenitalsinus.
•Thetipoftheseptumwillformtheperinealbody.
Bladder And Urethra

59. •Three portions of the urogenital sinus can be distinguished:
1.Theurinary bladder ,(the upper and largest part).
2.The pelvic part of the urogenital sinus, (narrow canal)
3.The phallic part of the urogenital sinus,(flattened from side to
side).
Bladder And Urethra

60. Divisions of the cloaca into the urogenital sinus and anorectal
canal. The mesonephricduct is gradually absorbed into the
wall of the urogenital sinus, and the uretersenter separately.

61. Initiallythebladderiscontinuouswiththeallantois,
•butwhenthelumenoftheallantoisisobliterated,theurachus,remains
andconnectstheapexofthebladderwiththeumbilicus.
•Intheadult,itisknownasthemedianumbilicalligament.
Bladder And Urethra

62. •Thecaudalportionsofthemesonephricductsareabsorbedintothewallofthe
urinarybladder.
•Theuretersenterthebladderseparately.
•Asaresultofascentofthekidneys,theorificesoftheuretersmovefarther
cranially.
During Differentiation of the Cloaca

63. •thoseofthemesonephricductsmoveclosetogethertoenter
theprostaticurethraandinthemalebecometheejaculatory
ducts.
•Withtimethemesodermalliningofthetrigoneisreplacedby
endodermalepithelium,sothatfinallytheinsideofthebladder
iscompletelylinedwithendodermalepithelium.
During Differentiation of the Cloaca

64. Separation of The Ureter

65. Separation of The Ureter

66. Urinary Bladder

67. Urinary Bladder & Urethra

68. Male Urethra

69. Female Urethra

70. The prostate gland is formed by buds from the urethra
Prostate Gland

71. Prostatic Gland

72. •Theepitheliumoftheurethrainbothsexesoriginatesinthe
endoderm;
•Attheendofthethirdmonth,epitheliumoftheprostaticurethra
beginstoproliferateandformsanumberofoutgrowthsthat
penetratethesurroundingmesenchyme.
•Inthemale,thesebudsformtheprostategland.
•Inthefemale,thecranialpartoftheurethragivesrisetothe
urethralandparaurethralglands.
Urethra

73. Wolffianducts
Art

74. Netter
Müllerianducts
Art

75. Acknowledgement

76. 76
Thank you

79. Development of Kidneys and Ureters
Three sets of successive kidneys develop in human embryos.
The first set—pronephroi—
is rudimentary and
nonfunctional
The second set—
mesonephroi—is well
developed and functions
briefly during the early fetal
period.
The third set—
metanephroiforms the
permanent kidneys.

80. Pronephros
These bilateral structures appear early in the fourth week.
They are represented by a few cell clusters and tubular structures
in the neck region
The pronephricducts run caudally and open into the Cloaca.
The pronephroisoon degenerate; however, most parts of the
pronephricducts persist and are used by the next set of kidneys.

81. Mesonephros
These large, elongated excretory organs appear late in the fourth week, caudal to the
pronephroi.
The mesonephroiare well developed and function as interim kidneys for approximately 4
weeks, until the permanent kidneys develop and function.
The mesonephrickidneys consist of glomeruli(10–50 per kidney) and tubules.
The mesonephrictubules open into bilateral mesonephricducts which open into the
cloaca.
The mesonephroidegenerate toward the end of the first trimester.

82. Metanephroi
Metanephroi—primordiaof permanent kidneys—begin to develop in
the fifth week and become functional approximately 4 weeks later.
The permanent kidneys develop from two sources:
(1) The uretericbud (metanephricdiverticulum)
(2) The metanephrogenicblastema(metanephricmass of mesenchyme)

83. A uriniferoustubule
consists of two
embryologically
different parts:
A nephronderived
from the
metanephrogenic
blastema
A collecting tubule
derived from the
uretericbud

84. Initially the primordial permanent kidneys lie close to each other in the pelvis.
As the abdomen and pelvis grow, the kidneys gradually relocate to the abdomen and move farther
apart. They attain their adult position by the ninth week (contact with the suprarenal glands).
This “ascent” results mainly from the growth of the embryo’s body caudal to the kidneys
Initially the hilumof each kidney, where blood vessels, the ureter, and nerves enter and leave, face
ventrally; however, as the kidneys relocate (“ascend”), they rotate medially almost 90 degrees.
By the ninth week, the hilaare directed anteromedially. Eventually the kidneys become
retroperitoneal (external to the peritoneum) on the posterior abdominal wall.
Positional Changes of Kidneys

85. Development of Urinary Bladder
•The urogenitalsinus is divided into three parts (imaginary):
A vesicalpart that forms most of the urinary bladder and is continuous
with the allantois.
A pelvic part that becomes the urethra in the neck of the bladder, the
prostatic part of the urethra in males, and the entire urethra in females
A phallic part that grows toward the genital tubercle (primordiumof
the penis or clitoris