Development of urinary system

Dr. Mohamed Elfiky

1. Development of Urinary system
Dr. Mohamed El fiky
Professor of anatomy and embryology

2. Embryo after folding
Head swelling
Cardiac swelling
Umbilical cord
Y.S
G
U
T
Mohamed el fiky

3. •Three slightly overlapping
kidney systems are formed in a
cranial to caudal sequence
during intrauterine life in
humansin 3 stages :
•pronephros,
•mesonephros,
•metanephros. T
•The first of these systems is
rudimentary and
nonfunctional; the second may
function for a short time during
the early fetal period; the third
forms the permanent kidney.
Mohamed el fiky
Development of the kidney

4. Pronephros
•At the beginning of the fourth week,
the pronephrosis 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
pronephricsystem have
disappeared.
Mohamed el fiky

5. Mesonephros
•Themesonephrosandmesonephricductsarederivedfromintermediate
mesodermfromupperthoracictoupperlumbar(L3)segments.Earlyinthe
fourthweekofdevelopment,duringregressionofthepronephricsystem,the
firstexcretorytubulesofthemesonephrosappear.Theylengthenrapidly,form
anS-shapedloop,andacquireatuftofcapillariesthatwillformaglomerulusat
theirmedialextremity.AroundtheglomerulusthetubulesformBowman’s
capsule,andtogetherthesestructuresconstitutearenalcorpuscle.Laterally
thetubuleentersthelongitudinalcollectingductknownasthemesonephricor
wolffianduct.
Mohamed el fiky

6. •Inthemiddleofthesecondmonththe
mesonephrosformsalargeovoidorganoneach
sideofthemidline.Sincethedevelopinggonadis
onitsmedialside,theridgeformedbybothorgans
isknownastheurogenitalridge.Whilecaudal
tubulesarestilldifferentiating,cranialtubulesand
glomerulishowdegenerativechanges,andbythe
endofthesecondmonththemajorityhave
disappeared.Inthemaleafewofthecaudal
tubulesandthemesonephricductpersistand
participateinformationofthegenitalsystem,but
theydisappearinthefemale.
Mohamed el fiky

7. Metanephros
The Definitive Kidney
•The third urinary organ, the metanephros, or permanent kidney, appears in the fifth week. Its excretory units develop from
metanephricmesoderm in the same manner as in the mesonephric system. The development of the duct system differs from that of
the other kidney systems.
•Collecting System. Collecting ducts of the permanent kidney develop from the ureteric bud, an outgrowth of the mesonephric
duct close to its entrance to the cloaca .The bud penetrates the metanephrictissue, which is molded over its distal end as a cap .
Subsequently the bud dilates, forming the primitive renal pelvis, and splits into cranial and caudal portions, the future major calyces .
•Each calyx forms two new buds while penetrating the metanephrictissue. These buds continue to subdivide until 12 or more
generations of tubules have formed .Meanwhile, at the periphery more tubules form until the
Mohamed el fiky

8. •end of the fifth month. The tubules of the second order enlarge and
absorb those of the third and fourth generations, forming the minor
calycesof the renal pelvis. During further development, collecting
tubules of the fifth and successive generations elongate considerably
and converge on the minor calyx, forming the renal pyramid . The
ureteric bud gives rise to the ureter, the renal pelvis, the major and
minor calyces, and approximately 1 million to 3 million collecting
tubules.
•Excretory System. Each newly formed collecting tubule is covered
at its distal end by a metanephrictissue 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.
Mohamed el fiky

9. •These tubules, together with their glomeruli, form nephrons, or excretory
units. The proximal end of each nephron forms Bowman’s capsule, which is
deeply in-dented by a glomerulus . The distal end forms an open
connection with one of the collecting tubules, establishing a passageway
from Bowman’s capsule to the collecting unit. Continuous lengthening of the
excretory tubule results in formation of the proximal convoluted tubule,
loop of Henle, and distal convoluted tubule . Hence, the kidney develops
from two sources:
(a)metanephricmesoderm, which provides excretory units; and
(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
Mohamed el fiky

10. POSITION OF THE KIDNEY
•The kidney, initially in the pelvic region, later shifts to a more cranial position in the abdomen.
This ascent of the kidney is caused by diminution of body curvature and by growth of the body in
the lumbar and sacral regions
•In the pelvis the metanephrosreceives its arterial supply from a pelvic branch of the aorta. During
its ascent to the abdominal level, it is vascularized by arteries that originate from the aorta at
continuously higher levels. The lower vessels usually degenerate, but some may remain.
Mohamed el fiky

11. Mohamed el fiky

12. Congenital Abnormalities of kidney
1.Renal dysplasiasand agenesis: A spectrum of severe malformations that
represent the primary diseases requiring dialysis and transplantation in the
first years of life.
2.Congenital polycystic kidney: Numerous cysts form. The kidneys become
very large, and renal failure
occurs in infancy or childhood.
Mohamed el fiky
3.Duplication of the ureter:Results from
early splitting of the ureteric bud. Splitting
may be partial or complete, and
metanephrictissue may
be divided into two parts, each with its own
renal pelvis and ureter.
4-horseshoe kidney. The horseshoe
kidney is usually at the level of the lower
lumbar vertebrae, since its ascent is
prevented by the root of the inferior
mesenteric
5-pelvic kidneythe pelvis close to the
common iliac artery

13. Mohamed el fiky

14. DEVELOPMENT OF URINARY BLADDER
•During the fourth to seventh weeks of development thecloaca divides into the urogenital sinus anteriorly and the
anal canal posteriorly .
•(see Chapter 13). The urorectalseptum is a layer of mesoderm between the primitive anal canal and the urogenital
sinus. The tip of the septum will form the perineal body . Three portions of the urogenital sinus can be distinguished:
1.The upper and largest part 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.
2.The next part is a rather narrow canal, the pelvic part of the urogenital sinus, which in the male gives rise to the
prostatic and membranous parts of the urethra.
3.The last part is the phallic part of the urogenital sinus. It is flattened from side to side, and as the genital tubercle
grows, this part of the sinus will be pulled ventrally . (Development of the phallic part of the urogenital sinus differs
greatly between the two sexes: see Genital System; .
Mohamed el fiky

15. Mohamed el fiky

16. •Duringdifferentiationofthecloaca,thecaudalportionsofthemesonephricducts
areabsorbedintothewalloftheurinarybladder.Consequently,theureters,
initiallyoutgrowthsfromthemesonephricducts,enterthebladderseparately.Asa
resultofascentofthekidneys,theorificesoftheuretersmovefarthercranially;
thoseofthemesonephricductsmoveclosetogethertoentertheprostaticurethra
andinthemalebecometheejaculatoryducts.Sinceboththemesonephricducts
anduretersoriginateinthemesoderm,themucosaofthebladderformedby
incorporationoftheducts(thetrigoneofthebladder)isalsomesodermal.With
timethemesodermalliningofthetrigoneisreplacedbyendodermalepithelium,so
thatfinallytheinsideofthebladderiscompletelylinedwithendodermal
epithelium.
Mohamed el fiky

17. Mohamed el fiky

18. •Theepitheliumoftheurethrainbothsexesoriginatesintheendoderm;
thesurroundingconnectiveandsmoothmuscletissueisderivedfrom
splanchnicmesoderm.Attheendofthethirdmonth,epitheliumofthe
prostaticurethrabeginstoproliferateandformsanumberof
outgrowthsthatpenetratethesurroundingmesenchyme.Inthemale,
thesebudsformtheprostategland.Inthefemale,thecranialpartof
theurethragivesrisetotheurethralandparaurethralglands.
Mohamed el fiky
DEVELOPMENT OF URETHRA

19. Mohamed el fiky

20. Mohamed el fiky

21. TRIGONE PORTION
Mohamed el fiky

22. Bladder Defects
º When the lumen of the intraembryonic portion of the allantois persists, a urachal fistulamay cause urine to
drain from the umbilicus.
º If only a local area of the allantois persists, secretory activity of its lining results in a cystic dilation, a urachal
cyst.
º When the lumen in the upper part persists, it forms a urachal sinus.
Mohamed el fiky

24. º Exstrophyof the bladder: A ventral body wall defect in which the bladder mucosa is exposed. Epispadiasis a
constant feature and the open urinary tract extends along the dorsal aspect of the penis through the bladder to
the umbilicus.
May be caused by a lack of mesodermal migration into the region between the umbilicus and genital tubercle,
followed by rupture of the thin layer of
ectoderm. This anomaly is rare, occurring in 2/100,000 live births.
Mohamed el fiky