Development of urogenital system - I

1. Development of Urogenital System- I
Dr. Prabhakar Yadav
Assistant Professor
Department of Human Anatomy
B.P. Koirala Institute of Health Sciences

2. Urinary system - Intermediate mesoderm & Primitive cloaca.
Urogenital ridge: After folding of embryo, Intermediate mesoderm forms a longitudinal elevation along dorsal body wall on each
side of dorsal aorta/dorsal mesentery of gut.
Genital ridge: Medial part ; gives rise to genital system
Nephrogenic cord: Lateral part ; gives rise to the urinary system

3. kidney - 4th week of IUL
Nephrogenic cord:
Forms a longitudinal ridge on dorsal abdominal wall on each side of dorsal aorta
Extends from cervical to sacral region; covered by celomic epithelial, lining of
peritoneal cavity (celomic cavity)
• Cloaca: Part of hindgut caudal to attachment of allantois
• urorectal septum
• Ventral part - primitive urogenital sinus
• Dorsal part- primitive rectum

4. Nephrogenic cord forms three successive kidneys:
Pronephros, Mesonephros & Metanephros
Pronephros: Forms at 4th week in cervical region
Is nonfunctional so degenerates; pronephric duct— persists- Opens in cloaca.
Pronephric duct is attached to mesonephros - forms mesonephric duct.

5. Mesonephros : forms at end of 4th week in thoracolumbar region.
Is functional for short period & degenerates.
Mesonephric (excretory) tubules develop in mesonephros - drain into mesonephric duct.
Most of mesonephric tubules disappear, caudal tubules are modified- form of vasa efferentia of testis.
Metanephros : forms at beginning of 3rd month in sacral region; persists permanently; drains into ureter.

6. Kidney Develops from 2 sources:
(a) Metanephros- forms secretary system
(b) Ureteric bud- forms collecting system
Development of Collecting System
• Ureteric bud - Mesonephric duct; grows cranially
behind peritoneal cavity towards metanephros.
• Distal end of ureteric bud becomes capped by
metanephric blastema.
• Growing end of ureteric bud becomes dilated like a
funnel to form renal pelvis.
• Renal pelvis undergoes repeated divisions to form
major calyces, minor calyces, collecting Ducts &
collecting tubules
• Ureteric bud divides dichotomously & its 13
generations form collecting system of kidney
• Pelvicalyceal system

7. Development of Excretory System:
Cells of Metanephros form Metanephric blastema -
It come in contact with collecting tubule - condense around
tubule -- Metanephric cap.
Metanephric cap - converted into -Metanephric vesicle.
Metanephric vesicle: pear-shaped vesicle- S shaped tubule -
primitive renal tubule
Proximal end of primitive renal tubule is narrow -lie adjacent
to collecting tubule

8. Distal dilated end of primitive renal tubule forms : Bowman’s capsule - invaginated by a tuft of capillaries to form
Renal glomerulus.
Primitive renal tubule- forms Nephron (excretory unit)- glomerular (Bowman’s) capsule, PCT, loop of Henle & DCT
Distal convoluted tubule joins with collecting tubule : Uriniferous tubule.

9. Ascent of Kidney:
• At first lies in sacral region.
• Later ascends to thoracolumbar region (T12–L3)
• Ureter elongates accordingly as kidney ascends.
Arterial Supply of the Kidney
• Initially in pelvis –supplied-by median sacral artery- pelvic continuation of the aorta.
• Supplied by higher lateral splanchnic branches of aorta at successively higher levels.
• Definitive renal artery arises at L2 & represents lateral splanchnic branch of aorta.

10. Rotation of the Kidneys
• At first hilum of each kidney faces anteriorly
• During the ascent of kidney it rotates 90° medially; hilum of each kidney faces medially

11. Congenital anomalies of kidney
1. Renal agenesis (unilateral/Bilateral) : Occurs when ureteric bud fails to develop.
Ureteric bud induces metanephric tissue to form metanephric blastema.
2. Duplication of the kidneys: occur due to division of metanephric diverticulum.
• Incomplete division leads to a divided kidney with a bifid ureter.
• Complete division results in a double kidney with bifid or separate ureters

12. 3. Congenital polycystic kidney:
Numerous cysts filled with urine are present in the substance of kidney
Occurs due to abnormal dilatation of different parts of uriniferous
tubules, especially loops of Henle.
4. Anomalies of Shape:
a. Horseshoe kidney: Inferior poles of both kidneys are fused.
During ascent, horseshoe kidney gets trapped underneath inferior
mesenteric artery
Ureters arise from anterior surface of kidney & pass in front of isthmus

13. b. Lobulated kidney:
Fetal kidney- lobulated - disappears during 1st year after birth
if it fails to do so -leads to lobulated kidney.
c. Pancake kidney: 2 kidneys fuse to form a single mass that lies
in midline or on one side

14. 5. Anomalies of Position:
a. Pelvic kidney: kidney is located in the pelvis. Occurs when kidney fails to ascend
b. Incomplete Ascent: Lie opposite lower lumber vertebrae
c. Kidneys may ascend with in thoracic cavity
d. Both kidney may lie on one side of the midline
e. kidneys may be displaced to opposite side; two ureters cross each-other in midline

15. 6. Abnormal rotation
a. Non- rotation: Hilum directed forward
b. Incomplete roation: Hilum directed anteromedially
c. Reverse rotation: Hilum directed anterolaterally
7. Aberrant Renal arteries:
Blood supply partially or entirely form arteries arising at an abnormal level. –
-May lead to hydronephrosis.

16. Development of Ureter
Develops from ureteric bud- diverticulum from mesonephric (Wolffian) duct, just before it opens onto cloaca
(vesicourethral canal).
Parts of mesonephric ducts, caudal to the origin of the ureteric buds are absorbed into vesico-uretheral canal, so
that mesonephric ducts and ureteric buds have separate openings into the cloaca.

17. Anomalies of ureter
1. Double renal pelvis: due to division of ureteric bud
near its termination.
2. Bifid ureter: due to division of ureteric bud in lower third of
course
3. Double ureters: due to division of ureteric bud as it arises from
mesonephric duct
4. Ectopic ureter: Ureter does not open into urinary bladder as
ureter is not incorporated into Trigone of bladder
(a) In males- ureter opens into:
neck of urinary bladder, ductus deferens, seminal vesicles, rectum
or prostatic part of urethra.
(b) In females- into bladder neck, urethra, vagina or rectum
incontinence of urine is a common complain.

19. 6. Postcaval ureter: It occurs if right ureter ascends posterior to inferior vena cava.

20. Urinary Bladder:
Endodermal cloaca- divided by mesodermal urorectal septum during 4-7th Wk of IUL
Anterior part – Primitive Urogenital sinus ; Posterior part - Primitive rectum
Tip of urorectal septum forms: perineal body.
Cloacal membrane divides into:
Anteriorly- Urogenital membrane
posteriorly - Anal membrane

21. Mesonephric ducts - Open into primitive urogenital sinus that
becomes divisible into two parts by openings of ducts.
Vesicourethral canal -Part above the openings of mesonephric duct
Definitive urogenital sinus - Part below the opening.
vesicourethral canal
Upper large part of expands- urinary bladder
lower narrow part- forms primitive urethra.
Definitive urogenital sinus is further divided into two parts:
(a) cranial pelvic part (b) caudal phallic part .

22. Allantois: opens at cranial end of vesicourethral canal.
--Obliterates & forms a fibrous band- urachus -extends from apex of urinary bladder to umbilicus.
---Urachus is called median umbilical ligament in adult.

23. • Parts of mesonephric ducts caudal to ureteric buds are absorbed into the wall of vesicourethral canal.
• Mesonephric ducts and ureters open separately
• As kidneys ascend, openings of ureters move upward and laterally.

24. Trigone of Urinary Bladder:
-Triangular area on dorsal wall of vesicourethral canal between openings of ureteric buds & mesonephric ducts.
- derived from absorption of mesonephric ducts.

25. Development of Coats of Bladder Wall
1. Epithelial lining of whole of urinary bladder- endodermal vesicourethral canal,
except trigone of urinary bladder - mesodermal derived from the absorbed parts of mesonephric ducts.
2. Muscular & Serous coats- from splanchnopleuric intraembryonic mesoderm.

26. Anomalies
1. Urinary bladder may be absent or duplicated
2. Lumen of bladder may be divided into compartments by septa
3. Hourglass Bladder may be divided into upper and lower compartments
4. Bladder may communicate with rectum/Vagina

27. Ectopia vesicae:
• Lower median part of anterior abdominal wall & anterior wall of the urinary bladder is absent.
• Mucosal surface of posterior wall of urinary bladder showing ureteric orifices is exposed.
• Urine can be seen dribbling intermittently from ureteric orifices.
• Epispadias is a constant feature in this condition.
Occurs due to lack of migration of mesoderm in lateral folds of the embryo in the hypogastric region
Normally they grow medially and fuse with each other.

28. Female Urethra
Develops from- narrow caudal part of vesicourethral canal
except
small terminal part - pelvic part of definitive urogenital sinus.
phallic part of definitive urogenital sinus :
forms - vestibule of vagina into which the urethra opens
Female urethra corresponds to - prostatic part of male
urethra above ……………………...
Whole of female urethra is endodermal in origin except
its dorsal wall that is mesodermal, derived from absorption of mesonephric
ducts

29. Male Urethra:
Prostatic part:
Above openings of ejaculatory ducts - Caudal part of vesicourethral canal
Below openings of ejaculatory ducts- Upper pelvic part of definitive
urogenital sinus.
Posterior wall of prostatic part- Absorbed mesonephric ducts.
Membranous urethra: lower pelvic part of definitive urogenital sinus.

30. Spongy part: Bulbar part & Penile part - from phallic part of definitive urogenital sinus
except
Navicular part - from surface ectoderm.
Epithelium of the urethra is derived from endoderm.
Connective tissues & smooth muscles - derived from splanchnopleuric layer of intraembryonic mesoderm.

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