1. UROGENITAL SYSTEM DEVELOPMENT

2. There are three parts of mesoderm: Paraxial Intermediate
Intermediate Mesoderm Forms Much of the Urogenital System
There are three parts of mesoderm:
Paraxial
Intermediate
Lateral plate.
Most of the urinary and genital systems develop from the intermediate mesoderm.

3. Mesoderm in the Chick Embryo
Paraxial mesoderm (somite)
Intermediate mesoderm
Body cavity
Lateral plate mesoderm

4. Three consecutive kidney systems formed Pronephros Mesonephros
metanephros.
They form in the intermediate mesoderm that extends from cervical to pelvic regions along the posterior wall.

5. Pronephros:
segmented, forms in cervical regions, rudimentary, with little or no significance. (4th w)
Mesonephros: (4th w)
unsegmented, forms in thoracic and upper lumbar regions, may function briefly, consists of filtration units and a duct, degenerates almost completely in females, but contributes to the duct work of the male reproductive system.
Metanephros: (5th W)
definitive kidney system, forms in the pelvic region, begins functioning in the 10th to 12th weeks.
4.5 weeks
All three systems are never present at the same time

6. Intermediate Mesoderm Forms the Urogenital Ridge

7. Intermediate Mesoderm Forms the Urogenital Ridge
In lumbar region, the gonads develop from a proliferation of epithelium and condensation of underlying mesenchyme.
Together the gonads and mesonephros form the urogenital ridge. (retroperitoneal)
Excretory tubules form in the mesonephros and differentiate into Bowman’s capsule around a tuft of capillaries called the glomerulus (renal corpuscle). This is the filtration region for the kidney.

8. Intermediate Mesoderm Forms the Urogenital Ridge
The nephron consists of filtration units (Bowman’s capsule plus glomerulus) together with the excretory tubule.
Two ducts : mesonephric (wolfian) and paramesonephric (müllerian) ducts. Both ducts enter into the anterior portion of the cloaca that will form the urogenital sinus.

9. Intermediate Mesoderm Forms the Urogenital Ridge
mesonephric duct is the collecting duct for the mesonephric kidney and will contribute to the male reproductive ducts.
The paramesonephric duct parallels the mesonephric duct and contributes to the female reproductive system.

10. ureteric bud grows off the
The Ureteric Bud Forms as an Outgrowth from the Mesonephric Duct
ureteric bud grows off the
caudal end of the mesonephric duct and into intermediate mesoderm(metanephric
Blastema)in the pelvic region.
The bud is responsible for inducing mesoderm to form kidney.

11. Collecting System Forms from the Ureteric Bud
6-7 Weeks
The ureteric bud forms the collecting system for the definitive kidney in addition to ureter.
The ureteric bud lengthens and then starts to divide, eventually forming the renal pelvis, major and minor calyces, and collecting tubules for the definitive kidney.

12. The Ureteric Bud Induces the Metanephric Blastema to Form Filtration Units
As the ureteric bud branches in the metanephric blastema, it induces this mesoderm to form filtration units (nephrons).
Thus, the tubules formed and eventually developed into Bowman’s capsules around the glomeruli and proximal and distal convoluted tubules and Henle’s loops.

13. Kidneys are initially formed in the pelvic region and are said to “ascend” into their definitive location in the lumbar area
Renal function:
Time
excreation

14. Kidneys ascend from the pelvis to the lumbar region.
Ascent of the Kidneys
Kidneys ascend from the pelvis to the lumbar region.
This is mostly a passive process created by growth of the caudal region of the embryo and diminution of the body curvature.

15. Pelvic and Horseshoe Kidneys
Ureter
Pelvic kidney: kidney sticks in the pelvis during caudal growth of the embryo and fails to ascend.
Horseshoe kidney: in early development in the pelvis, the kidneys are in close proximity, and sometimes their tissues fuse. It is blocked in its ascent by the inferior mesenteric artery.
Wilms tumor: cancer of the kidneys affects children by 5 years age

16. Polycystic Kidney
Recessive form: 1:5000; cysts from collecting tubules; renal failure in infancy
Dominant form: 1: : cysts from anywhere (all regions of the nephrons); renal failure in adulthood

17. Complete and partial duplications may occur.
Duplications of the Ureters
Complete and partial duplications may occur.
Results from early splitting of the ureteric bud
They are not usually symptomatic but may make it more difficult to pass kidney stones.

18. Bladder Development
6 Weeks
7 Weeks
8 Weeks
Proctodeum
Initially, both the urinary system and the gut enter into a common chamber called the cloaca.
During 4th-7th week the urorectal septum will completely divide cloaca into rectal canal posteriorly and urogenital sinus anteriorly. The tip of the urorectal septum forms the perineal body.

19. urogenital sinus: Three portions :
Bladder Development
urogenital sinus: Three portions :
Upper (largest part) is the urinary bladder
pelvic part: in male gives rise to prostatic and membranous urethra
phallic part: as genital tubercle grows, this part of the sinus will be pulled ventrally
allantois connects bladder to umbilicus which later forms urachus (fibrous cord), ultimately be median umbilical ligament.

20. Consequently, ureters will enter bladder separately
Bladder Development: Incorporation of the Mesonephric Duct
bladder expansion: caudal mesonephric ducts absorbed into the posterior wall of urinary bladder (trigone : its mucosa is mesodermal then covered by endoderm ).
Consequently, ureters will enter bladder separately

21. Bladder Development: Incorporation of the Mesonephric Duct
ascent of the kidneys: orifices of ureters move farther cranially while those of mesonephric ducts enter prostatic urethra and in the male become vas deferens and ejaculatory ducts.
Notice that vas deferens crosses over the ureters. If the embryo is female, the mesonephric ducts degenerate.

22. Urethra Epithelium: endoderm C.T. and muscular tis: visceral mesoderm
end of third month: prostatic urethra epithelium proliferate and penetrate the surrounding mesenchyme.
In male, these buds form the prostate gland
In female, gives rise to urethral and paraurethral glands.

23. Possible Positions for Ectopic Ureters

24. Final Position of the Ureters and Mesonephric Duct (Vas Deferens)
In male: mesonephric ducts differentiate into the vas deferens, seminal vesicle and ejaculatory duct.

25. Urorectal Septal Defects and Imperforate Anus

26. bladder Abnormalities

27. Genital System
Relationship of the Genital Ridge to the Mesonephric System

28. 3rd W. formed in yolk sac endoderm (dorsal wall).
Migration of the Germ Cells
Germ cells:
3rd W. formed in yolk sac endoderm (dorsal wall).
4th W. migrate to the genital ridge along the hindgut through the dorsal mesentery.
5th W. They reach the ridge
6th W. they penetrate the ridge

29. Relationship of Germ Cells to the Epithelium of the Genital Ridge
6 Weeks

30. Formation of the Seminiferous Tubules
8 weeks
16 weeks
Sertoli cells: derived from epithelium; serve as nurse cells for sperm and produce antimüllerian hormone (AMH; also called müllerian-inhibiting substance [MIS])
Interstitial cells (of Leydig): derived from mesenchyme of genital ridge; secrete testosterone (mesonephric ducts, tubules, etc.; dihydrotestosterone, external genitalia)

31. Male Tubules and Ducts
16 Weeks
9 Months

32. Formation of Primary Oocytes and Follicular Cells

33. Derivatives of the Paramesonephric Ducts
8 Weeks
9 Months

34. Induction of the Vagina by the Paramesonephric Ducts
9 Weeks
12 Weeks
Newborn

35. Vaginal Development

36. Uterine Abnormalities

37. Testis and Ovary Development

38. Genetic Signals: Male vs. Female

39. External Genitalia: Indifferent Stage
4 Weeks
6 Weeks

40. Penis and Scrotal Development
10 Weeks
Newborn

41. Male
8 Weeks

42. Male
12 Weeks

43. Hypospadias
Glandular Hypospadius
Urethral and Glandular
Hypospadias

44. Female
11 Weeks

45. Female External Genitalia
Newborn
6 Weeks
5 Months

46. Female Pseudohermaphrodism (Adrenogenital Syndrome)

47. Androgen Insensitivity Syndrome (Testicular Feminization)

48. Signals for Sexual Differentiation
SRY
–SRY, +WNT4

49. Descent of the Testes
8 Weeks
19 Weeks
28 Weeks
Newborn
Cryptorchidism: Failure of the testes to reach the scrotal sac (3% of newborns)

50. Layers Covering the Testis

51. Indirect Inguinal Hernias and Hydroceles

52. Remnants of the Mesonephric Duct in Females