1. Urogenital System Development

2. Quick review

3. Embryo folding
One month

5. The urogenital system develops from the intermediate mesenchyme inthe dorsal wall of the embryo
A longitudinal elevation of the mesenchyme—the urogenital ridge—forms on each side of the dorsal aorta
The part of the urogenital ridge that gives rise to the urinary system is the nephrogenic cord (lateral)
the part that gives rise to the genital system is the gonadal ridge (medial)

6. DEVELOPMENT OF URINARY SYSTEM
The urinary system develop before the genital system(4th week)
Three sets of kidneys, develop in human embryos.
The first set—the pronephroi—is rudimentary and never functions.
The second set—the mesonephroi—is well developed and functions for a brief period.
The third set—the metanephroi—becomes the permanent kidneys.

7. Pronephroi appear early in the fourth week of development.
The pronephric ducts run caudally and open into the cloaca
The pronephroi degenerate but most of the pronephric ducts persist and are used by the next set of kidneys.

8. Mesonephroi appear late in the fourth week caudal to the pronephroi
function as interim kidneys until the permanent kidneys develop
The mesonephroi consist of glomeruli and mesonephric tubules
The tubules open into the mesonephric ducts, originally the pronephric ducts.

9. The meso-nephroi degenerate toward the end of the first trimester;
however, their tubules become the efferent ductules of the testes,
the mesonephric ducts have several adult derivatives in the male

10. Metanephroi
begin to develop early in the fifth week and start to function approximately 4 weeks later.
The urine is excreted into the amniotic cavity.
The permanent kidneys develop from two sources of mesodermal origin:
The ureteric bud
The metanephric blastema

11. The ureteric bud is an outgrowth from the mesonephric duct, near the cloaca, and is the primordium of the ureter, renal pelvis, calices, and collecting tubules
The elongating bud penetrates the metanephrogenic blastema—a mass of cells derived from the nephrogenic cord—that forms the nephrons

12. The stalk of the ureteric bud becomes the ureter,
undergoes repetitive branching to form the collecting tubules,major calices minor calices.
The end of each arched collecting tubule induces clusters of mesenchymal cells in the metanephrogenic blastema to form small metanephric vesicles

14. These vesicles elongate and become the renal tubules
Each distal convoluted tubule contacts an arched collecting tubule.
The tubules become confluent, forming a uriniferous tubule.

15. The fetal kidneys are subdivided into lobes
The fetal kidneys are subdivided into lobes. The lobulation usually disappears during infancy as the nephrons increase and grow.
At term, nephron formation is complete—each kidney containing approximately 1.5 million nephrons.
Functional maturation of the kidneys occurs after birth

16. Positional Changes of Kidneys
The metanephric kidneys lie close to each other in the pelvis
The caudal part of the embryo grows away from the kidneys so that the kidneys occupy progressively higher cranial levels.
As the kidneys change their positions “ascend,” they rotate medially almost 90 degrees. By the ninth week, the kidneys come in contact with the suprarenal glands as they attain their adult position

17. Changes in Blood Supply of Kidneys
Initially, the renal arteries are branches of the common iliac arteries
Later, the kidneys receive their blood supply from the distal end of the aorta
The kidneys receive their most cranial arterial branches from the abdominal aorta which become the renal arteries.
Normally, the caudal primordial branches undergo involution and disappear.

19. Unilateral renal agenesis
Boys are affected more often than girls
left kidney is usually the one that is absent
other kidney usually undergoes compensatory hypertrophy

20. Bilateral renal agenesis
incompatible with postnatal life
Failure of the Uretric budto penetrate the metanephrogenic blastema

21. Ectopic Kidneys
Most ectopic kidneys are located in the pelvis, but some lie in the inferior part of the abdomen.
Pelvic kidneys and other forms of ectopia result from failure of the kidneys to “ascend.”

22. MALROTATION OF THE KIDNEYS
If the kidney does not rotate, the hilum faces anteriorly (embryonic position)
If the hilum faces posteriorly, then rotation has progressed too far; if it faces laterally, then medial rotation has occurred.

23. DUPLICATIONS OF THE URINARY TRACT
These anomalies result from division of the metanephric diverticulum.
Incomplete division of the ureteric primordium results in a divided kidney with a bifid ureter
Complete division results in a double kidney with a bifid ureter or with separate ureters
A supernumerary kidney with its own ureter probably results from the formation of two metanephric diverticula.

25. Crossed fused renal ectopia
The developing kidneys fuse while they are in the pelvis,
and one kidney “ascends” to its normal position, carrying the other one with it.

26. Discoid kidney(Lump Kidney) resulting from fusion of the kidneys while they were in the pelvis.

27. Horseshoe Kidney
the poles of the kidneys are fused (usually the inferior poles)
Normal ascent of the fused kidneys is prevented because they are caught by the root of the inferior mesenteric artery.

28. PELVI-URETERIC JUNCTION (PUJ) OBSTRUCTION
congenital PUJ obstruction but may be as a result of:
abnormal merging of the ureter into the renal pelvis,
abnormal arrangement of ureteric musculature at the PUJ
crossing vessel (usually artery) running in front of the PUJ causing an obstruction.

29. The classic symptoms of a PUJ obstruction are:
Flank pain – often worsened after consuming large volumes of fluids, especially alcohol
Recurrent urinary tract infections
Blood in urine (haematuria)
Rx: Pyeloplasty

30. Vesicoureteral reflux
Insufficient sub mucosal tunneling and valve development as the ureter is incorporated into the urinary bladder.

31. Development of Urinary Bladder
Division of the cloaca by the urorectal septum into a dorsal rectum and a ventral urogenital sinus
the urogenital sinus is divided into three parts:
A cranial vesical part that forms most of the bladder and is continuous with the allantois
A middle 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 caudal phallic part that grows toward the genital tubercle—the primordium of the penis or the clitoris

33. Initially, the bladder is continuous with the allantois
The allantois soon constricts and becomes a thick, fibrous cord, the urachus
In adults, the urachus is represented by the median umbilical ligament.

34. Urachal cysts:
The most common site for these cysts is in the superior end of the urachus, just inferior to the umbilicus.

35. Two types of urachal sinuses :
one that opens into the bladder and one that opens at the umbilicus.

36. Patent urachus or urachal fistula.

37. distal parts of the mesonephric ducts are incorporated into its dorsal wall and contribute to the formation of the connective tissue in the trigone of the bladder.
The epithelium of the entire bladder is derived from the endoderm of the urogenital sinus.
As the mesonephric ducts are absorbed, the ureters come to open separately into the urinary bladder
In males, the orifices of the mesonephric ducts move close together and enter the prostatic part of the urethra as the caudal ends of these ducts become the ejaculatory ducts.
In females, the distal ends of the mesonephric ducts degenerate

39. Development of Urethra
The epithelium of most of the male urethra and the entire female urethra is derived from the endoderm of the urogenital sinus
The distal part of the urethra in the glans of the penis is derived from a solid cord of ectodermal cells

40. Hypospadias
Hypospadias is the most common anomaly involving the penis and is found in 1 in 300 male infants.
In glanular hypospadias, the external urethral orifice is on the ventral surface of the glans penis
Hypospadias results from inadequate production of androgens by the fetal testes, inadequate receptor sites for these hormones, or both.

42. DEVELOPMENT OF THE REPRODUCTIVE SYSTEMS
The gonads arise from intermediate mesoderm within the urogenital ridges of the embryo
The genital ducts arise from paired mesonephric and paramesonephric ducts
The mesonephric ducts give rise to MALE genital ducts
The paramesonephric ducts give rise to FEMALE genital ducts

43. DEVELOPMENT OF GONADS
The early genital systems in the two sexes are similar; therefore, the initial period of genital development is referred to as the indifferent state of sexual development
Gonadal development begins during the fifth week
Before the seventh week, the gonads of the two sexes are identical in appearance and are called indifferent gonads
The gonads (testes and ovaries) are derived from three sources:
Mesothelium (mesodermal epithelium) lining the pos-terior abdominal wall
Underlying mesenchyme
Primordial germ cells: originate in the wall of the umbilical vesicle and migrate along the dorsal mesentery of the gut to the gonadal ridges (from the 4th to 6th week)

45. Development of Testes
A coordinated sequence of genes induces the development of testes.
The SRY gene for the testis-determining factor (TDF) on the short arm of the Y chromosome acts as the switch that directs the development of the indifferent gonad into a testis.

46. . The connection of the prominent gonadal cords—the semini-ferous cords—with the surface epithelium is lost when the tunica albuginea develops.
The seminiferous cords develop into the seminiferous tubules, the straight tubules (tubuli recti), and the rete testis.

47. The seminiferous tubulesare separated by the mesen-chyme, giving rise to the interstitial cells(of Leydig). By the eighth week, these cells secrete androgenic hormones— testosteroneand androstenedione—that induce mascu-line differentiation of the mesonephric ducts and the external genitalia.
The seminiferous tubules remain solid (i.e., without lumina) until puberty, when lumina begin to develop.
The fetal testes also produce a glycoprotein known as müllerian-inhibiting substance (MIS) or antimüllerian hormone. MIS is produced by the sustentacular (Sertoli) cells, which are present until puberty, at which time the levels of MIS decrease.
MIS suppresses the development of the paramesonephric ducts, which form the uterus and uterine tubes. The semi-niferous tubules remain until puberty (i.e., without lumina), when lumina begin to develop.

48. The rete testisbecomes continuous with 15 to 20 mesonephric tubules that become efferent ductules.
These ductules are connected with the mesonephric duct, which becomes the ductus epididymis

50. Descent of the testes
The testes arise in the lumbar region but then descend into pelvic cavity and through the inguinal canal to end up in the scrotum
Descent of the testis is due to tethering of the testes to the anterior body wall by the gubernaculum.
With growth and elongation of the embryo coupled with shortening of the gubernaculum, the testes are pulled through the body wall, then the inguinal canal, and finally into the scrotum.

54. Development of Ovaries
Gonadal cordsextend into the medulla of the ovary and form a rudimentary rete ovarii that degenrates shortly
As the secondry cortical cords increase in size, primordial germ cellsare incorporated into them.
At approximately 16 weeks, these cortical cords begin to break up into isolated cell clusters—primordial follicles—each of which consists of an oogonium(derived from a primordial germ cell), sur-rounded by a single layer of follicular cells derived from the surface epithelium

56. Development of Male Genital Ducts
These ductules open into the mesonephric duct, which has been transformed into the duct of the epididymisin this region.
Distal to the epididymis, the mesonephric duct acquires a thick investment of smooth muscle and becomes the ductus deferens.
The Distal part of the mesonephric duct becomes the ejaculatory duct.

57. Seminal Gland A lateral outgrowth from the caudal end of each mesonephric duct gives rise to the seminal gland(vesicle). The secretions of this pair of glands nourish the sperms
Prostate Multiple endodermal outgrowths arise from the prostatic part of the urethra and grow into the sur-rounding mesenchyme

58. Development of Female Genital Ducts and Glands
The uterine tubesdevelop from the unfused cranial parts of the paramesonephric ducts
The caudal, fused portions of these ducts form the uterovaginal primordium, which gives rise to the uterus and the superior portion of the vagina

59. The vaginal epithelium is derived from the endoderm of the urogenital sinus. The fibromuscular wall of the vagina develops from the surrounding mesenchyme.
Formation of a vaginal plate
The central cells of this plate break down, forming the lumen of the vagina. The peripheral cells of the plate form the vaginal epithelium or lining
Outgrowths from the urogenital sinus form bilateral greater vestibular glands(of Bartholin) in the lower one third of the labia majora.

61. Double Uterus
A double uterus (uterus didelphys) results from failure of fusion of the inferior parts of the paramesonephric ducts
It may be associated with a double or a single vagina
In many of these cases, the indi viduals are fertile, but may have an increased incidence of premature delivery.

62. Summary of male urogenital tract derivatives
Ureteric bud: ureter
Mesonephric ducts: rete testis, efferent ducts, epididymis, vas deferens, seminal vesicle, trigone of bladder
Urogenital sinus: bladder (except trigone), prostate gland, bulbourethral gland, urethra

63. Summary of female urogenital tract derivatives
Ureteric bud: ureter
Mesonephric ducts: trigone of bladder
Paramesonephric ducts: oviduct, uterus, upper 1/3 of vagina
Urogenital sinus: bladder (except trigone), vestibular gland, urethra, lower 2/3 of vagina