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									HISTOLOGY &

     Teaching PPT

Dept. of Anat., Hist. & Embry.
    School of Medicine
 Xi’an Jiaotong University

Development of Urinary &
    Genital systems

   Tianbao Song (宋 天 保)
          Chapter 26 Development of
          Urinary and Genital System
I. Development of Urinary System
1. Development of Kidney and Ureter
 1.1 Primordia:
 •Cervical part →
 •Caudal part →
1.2 Pronephros:
Nephrotomes → pronephric tubules and duct →
pronephros → degenerates.
1.3 Mesonephros:
1) Nephrogenic cord → mesonephric ridge →
2) Mesonephric tubules → most disappear;
  mesonephric duct → open into cloaca.
1.4 metanephros
1) Primordia: ureteric bud and metanephric
     Mesonephric duct

2) ureteric bud → ureters, renal pelvis, calyces,
collecting tubules
3) Metanephric blastema → nephrons →
Bowman's capsule, renal tubules → open
connection to collecting tubules
4) Kidneys ascend → abdomen
2. Formation of Bladder and Urethra
Primordium: urogenital sinus
1) upper part → urinary bladder → continuous
   with allantois (obliterated later)
2) Middle part of urogenital sinus → urethra;
3) Lower part → penile urethra in males, vestibule in
3. Congenital Malformations
3.1 Polycystic kidney
•Abnormal development of the collecting system,
or failure of the collecting tubules and nephrons
to join;

•Kidney contains many
cysts, and failure of
renal function may be
3.2 Pelvic kidney
• Failure of kidney to ascend and still in the pelvis.
3.3 Horseshoe kidney
• Both kidneys fail to ascend, and their lower poles
fuse together.
3.4 Double ureter
•Early splitting of ureter completely or partially;
•Ureters open into bladder separately, or unite and
open as usual.
3.5 Urachal fistula
•Caused by persisting allantois.
•Urine may drain from the umbilicus.
II. Development of Genital System

1. Development of Gonads
1.1 Primordia: gonadal ridges (coelomic epithelium
+ mesenchyme), primordial germ cells.
1.2 Indifferent stage:
• Gonadal ridges →
primary sex cords.
• Yolk sac → primordial
germ cells migrate into
primary sex cords
1.3 Development of testis
1) Y → SRY → primary sex cords → medulla →
testicular cords → seminiferous tubules →
↗epithelial cells → Sertoli cells
↘primordial germ cells → spermatogonia
2) Mesenchyme (surface) → tunica albuginea;
    (between sex cords ) → Leydig cells →
1.4 Development of ovary
1) XX (no SRY) → primary sex cords → medulla →
2) Coelomic epithelium → secondary sex cords
(with primordial germ cells )
3) Secondary sex cords → cell clusters →
germ cells → oogonia
                                      Primordial follicles
epithelial cells → follicular cells

4) Oogonia → primary oocyte → no oogonia at
1.5 Descent of the testis
1) Mesenchyme → gubernaculums
( testis -- genital swelling)
2) Rapid body growth
                           → testis descent →
gubernaculum shortening

inguinal canal → scrotum
3) Peritoneal sac → vaginal process → scrotum
→ tunica vaginalis
4) Proximal part of vaginal process → obliterated
at birth.
2. Development of Genital Duct
2.1 Primordia: mesonephric duct, paramesonephric
2.2 Indifferent stage
1) Coelomic epithelium →
paramesonephric ducts:
• cranial end → body cavity;
• caudal ends fuse →
uterine canal.
2) Tip of uterine canal →
urogenital sinus → sinus
2.3 Development of male genital duct
1) Androgens (Leydig cells)→
•mesonephric duct → ductus epididymis, ductus
deferens, ejaculatory duct, seminal gland;
tubules →
efferent ductules
of testis.
2) Anti-Mullerian duct hormone (Sertoli cells)→
paramesonephric ducts regress.
2.4 Development of female genital duct (no A & AMH)
1) Paramesonephric duct → uterine tube;
Uterine canal → uterus, upper 1/3 of vagina.
2) Sinus tubercle → vaginal plate → canalized →
lower 2/3 of vagina.
3) Mesonephric ducts → degenerate.
3. Development of external genitalia
3.1 Primordia: urogenital folds, genital tubercle,
urogenital groove, labioscrotal swellings.
3.2 Development
                          Male (A)             Female(no A)
genital tubercle           phallus                clitoris
urogenital folds       lateral wall of urethra labia minora
labioscrotal swellings    scrotum               labia majora
urogenital groove        penile urethra            vestibule
4. Congenital Malformations
4.1 Cryptorchidism
•Failure of one or both
testes to descend into
•Seeming to be due to
abnormal androgen
•Testes may remain in
abdomen or in inguinal
4.2 Congenital inguinal hernia
•Failure of vaginal process to close;
•Intestinal loops may descend into scrotum.
4.3 Abnormalities of the uterus
•Defects of fusion of caudal ends of
paramesonephric ducts;
•May cause double uterus, bicornuate
uterus, uterus septus, etc.
4.4 Vaginal atresia
Caused by failure of vaginal plate to form or
to be canalized.
4.5 Hermaphroditism
1) True hermaphrodite has gonad and external
genitalia of both sexes. rarely observed.
•Has either testes (male)
or ovaries (female);
•External genitalia sex;
resembling opposite
•Inadequate (male) or
excessive (female)
androgen production.
4.6 Testicular feminization syndrome
• 44+XY chromosome complement;
• Devoid of androgen receptors;
• Testes in inguinal region, no spermatogenesis;
• External genitalia as in females; no uterine tubes,
4.7 Hypospadias
•Incomplete fusion of urogenital folds;
•Abnormal opening of urethra along ventral penis.
1. Primordia and developmental features
   of gonads & kidneys.
2. Sex differentiation of the gonads. 2.
3. Differentiation of the urogenital sinus;
4. Sex differentiation of the genital ducts.
5. Congenital malformations of genital

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