Development of the GU System

Question 1

The urogenital system is derived from?

Answer 1

Arises from intermediate mesoderm

Question 2

Describe the development of the intermediate mesoderm

Answer 2

It grows into the intraembryonic coelom and forms the urogenital ridge on each side. This will be the genital ridge medially and nephrogenic ridge laterally.

Question 3

What does the nephrogenic ridge give rise too?

Answer 3

Pronephros, mesonephros and metanephros.

Question 4

What is the function of the pronephrons

Answer 4

In the 4th week, the excretory units are seen and then disappear in the cervical region.

Question 5

A definitive kidney is formed from what two components?

Answer 5

Collecting portion and the excretory portion

Question 6

Describe features of the collecting portion

Answer 6

A ureteric buds sprout from caudal mesonephric ducts into metanephric mesenchymal cap. Bifurcation of the bud forms a primitive renal pelvis with subsequent generations forming major and minor calyces. Continued divisions penetrate into the metanephric tissue creating a pyramidal arrangement.

Question 7

Describe features of the excretory portion

Answer 7

The metanephric caps cover collecting tubules. This induces the tissue cap to form vesicles which lengthen and are penetrated by capillaries at one end while the other end unites with the collecting ducts. Further lengthening forms the characteristic nephron

Question 8

Describe the ascent of the kidneys

Answer 8

Growth in the lumbar and sacral regions cause the kidney to change its relative position superiorly. They rotate 90 degrees meaning the hilum moves medially. The aorta provides increasingly more branches to the developing kidneys

Question 9

Describe some congenital abnormalities of the kidneys

Answer 9

• They can form a horseshow kidney (where the inferior poles fuse)
• Pelvic kidney (failure of one of the kidneys to

Question 10

Describe the formation of the trigone

Answer 10

Ureteric buds and mesonephric ducts (later becomes ductus deferens) become incorporated into the posterior walls of the developing bladder. Ascent of the kidneys and growth of the bladder draws the ureteric entry to the bladder cranially which aids formation of the trigone

Question 11

Describe features of the indifferent gonad

Answer 11

Primordial germ cells within the yolk sac migrate via dorsal mesentery to intermediate mesoderm. Proliferating epithelium will form somatic supportive cells which envelop the PGCs forming primitive sex cords

Question 12

Describe the initial stage of male development

Answer 12

It is triggered by the presence of the SRY gene. The somatic support cells develop into sertoli cells. Primary sex cords form testies cords which engulf PGCs. Rete testies connect mesonephric tubules to the testis cords. Between coelomic epithelium and testies cords forms the tunica albuginea

Question 13

Describe the function of sertoli cells in the role of male development

Answer 13

• Sertoli cells secrete AMH (anti-mullerian hormone) which results in the degeneration of paramesonephric duct,
• Sertoli cells stimulate gonadal ridge cells to form leydig cells (secrete testosterone) Testosterone induces formation of epididymis, vas dererens and seminal vesicles. Dihydrotestosterone induces male specific external genitalia development and prostate.

Question 14

Describe features of persistent mullerian duct syndrome

Answer 14

Occurs due to mutations of AMH or AMH receptor genes so the paramesonephric duct fails to regress. It presents with uterus, vagina and uterine tubes, testes in the ovarian location and male external genitalia

Question 15

Describe the descent of the testes

Answer 15

They are pulled caudally by the gubernaculum. Failure of one or both of the testes to descend is cryptochidism

Question 16

Describe the development of the male accessory glands and their tissue of origin

Answer 16

Prostate and bulbourethral glands - endodermal invaginations from the urethra.
Seminal vesicle - Develops from mesonephric duct

Question 17

Describe the initial stage in female development

Answer 17

It occurs in the absence of SRY transcription factor. Germ cells therefore differentiate into oogonia and then primary oocytes. Somatic support cells differentiate into granulosa cells and surrounds the primary oocytes which forms the primordial follicles in the ovary.

Question 18

What is the role of thecal cells in female development

Answer 18

Produces oestrogen which along with maternal sources stimulates formation of female external genitalia and development of paramesonephric ducts. These ducts give rise to uterine tubes, uterus and superior vagina

Question 19

Name the three parts of the paramesonephric duct in the female

Answer 19

Crainial portion which opens up into the coelomic cavity.
Horizontal portion which crosses mesonephric duct,
Caudal portion which fuses with paramesonephric duct on opposite side

Question 20

Describe the formation of the uterovaginal canal

Answer 20

The fused caudal portion of the paramesonephric ducts give rise to the uterus and superior vagina. The vagina lumen is created by vacuolization of the paramesonephric duct. This also creates fornices

Question 21

What are some of the abnormal variations of the female development

Answer 21

• Double uterus and double vagina,
• Double vagina,
• Bicornate uterus,
• Septated uterus,
• Unicornate uterus,
• Cervical atresia

Question 22

Describe the appearance of the external genitalia in its indifferent stage

Answer 22

Week four - Genital tubercle, Cloacal membrane surrounded by cloacal folds and genital swellings.
Week Six - Urorectal septum forms so it produces distinct urethral folds and anal folds.

Question 23

Describe the external genitalial development of the male

Answer 23

The genital swellings become the scrotal swellings. The urethral fold begins to develop and within this is the urethral plate which folds to form a lumen and then extends. The prepuce (foreskin) is formed by circular ingrowth of ectoderm around the periphery of the glans.

Question 24

What is hypospadias?

Answer 24

Where the external urethral opening lies in an abnormal position along the ventral aspect of the penis