Development of the GU System Flashcards
The urogenital system is derived from?
Arises from intermediate mesoderm
Describe the development of the intermediate mesoderm
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.
What does the nephrogenic ridge give rise too?
Pronephros, mesonephros and metanephros.
What is the function of the pronephrons
In the 4th week, the excretory units are seen and then disappear in the cervical region.
A definitive kidney is formed from what two components?
Collecting portion and the excretory portion
Describe features of the collecting portion
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.
Describe features of the excretory portion
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
Describe the ascent of the kidneys
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
Describe some congenital abnormalities of the kidneys
- They can form a horseshow kidney (where the inferior poles fuse)
- Pelvic kidney (failure of one of the kidneys to
Describe the formation of the trigone
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
Describe features of the indifferent gonad
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
Describe the initial stage of male development
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
Describe the function of sertoli cells in the role of male development
- 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.
Describe features of persistent mullerian duct syndrome
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
Describe the descent of the testes
They are pulled caudally by the gubernaculum. Failure of one or both of the testes to descend is cryptochidism
Describe the development of the male accessory glands and their tissue of origin
Prostate and bulbourethral glands - endodermal invaginations from the urethra.
Seminal vesicle - Develops from mesonephric duct
Describe the initial stage in female development
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.
What is the role of thecal cells in female development
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
Name the three parts of the paramesonephric duct in the female
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
Describe the formation of the uterovaginal canal
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
What are some of the abnormal variations of the female development
- Double uterus and double vagina,
- Double vagina,
- Bicornate uterus,
- Septated uterus,
- Unicornate uterus,
- Cervical atresia
Describe the appearance of the external genitalia in its indifferent stage
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.
Describe the external genitalial development of the male
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.
What is hypospadias?
Where the external urethral opening lies in an abnormal position along the ventral aspect of the penis
