Embryology of the Urogenital System Flashcards
Name the three initial structures formed by condensation of the intermediate mesoderm.
Pronephros
Mesonepros
Metanephros
What structures does the pronephros give rise to?
NONE - the pronephros goes away.
What structures does the mesonephros give rise to?
- mesonephronic mesenchyme - gonads
- mesonephric duct - ureters (both sexes), male genital tubes
- paramesonephric duct - female genital tubes
Why does the ureteric bud form? Where does it from from?
The metanephric mesenchyme induces formation of a diverticulum from the mesonephric duct, the ureteric bud, that grows toward and into the metanephros.
What structures does the metanephros give rise to?
metanephric mesenchyme - true kidneys
What pathologic anatomy can arise from the process of inducing the ureteric bud?
Sometimes a second ureter may be induced, and this supernumerary ureter may drain beyond the urinary sphincter, or into the bladder, leading to incontinence.
How does the kidney maintain its (high) blood flow during its ascent from the pelvis to the abdomen? What abnormal anatomy may this lead to?
New arteries are formed along the iliac artery/aorta as it ascends, and these new arteries are resorbed once the kidney has moved beyond that location. If this resorption does not occur, then supernumerary arteries to the kidney are seen. This is not a problem unless the extra artery obstructs a ureter.
What is meant by a “horseshoe” kidney?
Normally the kidneys rise until they hit the adrenal glands, which stops their ascent. But kidneys may become entangled by, for example, the gonadal arteries and have their ascent arrested. Since they are rotating 90 degrees as they ascend, if they are prematurely stopped the caudal poles of the kidneys may fuse, forming a single organ. “Horseshoe” kidney.
How are the urogenital sinus and anorectum formed?
The cloaca septates - the urorectal septum is formed of splanchnic mesoderm covered with endoderm, and this septum fuses with the cloacal membrane to form the perineal body as well as 2 chambers, the anorectal canal and the urogenital sinus.
What is the adult structure that arises from the caudal tip of the urorectal septum?
The perineal body- a very important supportive structure
What happens if the cranial portion of the urogenital sinus fails to form properly?
Can result in urachal fistula, cysts, sinuses, or even extrophy of the bladder
How is gender determined, based on PRESENCE of the SRY gene?
SRY gene is on Y chromosome
Induces formation of Leydig & Sertoli cells
Leydig cells produce androgens
Sertoli cells produce Müllerian Inhibiting Substance
With androgens present, Primary Sex Cords persist
PSC -> seminiferous tubules, rete testes
Androgens support the survival of the Mesonephric duct
MIS induces apoptosis of the paramesonephric duct
How is gender determined, based on ABSENCE of the SRY gene?
Lack of SRY gene (no Y chromosome)
Lack of androgens
Primary sex cords undergo apoptosis
Secondary sex cords form -> follicular cells
Mesonephric duct dies (lack of androgens)
Paramesonephric duct lives (no MIS to kill it)
Identify the portions of the genital tubes or urogenital sinus that give rise to:
ductus deferens
seminiferous tubules
rete testes
urethra
ejaculatory ducts
prostate
seminal vesicles
bulbourethral gland
Mesonephric duct: ductus deferens, seminal vesicles, ejaculatory duct
Urogenital sinus: urethra -> prostate, bulbourethral bland
Primary sex cords -> seminiferous tubules, rete testes
Identify the portions of the genital tubes or urogenital sinus that give rise to:
uterine tubes
uterus
vagina
paraurethral glands
urethral glands
Paramesonephric duct: uterine tubes, uterus, vagina (superior)
Urogenital sinus endoderm -> urethra
Buds off of urethra -> paraurethral glands, urethral glands
