Embryology of the UG system Flashcards Preview

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Flashcards in Embryology of the UG system Deck (43):

Urinary (and genital) system develops from

intermediate mesoderm of trilaminar disc


Intermediate mesoderm separates from lateral and paraxial mesoderm during folding and forms 

urogenital ridge



Pronephros (pronephric system) is nonfunctional cervical nephromtome. It is transitory and regresses by week 



Mesonephros is a primative kidney that develops in week 

  • 4
  • contains
    • functional glomeruli
    • Mesonephric tubules 
      • Mesonephric duct opens into cloaca


The mesonephric duct opens into 



Mesonephros are present and functional from weeks _____

  • 6-10


After week 10 the mesonephros degenerates except for 

  • The dcut sytem will contribue to part of the male genital system (ductus deferens)
  • Some vestigial structures in the female



Renogenesis involves a process of reciprocal induction, which is ____ dependent

retinoic acid


Cranial-caudal patterning establishes a "renogenic" region within the intermediate mesoderm in the tail of the embryo termed the 

  • Metanephric Blastema
    • The metanephric Blastema secretes growth factors that induce growth of the ureteric bud from the caudal portion of the mesonephric duct


Steps in Renogenesis

  • Involves a process of reciprocal induction, which is retinoic acid dependent
  • Cranial-caudal patterning establishes a "renogenic" region within the intermediate mesoderm in the tail of the embryo 
  • This renogenic mesoderm is the metanephric blastema
  • The metanephric blastema secretes growth factors that induce growth of the ureteric bud from the caudal portion of the mesonephric duct
  • The ureteric bud proliferates and responds by secreting growth factors that stimulates proliferation and then differentiation of the metanephric blastema into glomeruli and kidney tubules
  • Perturbations in any aspect of these inductive events (e.g. mutations of either metanephric or ureteric factors or disruption of retinoic acid signaling)  may cause inhibition of ureteric bud growth and renal hypoplasia or agenesis
  • Conversely, duplication or overproliferation of structures can also occur 


Ureteric bud derivatives

Collectin tubules/ducts ---> Minor Calyces ----> Major Calyces ----> Renal Pelvis ---> Ureters


In utero function of metanephros

  • Blood plasma from glomerular capillaries begins to be filtered by 10th week
  • Urine is produced, but the primary funciton is not to clear waste (placenta) but to supplement produciton of amniotic fluid 
  • Oligohydramnios (insufficient amount of amniotic fluid) may indicate bilateral renal agenesis or urethral obstruction


Accessory Renal Vessels

  • Kidneys are formed in pelvis but ascend to lumbar region with progressive revascularization from common iliac and aorta
  • Aberrant renal vessels enter the kidney independently from the primary renal vessels 
  • These occur in approximately 10% of individuals and 98% arise from the the abdominal aorta. Most enter the renal pelvis and pose little problem 
  • Aberrant arteries to the inferior pole of the kidney (4-6%)  may be the cause of obstruction of the ureter and may cause an intermittent or continuous obstruction to urinary drainage form the renal pelvis 


Renal Agenesis 


Renal Fusion 

  • Prevents normal rotation 
  • Abnormal blood supply 
    • usually from middle sacral or common iliac arteries
  • ectopic kidney 
    • may also be crossed with/without fusion
  • Horshoe kidney


 ___% of Horseshoe kidney presentation are fused at lower pole and usually found 

  • 90% of horshoe kidney's are fused at lower pole
  • Usually foudn inferior to inferior mesenteric artery




Wilm's Tumor

  • Cancer of the kidney
  • This usually affects children under the age of 5
  • Wilms' tumor is caused by motations in the WT1 gene


Development of the urinary bladder

  • The cloaca is divided by the urorectal septum
  • The DORSAL (inferior) portion develops into the rectum and anal canal 
  • The ventral (superior) portion develops into the BLADDER and UROGENITAL SINS, which will give rise to the bladder and lower urogenital tracts (prostatic and penile urethrae) in males; urethra and lower vagina in females)


Between weeks ___ -___, mesonephric duct and ureteric bud incorporation into posterior wall of urinary bladder



Ureteric buds open into bladder wall, while mesonephric ducts open more inferiorly into the ____

  • pelvic urethra
    • The triangular region of the incorporated mesonephric duct incorporated in the bladder wall forms the trigone


An ectopic ureter

  • the distal ureter acts as the ductus deferens and forms a trigone (this can lead to always being wet bc they have no sphincter to block the flow of urine)


Urachal Fistula or cyst

  • Bladder is continuous superiorly with allantois (which should collapse and become the urachus)
  • The urachus may remain patent through its length (C-urachal fistula) or only at an end (B-urachal sinus)
  • Remnants of the urachal lumen may also give rise to urachal cysts (A). These usually present as an abdominal mass


At what week does phenotypic sexual differentiation begin

Week 7



Male and Female external genitalia can be recognized at week



Phenotypic differentiation is complete at week 



Mullerian (paramesonephric) duct develops into:

  • Fallopian tubules 
  • uterus
  • upper part of vagina


Wolffian (mesonephric) duct develops into:

  • Epididymis
  • vas deferens 
  • seminal vesicle
  • ejaculatory duct


Synthesis of SRY protein (testis-determining factor, TDF) triggers ____ development






are paramesonephric and mesonephric ducts present during indifferent stage

  • yes 
    • testosterone leads to further development of Mesonephric duct
    • absence of testerone leads to further development of paramesonephric duct


Gonads develop from what tissue(s)

  • 3
    • epithelium of intraembryonic coelom
    • intermediate mesoderm
    • primordial germ cells
      • primordial germ cells from mesoderm of yolk sac invade the dorsal mesentery and migrate to urogenital ridges


External Genitalia development

  • Phallus
    • clitoris or penis
  • (Uro)genital folds
    • labis minora or shaft of the penis
  • Labioscrotal (Genital) swellings
    • labis majora or scrotum


46, XY can have persistence of paramesonephric ducts if 

the circulating levels of AMH are low or there is an abnormal response to normal AMH


Mullerian agenesis 

  • Failure of the paramesonephric ducts to develop 
  • Results in missing uterine tubes, uterus and variable malformations of the upper poriton of the vagina
  • Also called MRKH or Mayer-Rokitansky-Kuster-Hauser Syndrome



  • Incomplete fusion of the urethral folds
  • Urethra opens onto the ventral aspect of the penis
  • Can result form inadequate androgen production or inadequate receptor sites for DHT
  • Four types 
    • Gladular
    • Penile 
    • Penoscrotal 
    • Perineal 


Classic virilizing adrenal hyperplasia

  • Female intersex
  • Females (46, XX) with severe forms of adrenal hyperplasia have ambigous genitalia at birth due to excess adrenal androgen production in utero
  • Ambiguous genitalia ranges from complete fusion of the labioscrotal folds and a phallic urethra to only clitoromegaly, partial fusion of the labioscrotal folds, or both 
  • No abnormalities of ovaries 


Androgen Insensitivity Syndrome (AIS)

  • An X-linked disorder in which receptors remain unresponsive to androgens
  • Despite normal levels of testosterone, the male fetus fails to masculinise 
  • The external genitalia are feminine. Internally they possess non-functioning undescended testes
  • At puberty, secondary female sexual characteristics may appear due to estradiol from testosterone aromatization 
  • Such males not only physically resemble females, but also tend to be feminine in gender and maybe behavior
  • it is common to perform gonadectomies at puberty and for them to receive hormone therapy, to be reared as females 


5-alpha reductase deficiency (5-ARD)

  • Autosomal recessive condition resulting in the inability to convert testosterone to the more physiologically active dihydrotestosterone (DHT)
  • Because DHT is required for the normal masculinization of the external genitalia in utero, genetic males with 5-ARD are born with ambiguous genitalia (underdevelopment of penis and scrotum or pseudovaginal perineoscrotal hypospadias)
  • Derivatives of mesophric duct are normal 
  • often misdiagnosed as AIS
  • 'Guevedoche' or 'Machihembras' (first women, then man); third gender in some cultures 
    • this is because at puberty when testosterone levels get high enough they may masculinize)