Embryology Development of urogenital tract Flashcards
The urogenital system develops from?
Intermediate mesoderm
What is the name of the longitudinal elevation that appears either side of the aorta?
Urogential ridge
Of the urogenital ridge what is the name given to the part that develops into the urinary system/gential system?
Urinary system → Nephrogenic cord
Genital system → gonadal ridge
The urinary system develops in 3 distinct regions.
What are theses regions? When do the develop & when are they functional?
Cranial → caudal
Pronephros, week 4, never functional
Mesonephros, week 4, function weeks 6-10
Metanephros, week 4, functions from week 12
What is the origin of
1) excretory units
2) collection ducts
1) Metanephric mesoderm (matenephric blastema)
2) Ureteric bud (outpouch of mesonephric duct)
How does the position of the kidney change during development?
Develops in pelvis region, ascends to more cranial position and rotates by 90 degrees.
Renal agenesis can occur if…
How common is unilateral agenesis?
the ureteric bud fails to contact and/or induce the metanephric mesoderm
1/1000 more common on the L and in males. Associated with single umbilical artery
Bilateral renal genesis
Oligohydraminos
1/3000
Characteristic facial appearance → potters sequence
How does a duplication of the kidney occur?
Early splitting of ureteric bud, may be partial or complete
Why do accessory renal arteries form? How common is this?
Persistence of embryonic vessels formed during the ascent of the kidney.
25% of adult kidney have 2-4 renal arteries.
What structure is the forming bladder continuous with?
When it obliterates what is it remnant called?
The bladder is continuous with the allantois. Becomes obliterated to form the urachus (median umbilical ligament)
What are the organs of the epithelium of the urethra and the surrounding connective tissue/smooth muscle?
Inner epithelium: Endoderm
Outer smooth: Mesoderm
Why does a urachal fistula or urachal cyst form?
Urachal fistula: entire urachus remains open
Urachal cyst: small area persists
What is bladder exstrophy?
At birth, posterior wall of bladder protrudes through the abdominal wall, associated epispadias and wide separation of pubic bones.
Cause by lack of migration and incomplete closure of the inferior abdominal wall.
What is potters sequence, what is the cause?
Severe Oligohydramnios → Pulmonary hypoplasia (no space/minmal amino acids) Developemental abnormality: Limb deformity, epicanthic folds, flattened face, low set ears
20 weeks >20weeks - fetal urine produces amniotic fluid.
- Bilateral renal agenesis or
- atresia of urether or uretha
- PPROM
- Ueteroplacental insufficiency
Potters sequence diagnosis:
Prognosis
- USS during 2nd trimester
Often stillbirth or dies in first days of life
When are where do the genital/gonadal ridges form?
Week 4, thickened area of mesothelium on medial side of mesonephros - remains indifferent until week 7
How and when to the primordial germ cells enter the genital ridge?
From yolk sac migrate along the dorsal mesentery invading the ridge at week 6
What gene on the short arm of the Y chromosome determines the differentiation of the gonads?
SRY gene sex determining region
At how many weeks is testosterone produced & where from?
Leydig cells
From week 7
How does the oogine become surround in epithelial cells that become the follicular cells?
At 4 months surface epithelium form cords that surround the germ cells and separate.
What does the mesonephric duct (wolffian) form in the male?
Duct of epididymis
Ductus deferens
Ejaculatory duct and seminal visible
Ureter/renal pelvis/calyces and collecting tubes
What does the paramesonephric duct from in females?
Uterine tube, uterus, hydatid
What is a gartners cyst?
Persisting mesonephric duct- develops as cyst in uterus or vagina
Explain the indifferent stage of the external genitalia
At week 3, cloacal membrane fold & unit in midline forming the genital tubercle divided into anterior urethral folds and posterior anal fold.
Either side of urethral folds a swelling becomes apparent - genital swelling (form scrotal swelling in men or labia majora in females)
What happens to the external genitalia in the presence of androgens?
The genital tubercle elongates (forming the phallus) and the urethral grove closes forming the penile urethra.
The labioscrotal swelling fuse to form the scrotum
What is androgen insensitivity hormone?
XY chromosome but due to sensitivity to testosterone, external gentialia develop as female, testes do not descend (cyptochordism) but tests still produce anti-mullairan hormone so the uterus/uterine tubes do not develo, vagina ends in blind pouch. No mesus.
X linked recessive
What is hypospadias?
Failure of fusion of urethral folds
1/300 males
What is epispadias
What other condition is it associated with?
Genital tubercule developers in region of urorectal septum.
Urethra on the dorsal of penis
1/30000
Associated with exstrophy of the bladder
Describe the descent of the testes
Testes descend with the degeneration of the mesonephros, the follow the gebernaculum to the anterior abdominal wall, by week 12 reaches the inguinal canal and by week 28 passes through & reaches the scrotum by week 33.
As the the testes descend from the abdominal cavity into the testes it forms an extension called the processes vaginalis which is obliterated at birth.
What is the origin of the vagina?
Urogenital sinus - sinovaginal bulbs → failure to form causes absence of vagina/uterus
What is cryptochidism?
Incidence
Managemnt
undescended testes
30% premature infants, 3-4% term
Most cases they descend by the end of the 1st year. If stay in the abdomen at end of 1st year - likely sterility
Often caused by deficient testosterone
