Embryology Flashcards
What does the urogenital system develop from?
Intermediate mesoderm
What are the 3 sets of structures during kidney development and when are the present?
Pronephros - appears week 3 and regresses by week 4.
Mesonephros - appears week 4 and regresses by week 8
Metanephros - appears week 5 and fully functional by week 11.
What makes up the mesonephros and where does it drain to?
Mesonephric duct and mesonephric tubules.
Drains to cloaca.
Describe formation of the definitive kidney.
Ureteric bud develops as outgrowth from caudal mesonephric duct.
The nephrogenic cord covers this bud and forms the metanephric cap.
Both of these structures form the definitive kidney.
What does the ureteric bud form?
Collecting system
What does the metanephric cap form?
Nephrons
What epithelium lines ducts?
Cuboidal
What epithelium lines tubules?
Columnar
What does the bladder and urethra arise from?
Endoderm
What does the bladder develop from?
Cranial part of UG sinus and caudal parts of mesonephirc duct (trigone).
When do gonads first develop male/female characteristics?
Week 7
When do genital ducts develop?
Weeks 5-6.
What are female and male ducts called respectively?
Female - paramesonephric (Mullerian)
Male - mesonephric (Wolffain)
What happens to mesonephric ducts in males and females?
In males, testosterone causes the formation of ductus deferens, seminal vesicle, ejaculatory duct and epididymis.
In females, duct disappears due to absence of testosterone.
What happens to paramesonephric ducts in males and females?
In males, Sertoli cells produce AMH which causes degeneration.
In females, ducts form funnel-shaped cranial ends that open into the peritoneal cavity. They meet in the midline and go onto form -
Cranial portion - uterine tubes
Caudal portion - uterovaginal primordium (sup vagina and uterus).
Where do primordial germ cells form?
Yolk sac
What causes indifferent gonads to become testes?
SRY acts on somatic cells causing proliferation of sex cords. Leydig cells then produce testosterone and Sertoli cells produce AMH.
Dense connective tissue forms - tunica albuginea - which separates cords from surface epithelium.
What causes indifferent gonads to become ovaries?
Presence of Wnt 4 and absence of SRY.
- Surface epithelium proliferates to form surface of ovary, and PGCs align along cortex and proliferate.
Cloacal folds develop around the cloacal membrane around week 3. What do these form?
Cranial end - folds join to form genital tubercle.
Caudal end - folds are subdivided.
- Those in front - labia minora/ventral aspect of penis
- Those behind - anus
What develop around urethral folds and what do these give rise to?
Genital swellings.
- Become scrotum in males and labia majora in females.
What week does formation of the phallus occur?
Week 9
What week do external genitalia develop male and female characteristics?
Week 12
What does the phallus and genital swellings become in males?
Penis and scrotum
What does the phallus and genital swellings become in females?
Clitoris and labia majora
