Embryology Flashcards
What happens in weeks 1 and 2 of gestation?
Blastocyst forming and implanting in the uterus, starts to form 3-layered embryo
What happens in week 3 of gestation?
Gastrulation
Neurulation
Somite formation
What happens in weeks 4-8 of gestation?
Organogenetic period
What happens from week 9 onwards of gestation?
Maturation of organ systems
What is the timeline of reproductive system organogenesis?
Reproductive system organogenesis occurs beyond 8 weeks and beyond the post-natal period, it is not complete when the child is born
What are the 3 initial sets of kidneys that develop in gestation?
Pronephros - first rudimentary kidney
Mesonephros - briefly functional kidney with ducts and primitive urethra
Metanephros - functional, in pelvic region
What does the cloaca divide to form?
Rectum and urogenital sinus
What does the mesonephric duct drain into?
Urogenital sinus
What does the urogenital sinus form later in development?
Urinary bladder, caudal end forms urethra
The epithelium of the mesonephros invaginates to form
a tube which then becomes the paramesonephric duct
What does the paramesonephric duct develop lateral to in development?
Developing gonads and mesonephric duct
Where does the cranial end of the paramesonephric duct open?
Into the peritoneal cavity
What happens to the mesonephros at week 6 of development?
Forms a long ovoid structure in association with the thoracic and upper lumbar vertebrae
The medial part of the mesonephric ridge thickens to form
a genital/gonadal ridge
At week 6, germ cells migrate from the yolk sax via the
dorsal mesentery, and embed into the primitive sex cords
What are the primitive sex cords formed from?
Mesenchyme of genital ridges
What is the indifferent gonad?
A gonad that has not developed into a definitive ovary or testis, there is no migration of germ cells at this stage and so no true gonads
What primitive structures are needed to form the reproductive system?
Indifferent gonad Mesonephric duct (disappears in females) Paramesonephric duct (disappears in males)
What happens to the indifferent gonad, mesonephric duct, paramesonephric duct and urogenital sinus in males?
Gonad forms testis
Mesonephric duct develops into the epididymis, vas deferens and seminal vesicle
Paramesonephric duct degenerates
Urogenital sinus forms bladder, urethra and prostate
In the early stages of development, what is the only difference between the male and female embryo?
XY compared to XX
What makes the indifferent gonad develop into a testis?
SRY on the sex-determining region of the Y chromosome encodes a protein called TDF (testis determining factor) which makes indifferent gonad develop into a testis
What cells express the SRY gene?
Primordial sex cells within he sex cords of the indifferent gonad
What do Sertoli cells secrete?
Mullerian Inhibiting Substance (MIS)
What does MIS cause?
Paramesonephric duct to degenerate so only mesonephric duct remains
Also transorms mesenchymal cells between sex cords into Leydig cells which produce testosterone
