Embryology Flashcards
(48 cards)
What occurs in gastrulation
The embryo forms 3 layers
Called the trilaminar disc
When does gastrulation occur
Week 3 of gestation
Where is the urogenital system derived from
The intermediate mesoderm
How are the endoderm and mesoderm formed
Invagination of epiblast cells through the primitive streak
How does cranial-caudal folding affect the embryo
It rolls up like a scroll from each end to give the foetal position
Describe the function of the pronephros, mesonephros and metanephros
The pronephric system will eventually disappear – doesn’t function in humans
Mesonephros is not the end kidney but does have some functional capability in the foetus – some urine production
Metanephric system is the end kidney
Where do the excretory ducts of the forming UG system enter
They join with the cloaca to eventually form an output
Which cells will go on to form gametes
Primordial germ cells
Describe the progression of the primordial germ cells
They form in the yok sac
They work their way into the embryo into the developing gonads (intermediate mesoderm)
When they get in, they stimulate epithelium to start proliferating – forms a gonadal/genital ridge
The proliferating epithelium will form somatic support cells which envelop to the germ cells
These support cells will eventually become the follicular cells or Sertoli cells
Which two ducts form the urogenital system
Mesonephric (Wollfian) duct
Paramesonephric (Mullerian) duct
Where is the mesonephric duct found
Connects to the posterior wall of the urogenital sinus and the cloaca
Joins the paramesonephric duct at the urogenital sinus
Where is the paramesonephric duct found
It is blindly open at the top and opens into the peritoneal cavity
Joins the mesonephric duct at the urogenital sinus at the caudal end of the foetus
When does sexual differentiation occur
From week 7 of gestation onwards
What triggers the differentiation into a male
The presence of the SRY protein transcription factor
This is the sex determining region of the Y chromosome
Describe the effect of SRY on the early gonads
Triggers the somatic support cells to become Sertoli cells and they form medullary cords
These cords engulf the PGCs
Rete testis connect the mesonephric tubules to the testis cords
What happens to the paramesonephric duct in males
It disappears
Sertoli cells secrete anti-Mullerian hormone to cause the degeneration of the paramesonephric duct
How is testosterone production started in the early male
The Sertoli cells stimulate the formation of Leydig cells which secrete testosterone
What is the role of testosterone in the developing male gonads
influences the mesonephric duct to form the structures of the male repro system – epididymis , vas deferens etc
Dihydrotestosterone (DHT) is more potent and stimulates formation of external genitalia
What is persistent Mullerian duct syndrome
When part of the female reproductive tract is present in a biological male
Due to a failure of the anti-Mullerian hormone or its receptors
The paramesonephric duct doesn’t regress
What is cryptorchidism
Failure of descent of one or both testes
Where do the testes originate
Level of T10 on the abdominal wall
How do the testes move down to the scrotum
Tissue called the gubernaculum shortens and pulls the testes down and through the body wall
Should be in scrotum by birth - sitting high up
What is the vaginal process in men and its significance
Vaginal process is a small pocket in front of the descending testes
It should close off and form a space that allows for testicular movement
If it stays open you are at increased risk of inguinal hernias
How do the seminal vesicles develop
They are outpouchings of the mesonephric ducts
