Embryology - Development of Cloaca Flashcards
What is an allantois?
Diverticulum form the endoderm of the yolk sac.
What occurs at the caudal end of the embryo?
The hindgut and allantoid meet in a common cavity - cloaca.
How is the cloaca bound?
Dismally by the cloacal membrane.
What grows from the dorsal wall of the allantois?
Urorectal septum - grows downwards to meet the cloacal membrane.
What happens when the urorectal septum meets the cloacal membrane?
It divides the cloaca and membrane into two.
What are the two areas that the cloaca and membrane are divided into?
- Front:
- Urogenital sinus.
- Urogenital membrane. - Back:
- Anorectal canal.
- Anal membrane.
Where does the anorectum and anal membrane lie?
Small ectodermal depression - proctodeum.
What does the dorsal part of the sinus become?
- Rectum.
- Anal canal.
How many parts does the Urogenital sinus (endoderm) have?
Three parts.
What is the uppermost part of the Urogenital sinus?
Vesicular (veiscourethral) part - largest part.
What does the vesicourethral part form?
- Most of the bladder epithelium.
- Female urethra.
What does surrounding mesoderm in the vesicourethral part form?
Muscle and connective tissue of the bladder.
How is the urethra formed in males?
The lower part of the urogenital sinus becomes the proximal prostatic urethra as far as the openings of the ejaculatory ducts and prostatic utricle.
Where does the mesopnephric duct open up?
Into the lower part of the vesicourethral part.
Where/how does the ureter form?
As a bud form the mesonephric duct. THe duct and the ureter grow apart and open separately into the sinus, the ureter opens at a higher level than the duct.
What happens at the lower end of the mesonephric duct?
The duct and the ureter become incorporated into the developing bladder to form the trigone.
What does the lowest part of the mesonephric duct form?
The ejaculatory opening in the prostatic urethra.
What is the middle part of the urogenital sinus?
Pelvic part.
What does the pelvic part of the urogenital sinus form?
- Rest of prostatic urethra.
- Membranous urethra.
- Prostate.
- Epithelium of the vagina in females (derived principally from the paramesonephric ducts).
What does contributing mesoderm isn’t he pelvic part of the urogenital sinus contribute to?
Fibromuscular stroma.
What is the lowest part of the urogenital sinus?
Phallic part.
What does the phallic part of the urogenital sinus form?
- Dorsal part of the penis.
- Penile urethra.
- Vestibule of the vagina.
What is a genital tubercle?
It is a midline mesodermal swelling at the front of the urogenital membrane.
What does the genital tubercle become?
- Clitoris.
- Glans penis.
What are the urogenital folds?
These are at the back of the genital tubercle that lay each side.
What happens to the urogenital folds in females?
They remain separate to form the labia minora.
What happens to the urogenital folds in males?
They unite at the back to form the midline raphe of the scrotum.
What are genital (labioscrotal) swellings?
These are swellings which develop lateral to the urogenital folds.
What do genital swellings form?
- The rest of the scrotum.
- Labia majors in females.
What do the front parts of the urogenital folds form in males?
They unite from the scrotum forwards as the ventral part of the penis and penile urethra.
