Week 1 - Reproduction: Embryology Flashcards
Embryology: Where does the yolk sac connect to?
- What does it become?
- What does the Allantoic sac connect to?
- What does it become?
the midgut
the choriovitelline placenta
the bladder which forms as a result of the growth of the urorectal septum
the chorioallantoic placenta
Embryology: Describe how the cloaca is converted into 2 separate openings in mammals (4)
the urorectal septum grows caudally towards the cloacal membrane
this separates the cloaca into 2 separate openings
one opening is for the gastrointestinal tract
one opening is for the urinary tract
Embryology: What are the 3 divisions of mesoderm?
- What does it form?
paraxial mesoderm
intermediate mesoderm
lateral plate mesoderm
everything apart from the skin and lining of the gut
Embryology: What does the Paraxial mesoderm become? (2)
- What does the Intermediate mesoderm become? (4)
dermis
limbs
nephros
urinary ducts
adrenal cortex
sex cords of the gonads
Intermediate Mesoderm: What 3 bilaterally symmetrical sections does it divide into from cranial to caudal?
pronephros
mesonephros
metanephros
Mammalian Embryo: After the Pronephros atrophies, what happens?
- What does it do as the embryo grows?
- Describe the structure of the Mesonephros
- What do they function as?
- How do the mesonephric ducts form?
- What do they connect to?
- Where do they grow to?
the mesonepros develops
it regresses
it consists of segmental mesonephric tubules draining into mesonephric ducts
a kidney
spontaneously in the mesoderm
they connect to the segmental mesonephric tubules inside the mesonephros
they grow towards the cloaca
Mammalian Embryo: The nephros develop cranially to caudally, as a wave of development down the embryo as it grows.
What is the first Nephros to form?
- What does it eventually do?
pronephros
it regresses
When the Mesonephric ducts connect with the cloaca, what has happened?
- Where does the urine flow and why?
the urine produced in the mesonephros can now drain into the cloaca
down the allantois into the allantoic cavity as the cloacal membrane is still intact
While the Mesonephros is developing and the ducts connecting to the cloaca, what is happening in the background?
- What will these ultimately become?
metanephric masses are growing
mammalian kidneys
In fish and amphibians, how is the development of Mesonephros different?
the mesonephros does not regress and remains as the functional kidney
In Mammals, when the mesonephros regresses, what does it become in the embryo?
the gonads and adrenal cortex
The Metanephric ducts invade the Metanephric masses.
- What does this stimulate?
- at the same time, what has the Urorectal septum done?
the formation of the nephrons and blood supply in the metanephric masses
it has divided the cloaca into an exit for the go tract and a common urogenital opening
The metanephric masses are growing in the embryo.
- What is happening at this time to the mesonephros and how?
- What happens to the cranial end of the Mesonephros?
degeneration by apoptosis
it becomes the gonads and adrenal cortex
Describe what happens as the mesonephros is degrading and the metanephros masses are growing
paired metanephric ducts grow out of the mesonephric ducts towards the metanephric masses
The mesonephros has now fully degraded and left behind gonads and adrenal cortex.
- In males, what have the mesonephric ducts become?
- Now what do we have?
the ductus deferens
a male
Backtrack to where the Mesonephros is still active and the metanephric ducts have just connected with the Metanephric masses.
- What else is forming alongside the Mesonephric ducts?
- Where do they form?
- Do these form in males to?
paramesonephric ducts
as grooves sinking into the mesoderm of the abdominal wall
yes but they will eventually regress
Describe the development of the paramesonephric ducts
they become elongated
they grow towards the gonads and the cloacal regions
To become a female, what has to happen? (2)
the paramesonephric ducts approach but do not fuse with the gonads
the mesonephric ducts within the gonads regress
In the female, what do the caudal ends of the paramesonephric ducts do?
- What does this create?
- then what does the caudal end do?
they fuse to different extents
a uterus
it induces a bud from the endoderm of the cloaca and forms a cervix and vagina
Females: What happens to the ovaries once the uterine horns, uterus, cervix and vagina have been formed?
- is there a distinct boundary between the cervix and vagina?
- Where is the vagina located?
- Where is the vestibule located?
they migrate caudally to a post renal position
no
from the cervix to the entry of the urethra
from the urethra to the vulva
Kidney Formation: After the metanephric ducts invade the metanephric masses and stimulate the formation of nephrons and a blood supply:
- What does the blood supply form?
- What does the mesoderm form? (4)
- What do the Metanephric ducts form? (3)
the glomerular tufts
Bowmans capsule
proximal convoluted tubule
loops of henle
distal convoluted tubule
collecting ducts
renal pelvis
ureter
Formation of final positions of Ureters and Ductus Deferens in males:
- What 2 embryological structures are attached to the bladder?
- What does the Mesonephric duct become?
- What does the Metanephric duct become?
mesonephric ducts and metanephric ducts
the ductus deferens
the ureters
Formation of final positions of Ureters and Ductus Deferens in males:
- describe the path of the Ductus deferens as it descends towards the scrotum
- What happens as the mesonephric ducts (ductus deferens) collapse over the bladder as they loop over?
- Do we get this in females too?
- How is the trigone tissue different to the bladder wall tissue?
- How is the trigone of the bladder clinically relevant?
it loops over the ureters as the testes descend
they leave a trail of mesoderm tissue creating the trigone of the bladder
yes but it is smaller as the mesonephric ducts regress
the trigone is derived from mesoderm but the bladder is derived from endoderm
bladder neoplasia starts in the trigone
Testicular development:
- What happens first in the Testis in the developing male embryo? (3)
undifferentiated sex cords align against the rete tubules
the rate tubules are a network of ducts which ultimately connect to seminiferous tubules to the efferent ducts
at this point the mesonephric tubules have not interconnected with rete tubules
Testicular development: What happens second in the Testis in the developing male embryo?
the rete tubules and mesonephric tubules interconnect to provide a continuous pathway from the undifferentiated sex cords and the mesonephric duct
Testicular development: What happens finally in the Testis in the developing male embryo? (2)
undifferentiated sex cords become seminiferous tubules
the mesonephric duct develops into the epididymis and ductus deferens
