Group 1 - Set 3/4 - Embryology of Urogenital system COMPLETE ***

Question 1

Embryology: Describe how the cloaca is converted into 2 separate openings in mammals (4)

Answer 1

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

Question 2

Embryology: What are the 3 divisions of mesoderm?
- What does it form?

Answer 2

paraxial mesoderm
intermediate mesoderm
lateral plate mesoderm

everything apart from the skin and lining of the gut

Question 3

Intermediate Mesoderm: What 3 bilaterally symmetrical sections does it divide into from cranial to caudal?

Answer 3

pronephros
mesonephros
metanephros

Question 4

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?

Answer 4

pronephros
it regresses

Question 5

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?

Answer 5

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

Question 6

When the Mesonephric ducts connect with the cloaca, what has happened?
- Where does the urine flow and why?

Answer 6

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

Question 7

While the Mesonephros is developing and the ducts connecting to the cloaca, what is happening in the background?
- What will these ultimately become?

Answer 7

metanephric masses are growing

mammalian kidneys

Question 8

In fish and amphibians, how is the development of Mesonephros different?

Answer 8

the mesonephros does not regress and remains as the functional kidney

Question 9

In Mammals, when the mesonephros regresses, what does it become in the embryo?

Answer 9

the gonads and adrenal cortex

Question 10

The Metanephric ducts invade the Metanephric masses.
- What does this stimulate?
- at the same time, what has the Urorectal septum done?

Answer 10

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

Question 11

Describe what happens as the mesonephros is degrading and the metanephros masses are growing

Answer 11

paired metanephric ducts grow out of the mesonephric ducts towards the metanephric masses

Question 12

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?

Answer 12

the ductus deferens

a male

Question 13

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 in females?
- Where do they form?
- Do these form in males to?

Answer 13

paramesonephric ducts

as grooves sinking into the mesoderm of the abdominal wall

yes but they will eventually regress

Question 14

To become a female, what has to happen? (2)

Answer 14

the paramesonephric ducts approach but do not fuse with the gonads

the mesonephric ducts within the gonads regress

Question 15

In the female, what do the caudal ends of the paramesonephric ducts do?
- What does this create?
- then what does the caudal end do?

Answer 15

they fuse to different extents

a uterus

it induces a bud from the endoderm of the cloaca and forms a cervix and vagina

Question 16

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?

Answer 16

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

Question 17

Developmental Defects: What happens with ectopic ureters?
- What does this lead to?

Answer 17

one or both furthers enter the urethra downstream of the bladder sphincter

urinary incontinence

Question 18

Developmental Defects: Free Martins Heifer
- When does this happen?
- Why does it produce a sterile heifer? (4)
- Which hormones might the heifer produce? (2)
- What behaviour is the CNS programmed to exhibit?

Answer 18

when a heifer is born twin to a bull

because a common blood supply between the twins allows XY germ cells to migrate to female ovaries
and the female is exposed to testosterone
so the paramesonephric ducts dont develop completely
and the ovaries dont develop a full complement of XX germ cells

testosterone
androstenedione

male behaviour

Question 19

Developmental Defects: Free Martins Heifer
- What visible gross abnormalities would you see? (3)
- What abnormalities would you feel on rectal palpation? (2)

Answer 19

enlarged clitoris
under developed vulva
long hairs near vulva

small or absent uterus
small ovaries