3. Placental formation

Question 1

At what spinal level does the ovarian artery arise from the aorta?

Answer 1

L4

Question 2

What does the ovarian artery supply?

Answer 2

Tubes, ovaries, round ligaments and body of uterus

Question 3

What reproductive arteries does the internal iliac give rise to?

Answer 3

Uterine and vaginal

Question 4

What does the uterine artery supply?

Answer 4

The body of the uterus and the cervix

Question 5

Describe the blood supply, to, in and from the placenta? (From mum)

Answer 5

Uterine artery to spiral arteries to endometrial veins to uterine veins.

Question 6

Describe the placental blood supply to, in and from the placenta (baby side).

Answer 6

Umbilical artery (x 2) to chorionic arteries to villus tree to chorionic veins to uterine vein (x1)

Question 7

What do the maternal and baby parts of the placenta arise from?

Answer 7

Mum = decidua from endometrium

Baby = chorion (trophoblast and mesoderm)

Question 8

How do the trophoblast and mesoderm for the placenta?

Answer 8

Trophoblast spits into:
Cytotrophoblast - forms outer layer of the villous tree
Synctiotrophoblasts - forms intervillous space lining

Mesoderm forms villous tree

Question 9

How many spiral arteries are there?

Answer 9

Up to 200

Question 10

How does the trophoblast effects placental blood flow and what are the effects of failure of this?

When does this occur?

Answer 10

Surrounds distal spiral arteries, reducing vasoconstriction. Creates a low pressure vascular system (10mmhg).

Invasion failure = IUGR and PET

Starts around 10w and finishes 16w

Question 11

What size and weight is an average placenta?

Answer 11

20cm diameter and 3cm thick

Around 500g

Question 12

How do we calculate uteroplacental blood flow?

Answer 12

Uterine artery pressure - uterine vein pressure

Divided by

Uterine vascular resistance

Question 13

What factors decrease uteroplacental blood flow?

Answer 13

Decreased by increased uterine venous pressure e.g. IVC compression and valsalva (contractions) and decreased UAP e.g. hypotension and increased vascular resistance e.g. PET, HTN or vasoconstrictors

Question 14

How effective is placental gas exchange compared to the lungs and why?

Answer 14

Less effective than the lungs as wider gap between vessels and blood barrier is tighter.

Question 15

What are the different types of accreta?

Answer 15

Accreta = through decidua to reach muscle, so no line of cleavage

Increta= into muscle

Percreta = through muscle to serosa or surrounding structures

Question 16

Look at diagrams on obs compressed 3.

Answer 16

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