Development of the Placenta

Question 1

What does the myometrium do during the follicular phase of the menstrual cycle?

Answer 1

Sends off artery branches into the endometrium. As they grow they coil into a spiral (known as spiral arteries).

Question 2

What are the finger-like projections of the syncytiotrophoblast called?

Answer 2

Chorionic villi.

Question 3

What do chorionic villi contain?

Answer 3

Foetal blood vessels.

Question 4

Describe the structure of the chorionic villi nearest to the connecting stalk of the developing embryo (2). What is this area called?

Answer 4

1. Very vascular
2. Contain mesoderm

Called chorion frondosum

Question 5

What does the chorion frondosum become?

Answer 5

Placenta

Question 6

What does the connecting stalk become?

Answer 6

Umbilical cord

Question 7

When is placental development completed?

Answer 7

~10 weeks gestation

Question 8

How do lacunae form?

Answer 8

Trophoblast invasion of the endometrium sends signals to the spiral arteries in that area, reducing their vascular resistance and making them more fragile. The blood flow to these arteries increases, and eventually they break down, leaving pools of blood called lacunae (lakes)

Question 9

When do lacunae form?

Answer 9

~20 weeks gestation

Question 10

Describe the relationship between lacunae and chorionic villi.

Answer 10

Lacunae surround the chorionic villi, separated by the placental membrane. Oxygen, carbon dioxide and other substances can diffuse across the placental membrane between the maternal and fetal blood.

Question 11

What happens when the process of forming lacunae is inadequate?

Answer 11

Pre-eclampsia.

Question 12

What causes pre-eclampsia?

Answer 12

High vascular resistance in spiral arteries leading to sharp rise in maternal blood pressure.