13 Placenta

Question 1

Outline when and how implantation of the blastocyst occurs?

Answer 1

Day 6- pregnancy

• Trophoblast cells interact with endometrial lining
• Embedded in lining- interact with vasculature and glands

Question 2

Where should/does implantation usually occur?

Answer 2

Superior body of uterus

(if implantation over previous c-section scars= not usually viable)

Question 3

What is placenta praevia?

Answer 3

When implantation occurs occurs over internal os.

Question 4

Implantation can also be too deep or to shallow and have complications. What is it called if implantation if too deep?

Answer 4

Placenta accreta

Question 5

Which layers of the embryo does the placenta develop from?

Answer 5

Trophoblast (outer cell mass)

• Syncytiotrophoblast
• Cytotrophoblast

Question 6

How does the placenta develop from the amniotic membrane and the chorionic membrane.

Answer 6

Question 7

The following diagram shows a chorionic villus. The maternal blood vessels surround these villi, allowing exchange to occur but the blood never mixes. What forms the barrier between the 2 blood supplies?

Answer 7

Single layer of trophoblast

Question 8

How does the thickness of the barrier between the maternal and fetal circulations change as the pregnancy progresses?

Answer 8

At first- thick- cytotrophoblast and syncytiotrophoblast

Then cytotrophoblast cells lost

Question 9

What is the decidua?

Answer 9

Cells of endometrium- specialised to modulate degree of invasion of conceptus

Decidual reaction

Question 10

What can happen if the conceptus implants where there is no decidua? (eg tubal ectopic pregnancy)

Answer 10

No inhibition of decidualistation - no control over extent of invasion

Question 11

What can happen if implantation occurs in the correct place but the decidual reaction is suboptimal?

Answer 11

• Miscarriage
• Infertility
• Placenta insufficiency–> pre-eclampsia

Question 12

Via which vessels are waste products from the fetus brought to the chorionic villi?

Answer 12

Question 13

Outline the functions of the placenta

Answer 13

Question 14

What is a teratogen?

Answer 14

An agent or factor which causes malformation of an embryo

Question 15

What is Rhesus disease?

Answer 15

Blood group incompatibility

Antibodies from maternal blood cross into fetal circulation- attack fetal blood cells

Question 16

When in pregnancy do teratogens have their greatest effect?

Answer 16

Early pregnancy

3-8 weeks

Question 17

What might the presence of hCG in males indicate?

Answer 17

Testicular malignancy

Question 18

Why are IgG concentrations higher in fetal plasma than in maternal circulation?

Answer 18

IgG is preferentially taken up- receptor mediated pinocytosis

Question 19

Summary of transport from maternal circulation to fetal circulation:

Answer 19

Question 20

Give some examples of teratogens:

Answer 20