Placenta

Question 1

Where does the embryo receive its early nutrition from?

Answer 1

Diffusion through zona pellucida
Blastocyst fluid
Yolk sac

Question 2

Where does the foetus receive its long term nutrition from?

Answer 2

Maternal circulation (from day 12 - term)

Question 3

Where do ectopic pregnancies most commonly occur?

Answer 3

Uterine tubes

Question 4

What is an ectopic pregnancy?

Answer 4

Implantation outside of the uterine cavity

Question 5

What can ectopic pain be mistaken for?

Answer 5

Appendicitis

Question 6

What is the decidua?

Answer 6

Endometrium once it has undergone changes due to pregnancy hormones

Question 7

What are the 3 layers of the decidua?

Answer 7

Decidua Basalis (under the blastocyst) 
Decidua Capsularis (covering blastocyst) 
Decidua Parietalis (remainder of uterine lining)

Question 8

Which part of the decidua forms the maternal placenta?

Answer 8

Decidua Basalis

Question 9

What are the functions of the placenta?

Answer 9

Endocrine (HCG, progesterone, oestrogen)
Transfer (for nutrition and waste)
Immunity (IgG antibodies able to cross easily)

Question 10

What are the key foetal membranes?

Answer 10

Chorion
Amnion

[But also yolk sacs and allantois]

Question 11

What is the key contents of the umbilical cord?

Answer 11

2 x umbilical arteries
1 x umbilical vein
Surrounded by Wharton’s jelly

Question 12

What should you check when cutting the umbilical cord after birth?

Answer 12

Presence of 2 umbilical arteries - having only one artery could lead to CV defects

Question 13

When do lacunae networks form?

Answer 13

Days 10-12

Question 14

How do lucanae networks form and what is their function?

Answer 14

Fusion of adjacent lacunae to form networks in the syncytiotrophoblast
Maternal spiral arteries and veins open into lacunae and is returned via endometrial veins - nourish the embryo by diffusion

Question 15

How and when do chorionic villi form?

Answer 15

Week 2 = cells from cytotrophoblast grow into syncytiotrophoblast forming primary chorionic villi
From week 3 = extraembyronic mesenchyme grows into primary villi forming secondary villi
Week 3 = blood vessels develop in extraembryonic mesoderm and communicate with the umbilical vessels forming tertiary villi

Question 16

How does placental anchoring occur?

Answer 16

Cytotrophoblast grows through and surrounds syncytiotrophoblast forming a shell with chorionic villi attached (anchoring the villi) - shell attaches to decidua basalis

Question 17

What happens to the placental membrane throughout gestation and what is the clinical relevance of this in post-date pregnancies?

Answer 17

Gets thinner to cope with increasing nutritional demand

Post-date pregnancies may result in placenta not being able to keep up with demand

Question 18

What is placental accreta?

Answer 18

Uncontrolled invasion of the placenta into the myometrium of the uterus - can result in placenta not detaching properly at birth increasing risk of post-partum haemorrhage

Question 19

What is placental percreta?

Answer 19

Most severe form of placental accreta in which the chorionic villi invade the perimetrium of the uterus - can result in placenta not detaching properly at birth significantly increasing risk of post-partum haemorrhage

Question 20

What is placental previa?

Answer 20

Occurs when the placenta lies low in the uterus and partially or completely covers the cervix - increases risk of haemorrhage during late pregnancy, labour or delivery due to risk of placenta separating from the uterus wall as cervix begins to dilate

Question 21

What is placental abruption?

Answer 21

Placental separation from the uterine wall during pregnancy resulting in subplacental haemorrhage

Question 22

What is inadequate placentation?

Answer 22

Failure of normal invasion of trophoblast cells leading to maladaptation of maternal spiral arterioles and poor uteroplacental blood flow (pre-eclampsia)

Question 23

What is the embryological remnant of the allantois?

Answer 23

Urachus (on bladder)

Question 24

What makes up the chorion membrane?

Answer 24

Syncytiotrophoblast
Cytotrophoblast
Extraembryonic mesoderm