Placenta

Question 1

At what day does implantation occur?

Answer 1

7

Question 2

What are the contents of the umbilical cord?

Answer 2

2 arteries
1 vein
Wharton’s jelly
Amnion cover

Question 3

What are the fetal membranes?

Answer 3

Chorion
Amnion
Yolk sac
Allantois

Question 4

Where does early nutrition of the embryo come from?

Answer 4

Simple diffusion through the zona pellucida

Blastocyst fluid and yolk sac

Question 5

What day does long term nutrition start?

Answer 5

Day 12 placenta takes over nutritional supply

Question 6

What day does the blastocyst attach and then implant to the endometrium?

Answer 6

Attaches at day 6-7

Implantation at days 12-13

Question 7

Where is the blastocyst fertilised and then implanted?

Answer 7

Ampulla of the uterine tube

Fundus of the uterus (uterine cavity)

Question 8

What triggers decidualisation and what day does it occur?

Answer 8

Day 7
Blastocyst implantation on endometrial lining and PROGESTERONE
Uterine cells become decidual cells when they accumulate lipid and glycogen

Question 9

What changes occur during decidualisation?

Answer 9

Trophoblast differentiates into cut-trophoblast and syncitiotrophoblast
Uterine lining changes epithelium to become decidual cells

Question 10

What are the 3 decidual layers?

Answer 10

Decidua basalis (maternal placenta)
Decidua capsularis (covers blastocyst)
Decidua parietalis (covers remainder of uterine cavity)

Question 11

What condition does ectopic pain mimic?

Answer 11

Appendicitis

Question 12

What are some ectopic implantation sites?

Answer 12

Anywhere within peritoneal cavity with a blood supply

95% within uterine tubes

Question 13

What are the functions of the placenta?

Answer 13

Hormones (hCG, progesterone, oestrogen)
Immunity (passive, IgG)
Nutrition (O2, CO2, glucose)

Question 14

What are lacuna networks, what day do they appear?

Answer 14

Days 10-12
Open spaces in the syncitiotrophoblast (= lacunae that fill with maternal blood)
Adjacent lacunae fuse
Maternal spiral arteries open into them

Question 15

What vein does maternal blood return in?

Answer 15

Endometrial vein

Question 16

Outline primary, secondary and tertiary chorionic villi

Answer 16

Cells from cytotrophoblast invade syncitiotrophoblast to form primary chorionic villi

Extraembryonic mesenchyme grows into primary villi to form secondary chorionic villi

Blood vessels develop in the extraembryonic mesoderm providing communication with umbilical artery and vein

Question 17

At what week is foetal blood present?

Answer 17

By the end of week 3 (once tertiary chorionic villi are formed)

Question 18

What’s the deal with foetal and maternal circulation and blood flow around the placenta?

Answer 18

Branched chorionic villi bathed in maternal blood of placenta essential for embryonic survival

Foetal and maternal circulations never mix, are just in very close contact

Question 19

Which zone of the uterus does the placenta sit in?

Answer 19

Junctional zone

Question 20

What are the components of the foeto-maternal membrane?

Answer 20

Maternal blood -> Syncitiotrophoblast -> Cytotrophoblast -> Foetal capillaries

Question 21

Why does the placenta thin throughout pregnancy?

Answer 21

Majorly from week 22/38
Majority of cut-trophoblast layer lost
Surface area increases and thins to meet increased metabolic demands of foetus

Question 22

What are some placental dysfunctions?

Answer 22

Transport unwanted substances/pathogens
Implantation site (ectopic/previa)
Abruption (revealed, concealed, both)
Uncontrolled invasion (accreta/percreta)
Inadequate blood flow

Question 23

What’s accreta and percreta?

Answer 23

When placenta implants at wrong location/too deeply

Can go partly through myometrium (accreta) or all the way through it (percreta)

Question 24

What’s placenta previa?

Answer 24

Insertion of the placenta low down in the uterine cavity - it covers internal os = patient presents with bleeding

Question 25

What could result in inadequate blood flow to the placenta?

Answer 25

Pre-eclampsia = failure of normal invasion of trophoblast cells leading to maladaptation of maternal spiral arteries

Impairment: maternal vascular disease, post gestational age
Mechanical: IVC compression
Volume: maternal haemorrhage or hydration