Foetal Growth and Placentation

Question 1

Describe early embryo nutrition with a word.

Answer 1

histiotrophic

Question 2

Early embryo is reliant on what for nutrition?

Answer 2

uterine gland secretions and breakdown of endometrial tissues

Question 3

At the start of the 2nd trimester, embryo switches from histiotrophic to ______ support.

Answer 3

haemotrophic

Question 4

How is haemotrophic support achieved in humans?

Answer 4

through a haemochorial-type placenta where maternal blood directly contacts the fetal membranes

Question 5

Define chorion.

Answer 5

outermost membrane surrounding an embryo

Question 6

What is the connecting stalk?

Answer 6

links embryo to chorion

Question 7

What are trophoblastic lacunae

Answer 7

Large spaces filled with maternal blood formed by breakdown of maternal capillaries and uterine glands
Become intervillous spaces aka maternal blood spaces

Question 8

Define amnion.

Answer 8

innermost membrane that encloses the embryo

Question 9

Define foetal membranes.

Answer 9

extraembryonic tissues that form a tough but flexible sac encapsulates the fetus and forms the basis of the maternal-fetal interface

Question 10

The amnion arises from?

Answer 10

epiblast

Question 11

The amnion goes on to form?

Answer 11

closed, avascular sac with developing embryo at one end

Question 12

Amniotic sac is filled with?

Answer 12

amniotic fluid

Question 13

Amniotic fluid is secreted from what week?

Answer 13

5th week

Question 14

Functions of amniotic sac

Answer 14

encapsulates and protects the embryo

Question 15

The chorion arises from?

Answer 15

yolk sac derivatives and the trophoblast

Question 16

Is the chorion avascular or highly vascularised?

Answer 16

highly vascularised

Question 17

The chorion gives rise to?

Answer 17

chorionic villi

Question 18

What are chorionic villi?

Answer 18

outgrowths of cytotrophoblast from the chorion that form the basis of the fetal side of the placenta

Question 19

Amniotic sac is formed of what two layers?

Answer 19

amnion on the inside

chorion on the outside

Question 20

What is the allantois?

Answer 20

outgrowth of the yolk sac

Question 21

Allantois grows along?

Answer 21

connecting stalk from embryo to chorion

Question 22

Allantois goes on to?

Answer 22

becomes coated in mesoderm

vascularises to form umbilical cord

Question 23

Primary chorionic villi

Answer 23

Cytotrophoblast forms
finger-like projections 
through 
syncitiotrophoblast layer
Into maternal
endometrium

Question 24

Function of chorionic villi

Answer 24

provide substantial surface area for exchange

Question 25

List the three phases of chorionic villi development.

Answer 25

primary secondary tertiary

Question 26

primary phase of chorionic development

Answer 26

outgrowth of the cytotrophoblast and branching of these extensions

Question 27

secondary phase of chorionic development

Answer 27

growth of the fetal mesoderm into the primary villi

Question 28

tertiary phase of chorionic development

Answer 28

growth of the umbilical artery and umbilical vein into the villus mesoderm, providing vasculature.

Question 29

Maternal blood supply to the endometrium

Answer 29

Uterine artery branches > network of arcuate arteries > radial arteries > basal arteries form spiral arteries during menstrual cycle endometrial thickening

Question 30

Spiral artery remodelling

Answer 30

Extra-villus trophoblast (EVT) cells coating the villi invade down into the maternal spiral arteries, forming endovascular EVT. Endothelium and smooth muscle is broken down – EVT coats inside of vessels

Question 31

How does the foetus get oxygen?

Answer 31

across placenta via diffusion (high maternal O2 tension, low fetal O2 tension)

Question 32

How does the foetus get glucose?

Answer 32

facilitated diffusion by transporters on maternal side and fetal trophoblast cells

Question 33

How does the foetus get water?

Answer 33

placenta main site of exchange, though some crosses amnion-chorion. Majority by diffusion, though some local hydrostatic gradients

Question 34

How does the foetus get electrolytes?

Answer 34

large traffic of sodium and other electrolytes across the placenta – combination of diffusion and active energy-dependent co-transport

Question 35

How does the foetus get calcium?

Answer 35

actively transported against a concentration gradient by magnesium ATPase calcium pump.

Question 36

How does the foetus get amino acids?

Answer 36

reduced maternal urea excretion and active transport of amino acids to foetus

Question 37

Maternal changes for maternal-foetal oxygen exchange

Answer 37

^CO 30% in 1st trimester, peripheral resistance decreases 30%, ^blood vol by 40%, ^ pulmonary ventilation 40%

Question 38

Compare O2 content and saturation of foetal and maternal blood.

Answer 38

similar

Question 39

Which has a greater affinity for O2: maternal haemoglobin or foetal haemoglobin?

Answer 39

foetal haemoglobin