Placentation

Question 1

How is early embryo nutrition given?

Answer 1

Histiotrophic:

reliant on uterine gland secretions and breakdown of endometrial tissues

Question 2

Why is embryo fetal growth during the first trimester limited?

Answer 2

Due to the histiotrophic nature of nutrition

Question 3

At the start of the 2nd trimester what nutrition is used?

Answer 3

Haemotrophic support:

start to derive nutrients from maternal blood through haemochorial type placenta * meaning maternal blood is directly in contact with fetal membranes and this is why the switch occurs from histio to haemotrophic

Question 4

What does the amnion do? (inner fetal membrane)

Answer 4

derivative of epiblast that does not become a part of the fetus

but rather becomes the amniotic cavity and then amniotic sac

secretes amniotic fluid from 5th week - this is how the fluid filled sac is made

Question 5

What is the connecting stalk?

Answer 5

Links developing embryo unit to the chorion

Question 6

What are trophoblastic lucaenea?

Answer 6

large spaces full of maternal blood made by breakdown of her capillaries and uterine gland

become intervillous aka maternal blood spaces *capillaries join and become long and continuous

Question 7

What are fetal membranes?

Answer 7

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

Question 8

What is the chorion? (outer fetal membrane)

Answer 8

made from yolk sac and trophoblast

highly vascularised

gives rise to chorionic villi - outgrowths of cytotrophoblast from chorion that forms basis of the fetal side of the placenta

Question 9

What is the allantois?

Answer 9

Outgrowth of the yolk sac

grows along the connecting stalk from embryo to chorion

becomes coated in mesoderm and vascularises to form the umbilical cord

Question 10

How is the amniotic sac made with both fetal membranes involved?

Answer 10

Expansion of the sac by fluid accumulation pushes the amnion into contact with the chorion = fusion = amniotic sac

so it has two laters, amnion on inside and chorion on outside

Question 11

What are primary chorionic villi?

Answer 11

cytotrophoblast finger like projection through the syncitiotrophoblast layer into maternal endometrium

Question 12

What is the purpose of the chorionic villi?

Answer 12

substantial SA for exchange of gases and nutrtients

these projections undergo branching

Question 13

What are the three phases of chorionic villi development?

Answer 13

primary :outgrowth of the cytotrophoblast and branching of these extensions

secondary: : growth of the fetal mesoderm into the primary villi
tertiary: growth of the umbilical artery and umbilical vein into the villus mesoderm, providing vasculature.
* image on slide 8

Question 14

How do the villi change from early pregnancy to late pregnancy?

Answer 14

early : 150-200µm diameter, approx. 10µm trophoblast thickness between capillaries and maternal blood

late : : villi thin to 40µm, vessels move within villi to leave only 1-2µm trophoblast separation from maternal blood.

Question 15

What does the convulation and dilated of the villi allow?

Answer 15

Slow blood flow in vessels for better exchange

Question 16

Describe the maternal blood supply to the endometrium?

Answer 16

uterine artery branches –> arcuate arteries (uterine will fuse with ovarian)

arcuate –> radial arteries

radial arteries –> basal arteries which from spiral arteries during menstrual cycle endometrial thickening * these are lost if implantion does not occur

Question 17

WHat do extra villus trophoblast cells do? (EVT cells)

Answer 17

Coat villus and invade down into maternal spiral arteries to form

Endovascular EVT cells

made to replace the broken down endothelium and smooth muscle of the mother

Question 18

What does conversion mean?

Answer 18

spiral artery re-modelling

The process of EVT coating the spiral arteries

affect: turns the spiral artery into low pressure, high capacity conduit for maternal blood flow

Question 19

What nutrients are being exchanged across the placenta?

Answer 19

O2
Glucose
Water
Electrolytes
Calcium
Amino acids

Question 20

How is calcium transported across placenta?

Answer 20

active transport by Mg ATPase calcium pump

Question 21

How is Oxygen transported across placenta?

Answer 21

diffusion, high maternal low vs fetal

Question 22

How is glucose transported across placenta?

Answer 22

transporters on maternal side and fetal trophoblast cells

Question 23

How is water transported across placenta?

Answer 23

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

Question 24

How is electrolytes transported across placenta?

Answer 24

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

Question 25

How is amino acids transported across placenta?

Answer 25

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

Question 26

What maternal changes occur to allow maternal fetal oxygen exchange?

Answer 26

CO increase by 30% during first trimester

peripheral resistance decrease up to 30%

maternal blood volume increases to 40%

pulmonary ventilation increases 40%

Question 27

What placenta and fetal changes occur to allow maternal fetal oxygen exchange?

Answer 27

• Placenta consumes 40-60% glucose and O2 supplied
• But although fetal O2 tension is low, O2 content and saturation are similar to maternal blood.
• Embryonic and fetal hemoglobins: greater affinity for O2 than maternal hemoglobin.