Placentation Flashcards
How is early embryo nutrition given?
Histiotrophic:
reliant on uterine gland secretions and breakdown of endometrial tissues
Why is embryo fetal growth during the first trimester limited?
Due to the histiotrophic nature of nutrition
At the start of the 2nd trimester what nutrition is used?
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
What does the amnion do? (inner fetal membrane)
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
What is the connecting stalk?
Links developing embryo unit to the chorion
What are trophoblastic lucaenea?
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
What are fetal membranes?
extraembryonic tissues that form a tough but flexible sac encapsulates the fetus and forms the basis of the maternal-fetal interface.
What is the chorion? (outer fetal membrane)
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
What is the allantois?
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
How is the amniotic sac made with both fetal membranes involved?
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
What are primary chorionic villi?
cytotrophoblast finger like projection through the syncitiotrophoblast layer into maternal endometrium
What is the purpose of the chorionic villi?
substantial SA for exchange of gases and nutrtients
these projections undergo branching
What are the three phases of chorionic villi development?
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
How do the villi change from early pregnancy to late pregnancy?
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.
What does the convulation and dilated of the villi allow?
Slow blood flow in vessels for better exchange
Describe the maternal blood supply to the endometrium?
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
WHat do extra villus trophoblast cells do? (EVT cells)
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
What does conversion mean?
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
What nutrients are being exchanged across the placenta?
O2 Glucose Water Electrolytes Calcium Amino acids
How is calcium transported across placenta?
active transport by Mg ATPase calcium pump
How is Oxygen transported across placenta?
diffusion, high maternal low vs fetal
How is glucose transported across placenta?
transporters on maternal side and fetal trophoblast cells
How is water transported across placenta?
placenta main site of exchange, though some crosses amnion-chorion. Majority by diffusion, though some local hydrostatic gradients.
How is electrolytes transported across placenta?
large traffic of sodium and other electrolytes across the placenta – combination of diffusion and active energy-dependent co-transport.
How is amino acids transported across placenta?
reduced maternal urea excretion and active transport of amino acids to fetus
What maternal changes occur to allow maternal fetal oxygen exchange?
CO increase by 30% during first trimester
peripheral resistance decrease up to 30%
maternal blood volume increases to 40%
pulmonary ventilation increases 40%
What placenta and fetal changes occur to allow maternal fetal oxygen exchange?
- 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.
