Foetal Growth and Placentation Flashcards
Describe early embryo nutrition with a word.
histiotrophic
Early embryo is reliant on what for nutrition?
uterine gland secretions and breakdown of endometrial tissues
At the start of the 2nd trimester, embryo switches from histiotrophic to ______ support.
haemotrophic
How is haemotrophic support achieved in humans?
through a haemochorial-type placenta where maternal blood directly contacts the fetal membranes
Define chorion.
outermost membrane surrounding an embryo
What is the connecting stalk?
links embryo to chorion
What are trophoblastic lacunae
Large spaces filled with maternal blood formed by breakdown of maternal capillaries and uterine glands
Become intervillous spaces aka maternal blood spaces
Define amnion.
innermost membrane that encloses the embryo
Define foetal membranes.
extraembryonic tissues that form a tough but flexible sac encapsulates the fetus and forms the basis of the maternal-fetal interface
The amnion arises from?
epiblast
The amnion goes on to form?
closed, avascular sac with developing embryo at one end
Amniotic sac is filled with?
amniotic fluid
Amniotic fluid is secreted from what week?
5th week
Functions of amniotic sac
encapsulates and protects the embryo
The chorion arises from?
yolk sac derivatives and the trophoblast
Is the chorion avascular or highly vascularised?
highly vascularised
The chorion gives rise to?
chorionic villi
What are chorionic villi?
outgrowths of cytotrophoblast from the chorion that form the basis of the fetal side of the placenta
Amniotic sac is formed of what two layers?
amnion on the inside
chorion on the outside
What is the allantois?
outgrowth of the yolk sac
Allantois grows along?
connecting stalk from embryo to chorion
Allantois goes on to?
becomes coated in mesoderm
vascularises to form umbilical cord
Primary chorionic villi
Cytotrophoblast forms finger-like projections through syncitiotrophoblast layer Into maternal endometrium
Function of chorionic villi
provide substantial surface area for exchange
List the three phases of chorionic villi development.
primary
secondary
tertiary
primary phase of chorionic development
outgrowth of the cytotrophoblast and branching of these extensions
secondary phase of chorionic development
growth of the fetal mesoderm into the primary villi
tertiary phase of chorionic development
growth of the umbilical artery and umbilical vein into the villus mesoderm, providing vasculature.
Maternal blood supply to the endometrium
Uterine artery branches > network of arcuate arteries > radial arteries >
basal arteries form spiral arteries during menstrual cycle endometrial thickening
Spiral artery remodelling
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
How does the foetus get oxygen?
across placenta via diffusion (high maternal O2 tension, low fetal O2 tension)
How does the foetus get glucose?
facilitated diffusion by transporters on maternal side and fetal trophoblast cells
How does the foetus get water?
placenta main site of exchange, though some crosses amnion-chorion. Majority by diffusion, though some local hydrostatic gradients
How does the foetus get electrolytes?
large traffic of sodium and other electrolytes across the placenta – combination of diffusion and active energy-dependent co-transport
How does the foetus get calcium?
actively transported against a concentration gradient by magnesium ATPase calcium pump.
How does the foetus get amino acids?
reduced maternal urea excretion and active transport of amino acids to foetus
Maternal changes for maternal-foetal oxygen exchange
^CO 30% in 1st trimester, peripheral resistance decreases 30%, ^blood vol by 40%, ^ pulmonary ventilation 40%
Compare O2 content and saturation of foetal and maternal blood.
similar
Which has a greater affinity for O2: maternal haemoglobin or foetal haemoglobin?
foetal haemoglobin
