Late fetal development Flashcards
What is early embryo nutrition reliant on?
Where does it switch its nutrient source to at the start of second semester ?
it is Histotrophic
reliant on uterine secretions and breakdown of uterine lining
haemotrophic
achieved via a haemochorial- type placenta
where maternal blood supply directly contacts fetal membranes
What is the inner Fetal membrane?
what does it arise from?
what does it form?
what does it do?
the Amnion
epiblast
a closed avascular sac with the developing embryo at one end
fluid filled sac encapsulates the embryo to protect it
begins to secrete amniotic fluid by the 5th week
what is the outer fetal membrane
what is it formed from
what does it give rise to
the chorion
yolk sac derivatives and trophoblasts
chorionic villi- outgrowths of the cytotrophoblast from the chorion that form the basis of the fetal side of the placenta
what is the allantois
where does it grow to and from
what does it become
outgrowth of the yolk sac
down the connecting stalk from embryo to chorion
coated in mesoderm and vascularised to form umbilical cord
what are the foetal membranes
how is the amniotic sac formed
what are the two layers of the amniotic sac
Extraembryonic tissues that encapsulate the foetus by forming a tough but flexible sac, forms the basis of the maternal-foetal interface
amnion cells secrete fluid , causing fluid to accumulate and amnion cells to come into contact with the chorion, forms the amniotic sac
amnion cells on the inside, chorion cells on the outside
what is the chronic villi and what do they do?
what are the three stages of villi development?
finger like extensions of the chorionic cytotrophoblast, which undergo branching
provides a larger surface area for exchange
primary- when finger like cytotrophoblast projections form through the syncitiotrophoblast layer to the maternal endometrium layer. begin to branch
secondary- fetal mesoderm grows into villi
tertiary- vasculature is provided by the umbilical artery and vein growing into the villus mesoderm
why are the ends of the villi convoluted knots and more dilated vessels?
what is the difference in the villi between early and late pregnancy
slows down blood flow so more time for exchange between maternal and fetal blood
Early pregnancy: 150-200µm diameter, approx. 10µm trophoblast thickness between capillaries and maternal blood.
Late pregnancy: villi thin to 40µm, vessels move within villi to leave only 1-2µm trophoblast separation from maternal blood.
what is the order of arteries formed from maternal blood to fetal?
Uterine artery branches give rise to a network of arcuate arteries.
Radial arteries branch from arcuate arteries, and branch further to form basal arteries.
Basal arteries form spiral arteries during menstrual cycle endometrial thickening.
why are spiral arteries converted?
How are spiral arteries converted?
Conversion: turns the spiral artery into a low pressure, high capacity, to ensure continuous and extensive blood flow.
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 are various nutrients transported across the placenta ?
Oxygen: diffusional gradient (high maternal O2 tension , low fetal O2 tension)
Glucose: facilitated diffusion by transporters on maternal side and foetal trophoblast cells.
Water: placenta main site of exchange, though some crosses amnion-chorion. Majority by diffusion, though some local hydrostatic gradients.
Electrolytes: large traffic of sodium and other electrolytes across the placenta – combination of diffusion and active energy-dependent co-transport.
Calcium: actively transported against a concentration gradient by magnesium ATPase calcium pump.
Amino acids: reduced maternal urea excretion and active transport of amino acids to fetus
how do the mothers…change ?
- cardiac output
- peripheral resistance
- blood volume
- pulmonary ventilation
Maternal cardiac output increases 30% during first trimester (stroke vol & rate)
Maternal peripheral resistance decreases up to 30%
Maternal blood volume increases to 40% (near term (20-30% erythrocytes, 30-60% plasma)
Pulmonary ventilation increases 40%
How much glucose and 02 does the placenta consume?
how is the 02 conc and glucose conc related to the maternal?
Which haemoglobin has a higher affinity- fetal or maternal?
Placenta consumes 40-60% glucose and O2 supplied
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.
How does the circulatory system work in a developing fetus
Hints:
- placenta?
- vascular shunts?
- ventricles?
Placenta acts as site of gas exchange for fetus
Ventricles act in parallel rather than series
vascular shunts bypass pulmonary & hepatic circulation -> close at birth
How does the respiratory system work in a developing fetus?
Hints:
when do primitive air sacs form?
when does vascularisation occur?
when does surfactant production occur?
Primitive air sacs form in lungs around 20 weeks, vascularization from 28 weeks
Surfactant production begins around week 20, upregulated towards term
Foetus spends 1-4h/day making rapid respiratory movements during REM sleep
What is labour?
Safe expulsion of the fetus at the correct time
Expulsion of the placenta and fetal membranes
Resolution/healing to permit future reproductive events
