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Flashcards in placenta/pregnancy 2 Deck (27):

why are spiral arteries crucial for the success of pregnancy

spiral arteries carry the maternal blood which perfuses the placenta and placenta extracts oxygen and nutrients for the fetus

-haemochorial nutrition


what does the embryo eat while the spiral arteries are plugged

uterine gland contains glandular 'milk'
- this is secreted into the intervillous space
- consumed as a major energy source in the first few weeks of pregnancy after initial implantation

= histiotrophic nutrition


define villous

branch of the placenta


define villous cytotrophoblast

trophoblast progenitor cell type found mainly in the 1st trimester underlying the syncytiotrophoblast


define syncytiotrophoblast

surface layer of the placenta formed by fusion of villicytotrophoblast
syncytotrophoblast doesnt replicate but is replaced by fusion of additional villicytotrophoblast


extravillous cytotrophoblast

differentiated cells that have migrated out of the villous placenta towards the maternal tissues


structural changes in the placenta with gestational age

1. during early pregnancy stroma of the villi become more cellular and more vascularised
2. during 2nd trimester villous cytotrophoblast thins down
3. during 3rd trimester viloous cytotrophoblast is spare
4. branching of villi increases
5. size of placenta increases


diameter of pacenta throughout

12 weeks = 56mm

38 weeks = 220mm and 0.5kg


types of decidua

decidua basalis - decidua underlying the implantation site

decidua capsularis - decidua overlying the implantation site

decidua peritalis - decidua around the remainder of the uterus


maternal contributions to the placenta

as gestation progresses the amniotic cavity enlarges obliterating the uterine cavity

the decidua capsularis then fuses with the decidua peritalis


placental membranes

amnion - avascular covers cord and placenta (closes to baby)

chorion - fetal vessels (sits next to amnion)


umbilical cord

formed from the yolk sac and allantois

vessels of the cord are derived from the allontois

- 2 arteries
- 1 vein (carries oxygenated blood)

- between the 3 vessels is whartons jelly
-consists of a network of myofibroblasts and spaces are filled with mucopolysaccharides (*keeps cord turgid)


importance of whartons jelly

keeps cord turgid and prevents compression of vessels in umbilical cord


placenta adaptations to increase transport

1. villous structure is tortuous with a large surface area

2. syncytiotrophoblast has a microvillous surface (slows down movement of maternal blood across placenta)

3. in 3rd trimester most villi are small tertiary villi

4. in the 3rd trimester the fetal capillaries are closely apposed to the syncytiotrophoblast


fetal Hb

adapted to 'suck' oxygen from maternal blood

fetal Hb has a greater affinity for oxygen

at a standard pO2
- fetal = 80% saturated
- adult = 50% saturated

fetal blood has more Hb and can carry more oxygen than maternal


the Bohr effect

as maternal blood picks up fetal metabolites the pH lowers
-thus, the affinity for O2 decreases and dissociation of O2 increases

the converse occurs of the fetal side
-double Bohr effect


the haldane effect

capacity of Hb to bind CO2 is related to the amount of bound O2
-thus, if O2 is lost from maternal blood capacity of maternal blood for CO2 increases

the converse occurs of the fetal side
-double Haldane effect


function of amniotic fluid

1. bouyant medium allows symmetric growth
2. cushions the embryo/fetus
3. prevents adhesions of the fetus with the membranes
4. allows the fetus to move - muscle development
5. development of GI/respiratory tracts - breathing and swallowing (practise movements)


origins of amniotic fluid

1. initially ultrafiltrate of maternal plasma
2. major fetal contribution
3. 20+ weeks fetal urine and surface of placenta and cord


volumes of amniotic fluid over time

10 weeks = 30mls

35 weeks = 1L

human fetal urine output estimated at approx 500-1200mls/day


amniotic fluid recycling

fluid leaves the amniotic cavity mainly by fetal swallowing

fluid can also move across the fetal skin (prior to keratinisation at 24 weeks)

fluid can move across the fetal membranes into the maternal circulation or into the fetal vessels of the placenta and umbilical cord



excessive amniotic fluid possibly due to loss of swallowing

found in many cases of diabetic pregnancy



lack of amniotic fluid potentially due to kidney problems


clinical importance of amniotic fluid


chorionic villi sampling

used to screen for anomalies


what does the placenta usually prevent transmission of

Malaria - can cause clogging of placenta


what is the placenta not a barrier against

small pox and other related viruses
Toxoplasmosis - from cats and raw meats


drugs in pregnancy

ethanol - crosses the placenta may cause FAS

recreational drugs - may cause IUGR and development delays

paracetamol & aspirin - crosses placenta but it safe

heparin - doesnt cross placenta

warfarin - crosses placenta causes fetal malformations