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Flashcards in placenta/pregnancy 1 Deck (20):

preeclampsia and stats

hypertension specific to second half of human pregnancy

occurs 20 weeks after gestation

3-8% of all pregnancies

~60,000 maternal deaths/year

3,000 NZ women annually


essential functions of the placenta

- self-maintenance/ renewal
- exchange/transport/transfer
- separation
- protection from maternal infections
- protection from the maternal immune system


placenta and the blood supplies

Maternal and fetal blood circulations are completely separate

they do not mix

the placenta brings them into close apposition


define nidation

the point in time when an embryo attaches to the epithelial cells of the uterine lining
- always implant with the inner cell mass at the leading edge (primitive syncytium)


what happens shortly after nidation

trophectoderm secretes enzymes e.g. proteases and they start to eat away uterine wall. It digest a hole for the embryo to move into until the embryo it entirely buried in the wall uterus.


define origin of trophoblast

when implantation occurs trophectoderm cells become trophoblasts


when does the 'real placenta' exists

from day 12

the villous period begins


what percentage of conceptions are lost

70% of conceptions are lost

only 30% are live births e.g. humans are infertile


what changes happen to the placenta during day 12

cytotrophoblasts proliferate and invade the trabeculae - these become primary villi

the lucanar system is now called intervillous space

~day 14 cells of the extraembryonic mesenchyme invade the primary villi forming secondary villi

trophectoderm cells that surround the inner cell mass become trophoblasts


the placenta at about day 18-20

capillaries form in the villi tertiary villi

from this point on almost all villi are tertiary

the vessels in the villi connect to the umbilical vessels carrying blood to and from the fetus


floating villi

name given to most villi that dont have contact with the maternal tissues but are suspended in the intervillous space

they're responsible for the exchange and barrier functions of the placenta


chorion laeve

name given to the villi on the sides and back of the embryo


chorion frondosum

the villi at the leading edge that become the disc of placenta at term


7.5 week placenta

villi begin to regress

sides and luminal aspect regress to form the smooth chorion (forms fetal membrane later)

only villi basal to implantation site remain as the definitive placenta/disc


anchoring villi

anchor placenta to the uterine wall

syncytiotrophoblast covers the whole surface of the placenta and every so often you get little breaks in it. Causing cytotrophoblasts to break through, proliferate, migrate through the syncytiotrophoblast into the maternal tissue and invade deeply into the uterus

columns of cytotrophoblasts continue to stream out of these anchoring villi to invade the decidua and spiral arteries during the 1st and 2nd trimesters


what physiological changes occur in the arteries at mid-gestation

extra-villous trophoblast invades out of the placenta and into the spiral arteries, replacing the endothelial cells lining the spiral arteries. (loss of muscular wall) become endovascular trophoblasts
-never invade the veins
-loss of tonic signals from mother
-invasion needs to be deep


consequences of small for gestational age babies (SGA)

occurs from extra-villous trophoblast not fully invading the spiral arteries, leads to growth restriction

babies more likely to be born prematurely and be stillborn


plugged spiral arteries

endovascular trophoblast plugs are formed at the end of spiral arteries in the lumen to prevent damage to the placenta
-reduce arterial pressure and protect developing placenta


consequences of plugging spiral arteries

(red cells cant pass through but plasma can)

Therefore early gestation placenta develops in very low oxygen


what eventually happens to spiral plugs

they gradually disperse and allow maternal arterial blood to perfuse the intervillous space. exchange between fetal blood and maternal circulation takes place