placenta/pregnancy 1 Flashcards
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
