placenta/pregnancy 1

Question 1

preeclampsia and stats

Answer 1

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

Question 2

essential functions of the placenta

Answer 2

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

Question 3

placenta and the blood supplies

Answer 3

Maternal and fetal blood circulations are completely separate

they do not mix

the placenta brings them into close apposition

Question 4

define nidation

Answer 4

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)

Question 5

what happens shortly after nidation

Answer 5

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.

Question 6

define origin of trophoblast

Answer 6

when implantation occurs trophectoderm cells become trophoblasts

Question 7

when does the ‘real placenta’ exists

Answer 7

from day 12

the villous period begins

Question 8

what percentage of conceptions are lost

Answer 8

70% of conceptions are lost

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

Question 9

what changes happen to the placenta during day 12

Answer 9

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

Question 10

the placenta at about day 18-20

Answer 10

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

Question 11

floating villi

Answer 11

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

Question 12

chorion laeve

Answer 12

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

Question 13

chorion frondosum

Answer 13

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

Question 14

7.5 week placenta

Answer 14

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

Question 15

anchoring villi

Answer 15

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

Question 16

what physiological changes occur in the arteries at mid-gestation

Answer 16

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

Question 17

consequences of small for gestational age babies (SGA)

Answer 17

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

Question 18

plugged spiral arteries

Answer 18

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

Question 19

consequences of plugging spiral arteries

Answer 19

(red cells cant pass through but plasma can)

Therefore early gestation placenta develops in very low oxygen

Question 20

what eventually happens to spiral plugs

Answer 20

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