Lecture 11: Placenta/pregnancy

Question 1

Other relevance of pre-eclampsia for all you GPs out there? (@saikonan)

Answer 1

There is a massively increased risk of early CVD mortality in women who have had pre-eclampsia during one of their pregnancies.

Question 2

Essential functions of the placenta?

Answer 2

• Self-maintenance/renewal
• exchange/transport/transfer (blood does NOT mix)
• seperation from mother
• protection from maternal infections
• protection from the maternal immmune system

Question 3

Nidation? specifics?

Answer 3

At the leading edge there is enzymes excreted by the embryo, it always heads in with the inner cell mass going in first. This process takes 4-5 days before the embryo is completely inside the wall of the uterus.

The real placenta exista from day 12

Question 4

The make up of the real placenta?

Answer 4

• From about day 12 the villous period begins
• Cytotrophoblasts proliferate and invade the trabeculae - these become primary villi
• The lacunar system is now called the intervillous space
• At day 14 cells of the extraembryonic mesenchyme invade the primary villi forming secondary villi
• At about day 18-20 PC capillaries form in the villi - tertiary villi
• from here on almost all villi are tertiary with their vessels connecting to the umbilical vessels carrying blood to and from the fetus

Question 5

How and where does exchange occur?

Answer 5

Floating villi

Most villi do not have contact with the maternal tissues but are suspended in the intervillous space where maternal blood flows freely, here exchange occurs. This is also the site of barrier functions of the placenta.

Question 6

Position of villi and their names?

Answer 6

Villi initially surround the implanted embryo

Those on the sides and towards the uterine lumen regress to form the smooth chorion - Chorion laeve

Those villi at the bas of the implantation site form the definitive placenta - Chorion frondosum

Question 7

Features of anchoring villi?

Answer 7

Seen more in first trimester, physically anchor the placenta to the uterine wall. Cytotrophoblasts break through the syncytiotrophoblast and invade deeply into the uterus.

The villous cytotrophoblasts replace the epithelial cells and SMC around the spiral arteries as far as 1/3 of the way into the myometrium (never veins)- means they no longer respond to tonic signals from the mother. (eg. in fright or flight blood supply is still in the maintained to the fetus)

Question 8

Is it algood to be a skinny nigga in the womb?

Answer 8

Nah, 10x high chance of still births in small for gestational age babies. (4.3% instead of 0.4%)

Question 9

Protection of the early developing placenta?

Answer 9

Endovascular trophoblast plugs form a sieve like structure to protect from arterial pressure. This does however mean that only plasma can go through. (for the first 8-12 weeks)