Lecture 11: The Placenta and pregnancy (I)

Question 1

What are the essential functions of the placenta

Answer 1

1) self maintainence/renewal
2) exchange/transport/transfer
3) separation
4) protection from maternal infections
5) protection from the maternal immune system

Question 2

What is the placenta?

Answer 2

The placenta is an organ that develops in your uterus during pregnancy.

This structure provides oxygen and nutrients to your growing baby and removes waste products from your baby’s blood. The placenta attaches to the wall of your uterus, and your baby’s umbilical cord arises from it.

Question 3

The maternal and fetal blood circulations are……

They do or do not mix

The placenta brings them into close apposition

Answer 3

Completely separate

They do NOT mix

The placenta brings them into close apposition

(pic = from the side of the mother/maternal side)

Question 4

What is Nidation?

Answer 4

The point in time the embryo attaches to the epithelial cells of the uterine lining.

Question 5

Describe the process of nidation in the first 12 days? (not very important)

Answer 5

Nidation: The point in time the embryo attaches to the epithelial cells of the uterine lining.

A) Adhesion:

-Human embryos always implanted with the inner cell mass at the leading edge. At the leading edge, the trophectoderm (becomes trophoblast) attaches and starts to secrete enzymes (proteases etc. ) and start to eat away at the uterine wall

B) 8 days

C) 12 days

• Embryo has buried itself entirely into the wall of the lumen (not in the lumen)
• Uterine wall heals

D) End of lacunar phase

Question 6

What is the human placenta made up of?

Answer 6

Chorionic villi

Chorionic villi are villi that sprout from the chorion to provide maximum contact area with maternal blood.

Question 7

The ‘real placenta’ exists from day 12 so why do I care about the placenta and its first days?

Answer 7

Preclampsia presents after 20 weeks of gestation but we believe that it is established long before then.

Question 8

What is preeclampsia?

Answer 8

Preeclampsia is a condition that pregnant women develop.

It is marked by _high blood pressur_e in women who have previously not experienced high blood pressure before. Preeclamptic women will have a high level of protein in their urine and often also have swelling in the feet, legs, and hands.

This condition usually appears late in pregnancy although it can occur earlier.

If undiagnosed, preeclampsia can lead to eclampsia, a serious condition that can put you and your baby at risk, and in rare cases, cause death. Women with preeclampsia who have seizuresare considered to have eclampsia.

Question 9

From day 12 the ____ period begins and the placenta is considered the _________

Answer 9

From about day 12, the villous period begins and the placenta is now considred the r_eal placenta_

Question 10

Describe the formation of the different types of Villi (4 types)

Answer 10

Becomes the “real” placenta

• Cytotrophoblasts (inner layer of the trophoblast.) proliferate and invade the trabeculae- these become primary villi
• The lucanar system (gaps between them) is now called the intervillous space
• At about day 14, cells in the extraembryonic mesenchyme invade the primary villi forming secondary villi
• About 18-20 days pcc capillaries form the villi, tertiary villi
• From this point on, almost all villi are tertiary
• The vessels in the villi conects to the umbilical vessels carrying b_lood to and from the fetus_.
• Floating Villi:
  
  • Most villi do not have contact with the maternal tissues but are suspended in the intervillous space. These are called floating villi.
  • Floating villi are responsible for the exchange and barrier functions of the placenta

Question 11

Placenta is initially ______ (shape)

Answer 11

Spherical (not flat)

Question 12

Villi initially surround ________

The villi towards the uterine lumen regress to form ______

The villi are the base of the implanation from ________

Answer 12

Villi initially surround the implanted embryo

• Those villi to the sides and towards the uterine lumen regress to form
the smooth chorion Chorion Laeve

• Those villi at the base of the implantation site form the definitive
placenta Chorion Frondosum

Question 13

• Those villi to the sides and towards the uterine lumen regress to form
the ____________

Answer 13

• Those villi to the sides and towards the uterine lumen regress to form
the smooth chorion Chorion Laeve

Question 14

• Those villi at the base of the implantation site form the definitive
_________

Answer 14

• Those villi at the base of the implantation site form the definitive
placenta Chorion Frondosum

Question 15

Describe the changes in the Villi at 7.5 weeks in the placenta

Answer 15

Villi regresses.

• The placenta forms essentially as a sphere surrounding the embryo but as gestation progresses
• villi to the sides and luminal aspect regress to form the smooth chorion
• Only villi basal to the implantation site remain as the definitive placenta

Question 16

At 7.5 weeks,

villi in the _________ regress to form the smooth chorion

only villi _______ to the implantation site remain as the definitive placenta

Answer 16

villi to the sides and luminal aspect regress to form the smooth chorion (membrane)

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

Question 17

What are the 2 types of villi in the placenta?

Answer 17

1) Floating villi (make up almost 100% of villi in the placenta)
2) Anchoring villi
- See them more in the 1st trimester
- Anchor the placenta to the uterine wall

Question 18

Describe the Anchoring Villi

Answer 18

• See them more in the 1st trimester
• Anchor the placenta to the uterine wall
• In a few villi cytotrophoblasts(The cytotrophoblast (or layer of Langhans) is the inner layer of the trophoblast) break through the syncytiotrophoblast (epithelial covering of the highly vascular embryonic placental villi, which invades the wall of the uterus to establish nutrient circulation between the embryo and the mother.)
• The cytotrophoblast spread laterally around the implantation site forming a cytotrophoblastshell
• The trophoblast shell remains in contact with the maternal tissue throughout gestation
• Columns of cytotrophoblast continue to stream out of these anchoring villi to invade the decidua (The decidua is the uterine lining (endometrium) during a pregnancy,) and spiral arteries during the first and second trimesters.

Question 19

What is the decidua?

Answer 19

The decidua is the uterine lining (endometrium) during a pregnancy,

Question 20

What are cytotrophoblasts?

Answer 20

is the inner layer of the trophoblast

Question 21

What is the syncytiotrophoblast

Answer 21

(epithelial covering of the highly vascular embryonic placental villi, which invades the wall of the uterus to establish nutrient circulation between the embryo and the mother.)

Question 22

What is a blastocyst?

Answer 22

Blastocyst, a distinctive stage of a mammalian embryo

Question 23

What happens to the spiral arteries mid gestation?

Answer 23

(if the mother is surprised, fight and flight response will kick in, which will restrict the blood supply to the fetus which can be detrimental)

The fetus sends villous cyototrophoblasts down into the spiral arteries,

They disgest the endothelial and smooth muscle cells

So when the mother is suprised, the spiral arteries are not able to constrict.

Question 24

Give 2 examples of indaequate “physiological changes” during pregnancy

Answer 24

1) Inadequate depth of trophoblast invasion (Trophoblasts are not transformed to the full depth)
2) Reduced number of vessels transformed

The fetus is grwoth restricted.

Question 25

What are some consequences of being SGA (small gestational age) (growth restricted)

Answer 25

SGA babies are more likely to be born prematruely and be stillborn

Question 26

Shortly after implantation (before the spiral arteries widen - so they can’t constrict) they……

Why is this important?

Answer 26

Become blocked off

(plugged spiral arteries)

Thought to r_educe the arterial pressure_ and p_rotect the developing placenta._

They’re more like sieves than plugs. RBC cannot pass here. So in the first 8-10 weeks of gestation, the placenta is not perfused by maternal blood. It is perfused by maternal plasma. The consequence of this is the early gestation placenta is n_ot well perfused_.