Lecture 34: Placenta and Fetal Membranes

Question 1

What are the fetal membranes?

Answer 1

Chorion, amnion, umbilical vesicle and allantois

Question 2

What is the major function of the placenta?

Answer 2

-exchange nutrients and O2 between maternal and fetal bloodstreams

Question 3

After formation of the blastocyst, what happens to the embryo?

Answer 3

Divides into embryoblast and trophoblast and implants on the endometrium

Embyroblast - froms the bilaminar disc
Trophoblast - differentiates into syncytiotrophoblast and cytotrophoblast

Question 4

What is the decidua and what are the layers?

Answer 4

forms on the endometrium and directs embryo implantation

Decidua basalis - innermost (fetus “lies” on it)
Decidua capsularis - envelopes most of the chorion
Decidua parietalis - wraps around the mucous plug

Question 5

How does implantation establish the primordial placenta?

Answer 5

syncytiotrophoblast invades the decidua > lacunae appear in the syncytiotrophoblast layer > lacunae will fuse to form the lacunar network > maternal blood flows into the network = uteroplacental circulation

Question 6

What is ectopic pregnancy and what are its symptoms?

Answer 6

• embryo implants somewhere else other than uterine fundus (usually oviduct)
• AP, vag bleed, amenorrhea, slower HCG production, oviduct rupture

Question 7

What is the chorionic sac and what are its components?

Answer 7

• the sac that encloses the embryo (wraps around the amnion)

- altogether made of the extraembryonic somatic, splanchnic mesoderms and coelom

Question 8

What is the amniotic sac?

What is its fate?

Answer 8

• forms inside the chorion from amnioblasts separating from epiblasts, contains the fetus and the amniotic fluid
• as fetus grows, the amnion enlarges and fills up the chorionic cavity and form the amniochorionic membrane

Question 9

Which fetal systems is the amniotic fluid derived from?

Answer 9

-urinary (mostly), respiratory and GI tracts, more made as pregnancy grows

Question 10

Hydroamnios vs. Oligohydramnios

Clinical

Answer 10

Hydroamnios:
Excess amniotic fluid, AP, bloating, swelling breathlessness

Oligohydramnios:
Not enough amniotic fluid, can lead to renal/pulmonary hypoplasia/developmental abnormalities

Question 11

What is the fate of the decidua capsularis?

Answer 11

degenerates at 22-24 weeks causing the smooth chorion to fill the uterine cavity

Question 12

What are the two components of the placenta?

Answer 12

Fetal part - chorionic villi that extend into the intervillous space
Maternal part - decidua basalis (derived from the decidua)

Question 13

How does the chorion attach to the decidua basalis?

Answer 13

cytotrophoblasts proliferate from the chorionic plate and invade the decidua basalis (and into the syncytiotrophoblast layer)

Question 14

Why does the placenta only forms at one part of the chorion?

Answer 14

initially (wk 2) the chorionic villi will grow around the entire chorion > (wk 8) only the villi connected to the decidua basalis remains (villious chorion), the rest will obliterate (smooth chorion)

Question 15

After the final villious chorion is formed, what happens?

Answer 15

Villious chorion continues to invade decidua basalis > branches around the lacunae and forms the intervillous space and placental septa > blood flows into the intervillous space at wk 11 -14

Part of the decidua basalis that is furthest in becomes the cytotrophoblastic shell

Question 16

What is the difference between main stem villi, branch villi and anchoring villi

Answer 16

Main stem: extends from the chorionic plate
Branch: branches from the main villi
Anchoring villi: grows from the cytotrophoblastic shell

Question 17

Primary villi vs. Secondary villi vs Tertiary villi

Answer 17

Primary: cytotrophoblast core grows as villi (syncytiotrophoblast covers it)

Secondary: Extrembryonic mesoderm core/connective tissue forms

Tertiary: capillaries start to form in the core as well

Question 18

What types of things are transported via the placenta?

What types of things CANNOT cross the placenta?

Answer 18

Nutrients, hormones, IgG, waste products, drugs, viruses

protein hormones, bacteria, AA like drugs

Question 19

How does the umbilical cord develop?

Answer 19

connecting stalk enlarges with the fetus and forms the cord > develops 2 umbilical arteries and 1 umbilical vein

*arteries carry deoxygentated to placenta, vein carries oxygenated to fetus)

Question 20

Placenta previa vs acreta

complications/symptoms

Answer 20

Previa: plaenta implants on lower uterine segment = leads to 3rd trimester bleeding

Acreta: partial or complete absence of the decidua causing the villious chorion to attach to the myometrium instead = can cause post partum bleeding since fetus is attached to muscular layer of uterus

Question 21

Partial vs. Complete Hydatidiform mole

Answer 21

Partial: portion of villi replaced by dilated vesicles, caused by normal ovum polyspermy

Complete: all villi replaced by dilated vesicles, caused fertilization of empty ovum or polyspermy

Question 22

Invasive Mole

Answer 22

• complete mole penetrates the uterine wall

- high hCG, aggressive invasion of wall can cause hemorrhaging

Question 23

Gestational choriocarcinoma

Answer 23

• metastatic tumor coming from trophoblasts, usually associated with molar pregnancies
• high hCG w/o uterine enlargement

Question 24

Monozygotic vs Dizygotic twins

Answer 24

Monozygotic: originate from 1 zygote (placenta is shared)

Dizygotic: originate from 2 zygote (each zygote develops its own placenta)