Lecture 34: Placenta and Fetal Membranes Flashcards
What are the fetal membranes?
Chorion, amnion, umbilical vesicle and allantois
What is the major function of the placenta?
-exchange nutrients and O2 between maternal and fetal bloodstreams
After formation of the blastocyst, what happens to the embryo?
Divides into embryoblast and trophoblast and implants on the endometrium
Embyroblast - froms the bilaminar disc
Trophoblast - differentiates into syncytiotrophoblast and cytotrophoblast
What is the decidua and what are the layers?
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
How does implantation establish the primordial placenta?
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
What is ectopic pregnancy and what are its symptoms?
- embryo implants somewhere else other than uterine fundus (usually oviduct)
- AP, vag bleed, amenorrhea, slower HCG production, oviduct rupture
What is the chorionic sac and what are its components?
- the sac that encloses the embryo (wraps around the amnion)
- altogether made of the extraembryonic somatic, splanchnic mesoderms and coelom
What is the amniotic sac?
What is its fate?
- 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
Which fetal systems is the amniotic fluid derived from?
-urinary (mostly), respiratory and GI tracts, more made as pregnancy grows
Hydroamnios vs. Oligohydramnios
Clinical
Hydroamnios:
Excess amniotic fluid, AP, bloating, swelling breathlessness
Oligohydramnios:
Not enough amniotic fluid, can lead to renal/pulmonary hypoplasia/developmental abnormalities
What is the fate of the decidua capsularis?
degenerates at 22-24 weeks causing the smooth chorion to fill the uterine cavity
What are the two components of the placenta?
Fetal part - chorionic villi that extend into the intervillous space
Maternal part - decidua basalis (derived from the decidua)
How does the chorion attach to the decidua basalis?
cytotrophoblasts proliferate from the chorionic plate and invade the decidua basalis (and into the syncytiotrophoblast layer)
Why does the placenta only forms at one part of the chorion?
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)
After the final villious chorion is formed, what happens?
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
What is the difference between main stem villi, branch villi and anchoring villi
Main stem: extends from the chorionic plate
Branch: branches from the main villi
Anchoring villi: grows from the cytotrophoblastic shell
Primary villi vs. Secondary villi vs Tertiary villi
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
What types of things are transported via the placenta?
What types of things CANNOT cross the placenta?
Nutrients, hormones, IgG, waste products, drugs, viruses
protein hormones, bacteria, AA like drugs
How does the umbilical cord develop?
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)
Placenta previa vs acreta
complications/symptoms
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
Partial vs. Complete Hydatidiform mole
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
Invasive Mole
- complete mole penetrates the uterine wall
- high hCG, aggressive invasion of wall can cause hemorrhaging
Gestational choriocarcinoma
- metastatic tumor coming from trophoblasts, usually associated with molar pregnancies
- high hCG w/o uterine enlargement
Monozygotic vs Dizygotic twins
Monozygotic: originate from 1 zygote (placenta is shared)
Dizygotic: originate from 2 zygote (each zygote develops its own placenta)
