Placental and Fetal Membranes Flashcards
What is a fetomaternal organ?
placenta
What is the fetal part of the placenta?
chorionic sac (outermost fetal membrane) -->more specifically, villous chorion that projects into intervillous space where maternal blood is
What is the maternal part of the placenta?
Decidua basalis
–>endometrium deep to fetus
What are examples of fetal membranes?
chorion
amnion
umbilical vesicle
allanosis
What are the extraembryonic structures that develop from trophoblast of blastocyst?
amnion
umbilical vesicle
connecting stalk
chorionic sac
When does the blastocyst become a bilaminar embryonic disc?
when implantation occurs
–>10 days post-fertilization
What are the 2 cell lineages in the blastocyst?
blastocyst is TOTIPOTENT
–>embryoblast (embryo)
–>trophoblast (extraembryonic tissue)
What is the fxnl layer of endometrium that separates from the remainder of the uterus after childbirth?
decidua
What part of the endometrium is deep to the fetus and forms the maternal part of the placenta?
decidua basalis
What part of the endometrium is superficial and overlies the fetus?
decidua capsularis
What part of the endometrium makes up the remaining decidua?
decidua parietalis
–>between capsularis and basalis
What is the decidual reaction?
cellular and vascular changes as the blastocyst implants
What does the trophoblast differentiate into as the blastocyst implants?
-Cytotrophoblast (inner layer)
- Syncytiotrophoblast
- —–>will invade and displace decidual cells of the endometrium to embed
Where do lacunae appear?
syncytiotrophoblast layer
–>will eventually fuse together and fill with blood and uterine secretions
What is the primordial uteroplacental circulation?
oxygen and nutritive substances pass to embryo via diffusion through lacunar networks
Give the timeline for implantation
- Zona pellucida degen (Day 5)
- Blastocyst adheres to endometrial epithelium (Day 6)
- Trophoblast diff (day 7)
- Blood-filled lacunae appear in syncitiotrophoblast (day 9)
- Lacunar networks form via fusion (days 10-11)
- Syncytiotrophoblast erodes endometrial BV to establish uteroplacental circulation (days 11-12)
- Primary chorionic villi develop (days 13-14)
What are sx of ectopic pregnancy?
ap
amenorrhea
vaginal bleeding
rupture of oviduct wall
Where do ectopic pregnancies take place?
implant outside of uterine cavity, most of the time in the oviduct
–>ampulla or isthmus
What makes up the chorionic sac?
- extraembryonic somatic mesoderm
- cytotrophoblast
- syncytiotrophoblast
What surrounds the amnion and primary umbilical vesicle?
extraembryonic mesoderm
What mesoderm lines the trophoblast and covers the amnion?
extraembryonic somatic mesoderm
What mesoderm surrounds the umbilical vesicle?
extraembryonic splanchnic mesoderm
What is the fluid-filled cavity that surrounds the amnion and umbilical vesicle?
extraembryonic coelom
What is a thin, tough membrane that surrounds the fetus and amniotic fluid?
amnion/amniotic sac
–>amnioblast separates from epiblast to enclose amniotic cavity
What eventually obliterates the chorionic cavity and forms the epithelial covering of the umbilical cord?
amnion
What is amniotic fluid derived from?
maternal tissue and IF initially
- ->fetal urinary system secretes @ 11 weeks
- ->resp and GI tract contribute
exchange @ umbilical cord
Describe hydraminos
excessive amniotic fluid
- ->genetic defect d/t CNS or blockage of GI tube
- ->abd pain, sig swelling or bloating, breathlessness
Describe oligohydraminos
insufficient amniotic fluid (<400mL)
- ->renal agenesis or pulmonary hypoplasia
- ->d/t placental abnormality or maternal HBP
not enough cushion for fetus and umbilical cord
What obliterates the uterine cavity?
when the decidua capsularis (covering chorionic surface) bulges into the uterine cavity and fuses with the decidua parietalis on the opposite wall
–>amniochorionic membrane
What forms from the decidua capsularis degeneration?
@ 22-24 weeks
makes smooth chorion that fuses with parietalis–>amniochorionic membrane
Where is the amniochorionic membrane?
fusion with decidua capsularis and adheres to parietalis
–>formed d/t amniotic sac grows faster than chorionic sac and obliterates uterine cavity
What forms chorionic villi?
proliferation and projection of cytotrophoblast into syncytiotrophoblast
What is the cytotrophoblastic shell?
chorionic villi that attach to the decidua basalis
- ->anchors chorionic sac to decidua
- ->A/V pass freely through gaps in shell to enter intervillous space where exchange occurs
What does placental development involve?
formation of chorionic villi from the chorionic sac
proliferation of cytotrophoblasts
What makes up the placenta?
decidua basalis
villous chorion
What are primary chorionic villi?
cytotrophoblasts that grow into syncytiotrophoblast layer
–>1st stage of placental development @ end of 2nd week
What do villi that are assicated with the decidua capsularis become?
compressed–>degenerate to form smooth chorion (surrounds fetus except at villousu chorion)
What do villi associated with the decidua basalis become?
rapidly increase and branch
–>forms villous chorion, a bushy area of the chorionic sac that connects with umbilical cord
What surrounds the chorionic sac, attaches and erodes decidua basalis and creates an intervillous space?
cytotrophoblastic cell
–>lacuna b/t villi make intervillous space
What divides villous chorion into irregular convex areas?
placental septa via decidual erosion
What are irregular convex areas of the villous chorion called?
cotyledons
–>projections that contain chorionic villi, between decidua basalis and intervillous space
What is in the intervillous space of the placenta?
maternal blood (11-14 weeks)
What villi extend from the chorionic plate into intervillous space?
main stem villi
What villi extend from the main stem villi to increase surface area?
Branch villi
What villi attach to the maternal tissues through the cytotrophoblastic shell?
anchoring villi
What do cotyledons contain?
- 2+ main stem villi
- multiple branch villi
What are secondary chorionic villi?
extraembryonic mesoderm grows into primary villi
–> NO BV
mesoderm core, cyto, syncytio
What are tertiary chorionic villi?
extraembryonic mesoderm diff into capillary and RBC
- ->capillary and CT coore
- ->cyto
- ->syncytio
What villi are the main sites for exchange of maternal and fetal blood?
branch villi
What is the difference in makeup of placental membrane before and after 20 weeks?
before 20: cytotrophoblast included with syncytio, CT in villi and capillary endotheliym
after 20: extremely diminished cytotrophoblast layer
What does NOT cross the placenta?
protein hormones
–>insulin pituitary hormones
bacteria
drugs with AA-like structures
—>methyldopa
Where is the umbilical cord attached?
near center of fetal surface of placenta
What forms the umbilical cord?
connecting stalk covered with amnion
--> 2 umbilical As
DEOX
--> 1 umbilical V
OXDescribe absence of umbilical A
common
—>chromosomal and fetal abnormalities
detected via US
Describe placenta previa
placenta implants in lower uterine segment or cervix
–>3rd trimester bleeding, most common type of abnormal placenta
Describe placenta accrete
partial or complete absence of decidua, so villous chorion attaches directly to myometrium
–>placenta doesn’t separate at birth
–>severe postpartum bleeding
Describe a partial hydatidiform mole
portion of normal villi become edematous
- ->fetal tissue found
- ->normal ovum via 2 sperm
triploid or tetrapliod karyotypes
Describe complete hydatidiform mole
all villi enlarged no fetal tissue fertilized empty ovum --->all DNA paternal --->fertilized by duplicated sperm
46XX or 46XY
Describe an invasive mole
Complete mole penetrates or perforates uterine wall
- ->HIGH blood levels hCG
- ->can cause hemorrhaging d/t invasion
- ->chemotherapy
Describe gestational choriocarcinoma
Highly invasive, met tumor via trophoblast cells
–>50% of mole pregnancies
–>increasing hCG titer without uterine enlargement
–>combined chemotherapy
What type of twin originates from 2 zygotes?
dizygoitc=fraternal
What is the relationship between zygotic splitting of twins and membranes?
earlier the split, the more separate the membranes and placentas
What are the membranes and placental relationships of dizygotic twins?
Separate amnion, chorion and placentas
What membranes arise if monozygotic twins separate at the 2-8 cell stage (up to 72 hrs)?
Diamniotic
Dichorionic
–>fused or separate placenta
What membranes arise if monozygotic twins separate at the blastocyst stage (4-8 days)?
Diamniotic
Monochorionic
What membranes arise if monozygotic twins separate at the implant stage (9-12 days)?
Monoamniotic
Monochorionic
Why do you have conjoined twins?
separate way late, past implant stage
What are 65% monozygotic twins?
division of embryoblast of blastocyst
–>1 placenta, 1 chorionic sac, 2 amniotic sacs
What are 35% monozygotic twins?
division of morula of blastocyst
–> 2 blastocysts with own amniotic and chorionic sacs
What’s the difference between the smooth and villous chorion?
Villous chorion is the fetal side of the placenta where the umbilical cord is
Smooth chorion is the rest of the sac surrounding the fetus
What ruptures during childbirth?
amniochorionic membrane
