Placental and Fetal Membranes Flashcards
What part of the blastocyst becomes extraembryonic tissue?
trophoblast
What occurs to the blastocyst when it implants?
embryoblast –> bilaminar embryonic disc
What are the extraembryonic structures present in the blastocyst?
amnion
umbilical vesicle
connecting stalk
chorionic sac
What are the 3 parts of the decidua?
decidua basalis: deep to conceptus, forms maternal part of the placenta
decidua capsularis: superficial and overlies conceptus (opposite side of implantation site, faces uterine cavity)
decidua parietalis: remaining parts
What does the decidua look like histologically?
pale-staining cells w/ glycogen and lipid accumulation
What is the decidual reaction?
cellular and vascular changes that occur as the blastocyst implants
When does implantation occur?
2nd week (6-10 days post fertilization)
What part of the endometrium is incorporated into the placenta?
functional layer
What does the trophoblast differentiate into once it contacts the endometrium?
cytotrophoblast = inner layer
syncytiotrophoblast (outer layer) –> invades and displaces decidua basalis; produces hCG
When does the zona pellucida degenerate?
day 5
When does the blastocyt adhere to the endometrial epithelium?
day 6
When does the trophoblast differentiate?
when does the syncytiotrophoblast erode endometrial tissue?
day 7
day 8
When do blood-filled lacunae apper in the syncytiotrophoblast?
When do the lacunar networks form?
day 9
days 10 and 11
When does the syncytiotrophoblast erode endo blood vessels to establish uteroplacental circulation?
When do primary chorionic villi develop?
days 11 and 12
days 13 and 14
What is the amnion?
How does it form?
thin, tough membrane that surrounds the embryo/fetus and amniotic fluid
amnio blasts separate from the epiblast –> enclose the developing amniotic cavity
What is an ectopic pregnancy and where do they most commonly occur?
implantation of plastocyst outside uterine cavity = 2% of all pregnancies
95-98% occur in oviduct, most commonly in ampulla and isthmus
produce hCG, but at slower rate than normal pregnancies
How does the amnion form?
amnioblasts separate from the epiblast –> enclose epiblast and space btw epiblast and amnion/amniotic sac = amniotic cavity
What occurs to the relative sizes of the amniotic and chorionic cavities as the embryo grows?
amniotic fluid increases and embryo grows –> amnion eventually goes out and bindw w/ chorionic sac = just chorion now
What forms the epithelial covering of umbilical cord?
amnion
What is the villous chorion?
initial villi growing out of chorion to surrounding uterus –> fetal part of placenta
What is the function of amniotic fluid?
cushions fetus inside uterus, provices space, regulates fetal body temp
derived from maternal tissue and IF
How often does the water of the amniotic fluid change itself?
every 3 hrs - exchange w/ fetal blood via umbilical cord
fluid also secreted by respiratory sys, GI tract, and urinary system
When does the fetal urinary sys excrete amniotic fluid?
11 wks
What are the amniotic fluid volumes throughout pregnancy?
10 wks - 30 mL
20 wks - 350 mL
37 wks - 700-1000 mL
What is polyhydramnios?
excessive amniotic fluid
genetic defect, fetal defect in CNS or GI blockage can cause
What is oligohydramnios?
too little amniotic fluid
problem w/ fetal development (renal agenesis, pulmonary hypoplasia)
placental abnormality or maternal HBP
What makes up the chorion?
extraembryonic mesoderm from hypoblast surrounds amnion and primary umbilical vesicle
will separate and split mesoderm into 2 layers
separated by extraembryonic coelom = fluid-filled cavity that surrounds amnion and umbilical vesicle
What are the 2 layers of chorion?
extraembryonic somatic mesoderm –> lines trophoblast and covers amnion
extraembryonic splanchnic mesoderm –> surrounds umbilical vesicle
What does the connecting stalk do?
connects amnion and umbilical vesicle to the chorion
What defines the entire chorionic sac?
extraembryonic somatic mesoderm + cytotrophoblasts + syncytiotrophoblasts
What are the fetal and maternal parts of the placenta?
fetal = villous chorion, projects into intervillous space
maternal = decidua basalis, almost entirely replaced by the fetal part of the placenta (4th month)
What is the cytotrophoplastic shell?
external layer of trophoblast cells on maternal surface that attach villi to decidua basalis
When do chorionic villi appear?
Where are they initially and how do they change?
appear week 2
cover chorionic sac until 8th week –> then degenerates
part w/out villi = smooth chorion
part w/ villi = villous chorion/chorion frondulum
What is the placental barrier?
cytotrophoblast and syncytiotrophoblast cells and supporting basal lamina
endothelial cells and basal lamina of fetal blood capillaries
Primary villi
cytotrophoblast core covered by syncytiotrophoblast
secondary villi
extraembryonic mesoderm extends into primary villi (3rd week)
mesenchyme core –> cytotrophoblasts –> syncytiotrophoblasts
tertiary villi
extraembryonic mesoderm –> capillary and blood cells
capillary core and mesenchyme–> cytotrophoblast –> syncytiotrophoblast
What are cotyledons?
rough surface of fetal part of placenta
produced when villi erode –> decidua makes placental septa –> 2 main stem villi + multiple branch villi = a cotyledon
What are stem and branch villi?
stem villi = attach to maternal tissues through cytotrophoblastic shell
branch villi = grow from sides of stem
What is the amniochorionic membrane and how does it form?
amniotic sac grows faster than chorion –> fuses w/ capsularis –> decidua capsularis degenerates 22-24 weeks –> smooth chorion will merge with decidua parietalis = amniochorionic membrane
What is the timeline/character of the placental membrane?
until 20th week: syncytio, cyto, CT of villi, and fetal capillary endothelium
after 20th week: cytotrophoblasts are essentially lost; vasculosyncytial placental membrane
3rd trimester: nuclei in syncytio aggregate to form multinucleated protrusions = syncytial knots
end of pregnancy: eosinophilic firin thickens
What is the vasculosyncytial placental membrane?
cyncytiotrophoblasts directly in condact w/ endothelium of fetal capillaries
occurs after ~20th week of pregnancy
What things can cross the placental membrane?
hormones
IgG
waste products
most drugs
viruses
nutrients for baby
What things can NOT cross the placental membrane?
protein hormones
IgD, IgM, IgE, IgA
drugs w/ structural similaries to AAs
heparin
bacteria
What is the trophoectoderm shell?
What does it look like histologically?
cytotropho + outer syncytio cells in early placenta
syncytiotrophoblast cells: fusion of many cells - have many nuclei/cell w/ no discernable lateral boundary
cytotrophoblast cells: clearly demarcated w/ single, large nucleus and basophilic cytoplasm
What are hofbauer cells?
phagocytic cells predominant in early pregnancy
What are syncytial knots?
aggregates of syncytiotrophoblast nuclei
in late placenta
What is a fibrin/oid?
amorphous eosinophilic substance commonly deposited in interillus space in older placenta
clings to villus surface and may bind several villi together
commonly used for placental stagin
What is contained in the umbilical cord?
2 umbilical arteries (baby–> mom)
1 umbilical vein (mom –> baby)
What are the 3 main circulatory shunts?
ductus venosus –> skips liver
ductus arteriosus and foramen ovale –> skip lungs
What is placenta accreta (in general)?
abnormally strong and deep attachment of placenta to uterine wall
due to previous uterine surgery or scare tissue from curettage
incidence increases w/ increasing C-section rate
What are the 3 types of placental acretta?
placenta accreta: through uterine wall, but doesn’t penetrate myometrium (75%)
increta: through myometrium (15%)
percreta: through serosa, commonly attaches to bladder/rectum (10%)
What are the 3 types of placental previa?
marginal: margin of placenta lies close to internal uterine os
partial: edge of placenta extends across part of internal os
total: placenta covers internal os
What is a hydatidiform mole?
replacement of normal villi by dilated or hydropic translucent vesicles
caused by improper fertilization (polyspermy)
What are the 2 types of hydatidiform mole?
partial: triploid w/ one set of maternal chromosomes and 2 paternal; from meiotic nondisjunction or polyspermy; capillaries w/ blood seen in villi
complete: of paternal origin, no recognizable fetus; blighted ovum fertilized by haploid sperm –> reduplicates in egg; avascular villi w/ no blood in vessels
What is an invasive mole?
complete hydatidiform mole w/ increased local invasion
persistent high hCG
trophoblast deeply invades uterine wall and can cause hemorrhaging
responsive to chemo
What is choriocarcinoma?
invasive, metastatic tumor that arises from gestational chorionic epithelium
50% of ppl with molar pregnancies
increasing hCG w/ no uterine enlargement
combination chemo is usually curative
What are the membranes like in dizygotic twins?
2 amnions and 2 chorions
chorions and placentas may be fused if implantation occurs near each other
What happens if monozygotic twins are divided in the embryoblast stage?
one placenta
one chorionic sac
two amniotic sacs
*placental vessels may or may not anastomose
What happens if monozygotic twins separate in embryonic blastomere stage?
2 amnions
2 chorions
2 separate placentas (but can fuse if them implant closely)
