Placenta and fetal membranes Flashcards
what are all the fetal membranes?
Chorion
amnion
umbilical vesicle
allantois
What is the function of the Placenta? and what are its two components
the Placenta is a fetomaternal organ whith two components
- fetal part = chorionic sac (outermost fetal membrane)
- Maternal part = derived from endometrium
Exchange of nutrients and O2 occurs between the maternal and fetal blood streams via the placenta
Vessels in the umbilical cord connect the placental circulation with the fetal circulation
what are the extraembryonic structures?
Amnion
umbilical vesicle
connecting stalk
chorionic sac
what are the three layers of the decidua? and what is it?
Functional layer of the endometrium that separates from the remainder of the uterus after parturition
-pale staining cells with glycogen and lipid accumulation
Decidua basalis: deep to the conceptus. forms that maternal part of the placenta
Decidua capsularis: superficial and overlies the conceptus
Decidua parietalis: remaining parts of the decidua
8 step summary of implantation
1) implantation of the blastocyst in the uterine endometrium begins at the end of the 1st week, completed by the end of the 2nd week
2) Zona pellucida degenerates at day 5 due to enlarging of the blastocyst and enzymatic lysis
3) Blastocyst adheres to the endometrial epithelium (day 6)
4) trophoblast differentiates into two layers, the syncytiotrophoblast and the cytotrophoblast (day 7)
- syncytiotrophoblast erodes endometrial tissues and blastocytes begins to embed in the endometrium day 8
5) Blood filled lacunae appear in the syncytiotrophoblast at day 9
6) Lacunar networks form by fusion of adjcent lacunae at days 10 and 11
7) Syncytiotrophoblasts erodes endometrial blood vessels allowing maternal blood to seep in and out of lacunar networks and establishing uteroplacental circulation at days 11 and 12
8) Primary chorionic villi develop at days 13 and 14
What is an ectopic pregnancy and what are some signs?
Implantation of blastocyte outside the uterine cavity
-most occur in the oviduct in the ampulla or the isthmus
signs:
- abdominal pain
- amenorrhea
- vaginal bleeding
- rupture of the oviduct wall
- affected tube/conceptus usually surgically removed
what is the chorionic sac? and how does the extraembryonic, somatic, splanchnic and coelom mesoderm interact with the chorionic sac?
Chorionic sac is the extraembryonic somatic mesoderm plus the cytotrophoblasts and the syncytiotrophoblasts
Extraembryonic mesoderm (from hypoblast) surrounds the amnion and primary umbilical vessivel
Extramembryonic somatic mesoderm lines the trophoblast and covers the amnion
extraembryonicsplanchnic mesoderm surrounds the umbilical vesicle
extraembryonic coelom is the fluid fillded cavity that surrounds the amnion and umbilical vesicle
What is the amnion?
Amnion (amnionic sac) is a thin though membrane that surrounds the embryo and fetus that is filled with amniotic fluid
amnioblasts separate from the epiblast and then eclose the developing amniotic cavity
what is amniotic fluid and its main functions?
Initially derived from maternal tissue and intersitial fluid
- fetal urinary system will excrete amniotic fluid
- Respiratory system and GI will also excrete
- done via a dialysis likeexchange via umbilical cord
Functions to cushion the fetus and permits fetal movements and regulat the fetus body temperature
- organic compounds (proteins, carbs, fats, enzymes, hormones)
- inorganic salts, ions, glycophospholipids, and steriod hormones
Hydramnios?
Excessive amniotic fluid
Genetic defect, a fetal defect in the central nervous system or blockage of the gastrointestinal tube
Clinical signs include abdominal pain or bloating and breathlessness
oligohydramnios?
insufficient amniotic fluid that is less than 400 mL
Problem with the fetal development due to renal agenesis or pulmonary hypoplasia
Placental abnormality or maternal High blood pressure
Decreased fluid does not provide enough cushion to fetus and umbilical cord
formation of the amnion/chorionic sac
Decidua capularis forms capsule covering surface of the chorionic sac
Embryo will enlarge causing the decidua capularis to bulge into the uterine cavity where it thins and fuses with the decidua parietalis on the opposite wall and obliterates the uterine cavity
Amniotic sac grows faster than the chorionic sac and the they will fuse forming the amniochorionic membrane
what are the two components of the Placenta? and 2 steps to the development of the placenta
Fetal part which is the villious chorion that projects into intervillous space that contains maternal blood
Maternal Part: decidua basalis, endometrium deep to conceptus
Placenta development involves
- formation of chorionic villi (from chorionic sac)
- Proliferation of the cytotrophoblasts
Forming of the primary chorionic villi? and what forms the smooth and villous chorion
Chorionic processes of the cytotrophoblasts that grow into the syncytiotrophoblast layer that form vascular syncytial columns
-appearance marks 1st stage of placental development at end of the 2nd week
will cover the chorionic sac until the 8th week
-villi associate with the decidua capsularis becomes suppressed and degenerate to smooth chorion
Villi associated with the decidua basalis rapidly increase and branch profusely and form buschy area of the chorionic sac the villous chorion
initial process of the forming of the placenta
Cytotrophoblasts of chorionic villi proliferate at chorionic plate
extend through the syncytiotrophoblasts forming the cytotrophoblastic shell
- surrounds the chorionic sac
- attaches and erodes the decidua basalis
- creates the intervillious space
what does the intervillious space derive from? and what is in it?
lacunase that developed from the invading syncytiotrophoblasts during the 2nd week
Maternal blood is in the intervillious space at the 11-14 week mark and this is when the villious chorion (fetal) and the decidua basalis (mother) are now fused
what makes the placental septa and what is its function?
Decidual erosion produces the placental septa which divides the chorion into irregular convex areas or cotyledons
difference between a Main stem, branch, and anchoring villi and what are found in a cotyledons?
Main stem villi: extending from chorionic plate
Branch villi: extend from a main stem villus to increase the surface area
anchoring villi: villi that attach to the maternal tissues through the cytotrophoblastic shell
in the cotyledons they contain 2 plus main stem villi and multiple branch villi
what is the difference between a primary, secondary, and tertiary villi?
Primary villi: cytotrophoblasts are covered by syncytiotrophoblasts
Secondary villi: extra embryonic mesoderm that grows into a primary villi (3rd week)
- extraembryonic mesoderm core
- cytotrophoblasts
- syncytiotrophoblasts
Tertiary villi: extraembryonic mesoderm defferentiates into capillary and blood cells
- capillaries and CT core
- cytotrophoblast layer (middle)
- syncytiotrophoblasts layer (outer)
- secondary villi do not have capillaries but tertiary do
what occurs after 20 weeks at the placental membrane?
they will no longer contain cytotrophoblasts
but will still have syncytiotrophoblasts, CT with villi, and capillary endothelium
what is and isnt transferred across the placenta?
Can cross:
- nutrients: water, glucose, electrolytes, AA, and vitamins
- Hormones: testosterone, progestins, thyroxin, and T3
- igG antibodies
- Waste products: urea, uric acid, conjugated billirubin
- drugs: most do, alcohol, cocaine, heroin, labor inducing drugs
- infectous agents: cytomegalovirus, rubella, varicella, measles, herpes, syphillis
do not cross the placenta:
- protein hormones: insulin pituitary hormones
- bacteria
- drugs with amino acid like structures (methyldopa)
what makes up the umbilical cord? and what if it is gone?
connecting stalk is enveloped by the amino as it enlarges forming cord
Two umbilical arteries carrying deoxygenated fetal blood away
one umbilical vein carrying 80% oxygenated fetal blood toward
absence of umbilical cord:
- chromosome or fetal abnormalities
- agenesis or degeneration of one of the two umbilical arteries
- detected before birth by ultrasonography
Placenta previa and the 4 different types?
Placenta implants in lower uterine segment or cervix
- often leading to serious 3rd trimester bleeding
- 20% of all cases of bleeding is due to this
- most common type of abnormal placentation
Total placenta previa = covering all of cervix os
partial placenta previa = covering some of cervix os
marginal placenta previa = close to cervix os
low implatation previa = near cervix os
Placenta accretea?
Partial or complete absence of the decidua therefore villous chorion adheres directly to myometrium
- failure of placental separation at birth
- can cause severe bleeding and possibly postpartum bleeding
what is hydatidiform mole and the two types?
Replacement of normal villi by dilated hydropic translucent vesicles
Partial mole:
- portion of villi are edematous and capillaries can be seen in the villi
- fetal tissue commonly found
- normal ovum fertillized with two sperm
- triploid (69,XXY) or tetraploid (92,XXXY) karyotype
Complete mole:
- most villi are enlarged covered with trophoblast invasion
- no fetal tissue
- fertiliation of blighted ovum = all DNA is paternal
- fertilized by two sperm and duplication of a single sperm
- kayotype of 46 XX or 46 XY
Invasive mole
Gestational trophoblastic disease
Complete mole that penetrates or even perforates the uterine wall
Diagnosed by persistent high blood levels of hCG
trophoblast deeply invades the uterine wall and can causehemorrhaging
responsive to chemotherapy
Gestational carcinoma?
gestational trophoblastic disease
highly invasive, metatastic tumor that arises from trophoblast cells
observed in about 50% of patients with molar pregnancies
increasing hCG titer with no uterine enlargement
treatment with combined chemotherapy agents is usually curative
Dizygotic twins
originat from two zygotes, 2 amnions and chorions due to separate implantations
relationships of amnions and chorions are dependent on how the blastocysts implant
Monozygotic twins
originate from one zygote
membranes in monozygotic twins are dependant upon timing of the division
the earlier the split the more separate the membranes and placentas will be
Time of cleavage, nature of membrane for monozygotic twins: 2-8 cell stage
timing of clevage: 0-72 hour
nature of membranes: Diamniotic, Dichorionic
35 percent of monozygotic develop from this stage of 2 cell or morula to produce 2 identical blastocytes
each embryo develops its own amniotic and chorionic sac
Time of cleavage, nature of membrane for monozygotic twins: Blastocyst
timing of cleavage: 4-8 days
nature of membranes: Diamniotic
monochorionic
65 percent of monozygotic twins develop form this stage of division
Time of cleavage, nature of membrane for monozygotic twins: implanted
time of cleavage: 9-12 days
nature of membranes: Monoamniotic
Monochorionic
potential for conjoined twins
