39. Placenta and Fetal Membranes Flashcards
What are the 4 fetal membranes?
Chorion
Amnion
Umbilical vesicle
Allantois
What separates the fetus from the endometrium?
The placenta + 4 fetal membranes
Describe the stem cell ability of the zygote
Totipotent
Expression of cell lineage specific factors begins in the blastocyst:
The ______ becomes the embryo
The _____ becomes the extra-embryonic tissue (i.e., the fetal membranes)
Embryoblast
Trophoblast
What are the 2 parts of the trophoblast layer?
Polar (in direct contact with embryoblast)
Mural (surrounding blastocyst cavity)
In what week of development does blastocyst implantation occur
2nd week
When implantation occurs during the second week of development, the embryoblast becomes the ________, composed of the _______ + _________, the former is what forms the primary germ layers
Bilaminar embryonic disc; epiblast + hypoblast
As implantation takes place, the trophoblast contacts the endometrium, at which time it differentiates into an inner layer called the _____ and an outer layer called the ____ which is what invades and displaces the _____ cells of the endometrium
Cytotrophoblast; syncytiotrophoblast; decidual
The syncytiotrophoblast produces _____, which enters maternal circulation via the _______ network
hCG; lacunar
95-98% of ectopic pregnancies occur in the ____ or _____ of the uterine tube
Ampulla; isthmus
Signs/symptoms of ectopic pregnancy
Abdominal pain
Amenorrhea
Vaginal bleeding
Rupture of oviduct wall
Do ectopic pregnancies produce hCG?
Yes, but at a slower rate than normal pregnancies
The ______ is the thin, tough membrane that surrounds the embryo/fetus and amniotic fluid
Amnion
The amniotic sac forms when amnioblasts separate from the _____ and enclose the developing amniotic cavity; the amnion is then considered continuous with cells of the layer from which it was derived
Epiblast
With development of the amnion, there is development of ______ _____ circulation, supplying O2 and nutritive substances via diffusion through lacunar networks
Primordial uteroplacental
The amnion itself will grow into and eventually obliterate the _____________, as well as form the epithelial covering of the ______
Chorionic cavity; umbilical cord
What is the function of amniotic fluid
Cushions fetus inside uterus, provides space for fetal movement, regulates fetal body temp
[made up of organic proteins, carbs, fats,enzymes, and hormones, as well as inorganic salts, ions, glycophospholipids, steroid hormones]
What is amniotic fluid derived from
Maternal tissue
Interstitial fluid
What are volumes of amniotic fluid like from 10 weeks — 20 weeks — 37 weeks?
10w = 30 mL 20w = 350 mL 37w = 700-1000 mL
[water content changes every 3 hrs, exchange with fetal blood via umbilical cord — ‘dialysis’; fluid secretion from respiratory and GI tracts, as well as fetal urinary system at 11 wks]
Excessive amniotic fluid characterized by abdominal pain, significant swelling/bloating, and breathlessness
Hydramnios
Insufficient amniotic fluid (<400 mL) in which decreased fluid does not provide enough cushion to fetus and umbilical cord — leads to defects in lung dev’t, clubbed extremities, etc.
Oligohydramnios
What causes hydramnios vs. oligohydramnios?
Hydramnios = genetic defect, fetal defect in CNS, or blockage of GI tube
Oligohydramnios = problem with fetal development (renal agenesis, pulmonary hypoplasia), placental abnormality, or maternal HTN
The amnion forms from epiblast. The chorionic sac forms from ___________, which is from __________
Extraembryonic mesoderm; hypoblast
In the formation of the ________, the extraembryonic mesoderm from the hypoblast surrounds the amnion and primary umbilical vesicle (yolk sac), later separating and splitting the mesoderm into 2 layers. These are separated by the __________, a fluid-filled cavity that surrounds the amnion and umbilical vesicle.
Chorionic sac; extraembryonic coelom
For the chorionic sac, ________ ________ _____ lines the trophoblast and covers the amnion while _____ _____ _____ surrounds the umbilical vesicle
Extraembryonic somatic mesoderm; extraembryonic splanchnic mesoderm
During formation of the chorionic sac, the amnion and umbilical vesicle are attached to the chorion via the _____ _____. Also around this time, the primary vesicle will pinch off, thus forming the secondary umbilical vesicle which is now known as the _____ ____
Connecting stalk; yolk sac
Overall, the chorionic sac is composed for what 3 parts?
Extraembryonic somatic mesoderm
Cytotrophoblasts
Syncytiotrophoblasts
The chorionic villus originates from the chorionic plate and derives from a ____ ____, giving rise to villous branches
Fetal vessels are spearated from the maternal blood in the intervillous space by the ____ ______, made up of cytotrophoblast and syncytiotrophoblast cells and supporting basal lamina, as well as endothelial cells and basal lamina of fetal blood capillaries
Stem villus
Placental barrier
Each chorionic villus has a core of _______ CT and fetal ____ ____
Mesenchymal; blood vessels
During what week of development do chorionic villi first appear?
Appear by end of 2nd week
Chorionic villi consist of chorionic processes that form vascular syncytial columns. These will grow into ______, likely induced by _________
Syncytiotrophoblasts; extraembryonic somatic mesoderm
Chorionic villi projections form the primary chorionic villi in the first stage of placental development. They will cover the entire chorionic sac until the ____ week
8th
Functional layer of the endometrium that separates from the remainder of the uterus after parturition
Decidua
What are the 3 parts of the decidua
Decidua basalis — deep to the conceptus, forms the maternal part of the placenta
Decidua capsularis — superficial and overlies conceptus
Decidua parietalis — remaining parts of the decidua
How does the decidua appear on histological slides?
Pale-staining cells with glycogen and lipid accumulation
Fetomaternal organ responsible for protection, nutrition, respiration, excretion of waste, and hormone production
Placenta
Compare/contrast the fetal part vs. the maternal part of the placenta
Fetal part = formed by the villous chorion, which projects into the intervillous spcae containing maternal blood
Maternal part = formed by decidua basalis, almost entirely replaced by the fetal part by 4th month
Primary chorionic villi cover the entire chorionic sac until the 8th week. With growth, the villi associated with the ____ ____ become compressed, blood supply is reduced, and these villi with degenerate, leaving an avascular bare area known as the ____ ____
Decidua capsularis; smooth chorion
While the villi associated with the decidua capsularis degenerate, those associated with the ___ ____ rapidly increase, branching profusely, and enlarging to form the bushy area of the chorionic sac known as the ____ ____
Decidua basalis; villous chorion
The chorionic villi invade the decidua basalis and erode the decidual tissues, forming the _____ _____
This erosion produces the ____ ____ which divide the fetal part of the placenta into irregular convex areas called _______
Intervillous space
Placental septa; cotyledons
Cotyledons consist of what components?
2+ main stem villi and multiple branch villi
What is the difference between stem villi and branch villi?
Stem villi = attach to maternal tissues through cytotrophoblastic shell
Branch villi = grow from sides of stem villi — participate in gas exchange
What layer of the decidua bulges into the uterine cavity and forms the capsule covering the surface of the chorionic sac as the embryo/fetus enlarges?
Decidua capsularis
The decidua capsularis forms the capsule covering the surface of the chorionic sac as the embryo enlarges. The capsularis thins and fuses with the ______ on the opposite wall, eventually obliterating the ______ _____
Decidua parietalis; uterine cavity
The decidua capsularis degenerates around 22-24 weeks, then the ______ _____ will fuse with the decidua parietalis, obliterating the uterine cavity
Smooth chorion
The amniotic sac grows faster than the chorionic sac, so these eventually fuse forming the ________ _____
What is the fate of this structure?
Amniochorionic membrane
This membrane will fuse with the decidua capsularis and adhere to the parietalis
Primary villi form at the end of the 2nd week; cytotrophoblast cells proliferate due to extraembryonic mesoderm and extend forming villi. The core of the cytotrophoblast cells is covered by the syncytiotrophoblast.
The secondary villi form when the _____ ______ extends into the primary villi during the 3rd week.
What are the 3 layers of the secondary villi?
Extraembryonic mesoderm
[core of extraembryonic mesoderm, middle cytotrophoblast layer, outer syncytiotrophoblast layer]
Tertiary villi develop when extraembryonic mesoderm differentiates into ____ and _____ cells
What are the 3 layers of tertiary villi?
Capillary; blood
Core of extraembryonic mesoderm + CAPILLARIES, middle cytotrophoblast layer, outer syncytiotrophoblast layer
What is the primary difference between secondary and tertiary villi?
Secondary villi DO NOT have capillaries but tertiary DO
What condition can occur with reduced development of the branches of the chorionic villus tree?
Preeclampsia
______ chorionic villi are bathed in maternal blood and are the site of main exchange
They provide a large surface area for materials exchange across the _______ membrane, which is a composite structure consisting of extra-fetal tissues separating maternal and fetal blood
Branch
Placental
What is the difference in placental membrane structure until the 20th week, and after the 20th week?
Up until the 20th week, composed of syncytiotrophoblast, cytotrophoblast, connective tissue of villi, and endothelium of fetal capillaries
After 20th week, composed for syncytiotrophoblast, connective tissue of the villi, and endothelium of fetal capillaries — cytotrophoblasts are essentially lost, membrane can be markedly thin
After the 20th week, the syncytiotrophoblast of the placental membrane is in direct contact with the endothelium of fetal capillaries, forming the ____ _____ membrane
Vasculosyncytial placental
In the 3rd trimester, nuclei in the placenta - in the syncytiotrophoblast - aggregate to form multinucleated ____ ___
Syncytial knots
Toward the end of pregnancy, eosinophilic ________ thickens on surface of villi
Fibrin/oid
Compare/contast histology of the placenta on fetal side vs. maternal side
Fetal side = smooth and associated with amnion
Maternal side = partially subdivided into 10+ lobes by decidual septa; each lobe contains 10+ stem villi and its branches
In the early placenta, the _______ shell is comprised of inner cytotrophoblast and outer syncytiotrophoblast cells
Describe these cell populations in terms of histology
Trophectoderm
Cytotrophoblast cells = clearly demarcated, with single large nucleus and basophilic cytoplasm forming complete ring around each villus
Syncytiotrophoblasts = result from fusion of many cells and have many nuclei/cell with no discernable lateral boundaries
In the early placenta, the core of villus is comprised of mesenchymal cells (fibroblasts) and fetal blood vessels.
______ cells are phagocytic cells predominant in early pregnancy
Fetal RBCs are in early stages of _______, so they can still have nuclei
Hofbauer
Hematopoiesis
In the late placenta, multinucleate syncytiotrophoblast cells form trophectoderm shell (after 4th month of pregnancy, cytotrophoblast cells decrease/essentially non-existent)
What 3 structures distinguish the late placenta from the early?
Hofbauer cells = macrophage like cells found within CT core
Syncytial knots = aggregates of syncytiotrophoblast nuclei
Fibrinoid = amorphous eosinophilic substance commonly deposited in intervillous space in older placenta — clings to villus surface and may bind several villi together, frequently used for placental staging
The umbilical cord contains 2 ______ and 1 ________
What is the oxygenation of these vessels?
Umbilical arteries; umbilical vein
Vein carries 80% oxygenated fetal blood
Arteries return deoxygenated fetal blood to placenta
What are the 2-3 main fetal circulatory shunts?
Ductus venosus (bypasses the liver)
Ductus arteriosus and foramen ovale (bypasses the lungs)
Condition characterized by abnormally strong and deep attachment of the placenta to uterine wall — can be d/t previous uterine surgery or scar tissue following uterine curettage
Placental accreta
What are the 3 forms of placental accreta?
[based on how deeply the myometrium is penetrated]
Placenta accreta = placenta invades uterine wall but does not penetrate the myometrium (~75% of cases)
Placenta increta = placenta penetrates through myometrium (~15% of cases)
Placenta percreta = placenta extends through uterine wall and pierces uterine serosa, commonly attaches to bladder and/or rectum (~10% of cases)
Abnormal extension of placenta over or close to internal opening of cervical canal
Placental previa
3 types of placenta previa
Marginal = margin of placenta lies close to internal cervical os
Partial = edge of placenta extends across part of internal ostium
Total = placenta covers internal cervical ostium
What is the primary complication associated with placenta previa?
Spontaneous painless bleeding, resulting from partial separation of placenta from uterus
Gestational trophoblastic disease in which replacement of normal villi by dilated or hydropic (edematous) translucent vesicles occurs
Hydatiform mole
Describe partial hydatiform mole
Fetus commonly found, usually 69,XXY: one haploid set of maternal chromosomes (23,X) and 2 haploid sets of paternal chromosomes (46,XY)
Arises from meiotic nondisjunction or from 2 haploid fertilizing sperm
Capillaries containing blood can be seen in the villi
Describe complete hydatidiform mole
Of paternal origin (androgenetic), no recognizable fetus
Fertilization of a blighted ovum by a haploid sperm, reduplicates within egg
Frequent karyotype = 46,XX or 46,YY
Avascular villi with no blood present in remnant vessels
Describe an invasive hydatidiform mole
Complete mole with increased local invasion
Diagnosed by persistent high blood levels of hCG
Trophoblast deeply invades uterine wall and can cause hemorrhage
Responsive to chemo
Highly invasive, metastatic tumor that arises from gestational chorionic epithelium, observed in about 50% of patients with molar pregnancies; increasing hCG titer w/o uterine enlargement
Tx with combined chemotherapy is usually curative
Choriocarcinoma
Fetal membranes and placentas vary according to origin of twins
_______ twins always have 2 amnions and 2 chorions, but chorions and placentas may be fused
In ______ twins, the type of placenta and membranes formed depends on when the twinning process occurs — division of ______ vs. ________ (2-8 cell stage)
Dizygotic
Monozygotic; embryoblast; embryonic blastomeres
What nutrients cross the placenta?
Water Glucose Electrolytes Amino acids Vitamins
What hormones cross placenta?
Testosterone
Progestins
Thyroxin
Triiodothyronine
Which of the following cross the placenta?
IgG, IgM, IgA, IgD, IgE
IgG ONLY!
What waste products cross the placenta?
Urea
Uric acid
Conjugated bilirubin
T/F: most drugs cross the placenta including alcohol, cocaine, and heroine
True
What infectious agents cross the placenta?
CMV, Rubella, Coxsackiviruses
Variola, measles, herpes
Treponema pallidum (syphilis); toxoplasma gondii, listeria monocytogenes
