Download - The Placenta and Fetal Membranes
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PRESENTED BY LT COL(BILQEES)
The Placenta and Fetal Membranes
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Fetal Tissues of the Fetal-Maternal Communication System
The extravillous and villous traphoblasts Placental arm
The fetal membranes (the amnion-chorion leave) Paracrine arm
Human placenta : hemochorioendothelial type
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Early Human Development
ZygoteBlastomeresMorulaBlastocystEmbryoFetusConceptus
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Fertilization of the Ovum and Cleavage of the Zygote
Moore, fig3-5
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58-cell blastocyst107-cell blastocystFig 5-1
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Implantation Moore, fig 3-4
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Biology of trophoblast Trophoblast is the most variable in structure,
function and development invasiveness provides for attatchment of blastocyst to
decidua of uterine cavity nutrition of the conceptus function as endocrine organ in human pregnancy
essential to maternal physiological adaptations & maintenance of pregnancy
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Differentiation Cellular, syncytial/ uninuclear , multinuclear
Formation of the Syncytium
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Cytotrophoblasts are the cellular progenitors of the syncytiotrophoblast
Cytotrophoblas
tSyncytiotrophoblast
Morphologically uninuclear cells multinuclear giant cells
cell boders well demarcated lacking
nucleus single, distinct multiple & diverse
miotic figure present absent
Origin germinal cell cytotrophoblast
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after apposition & adherence, intrusion of cytotrophoblast between endometrial epithelial cells this process is facilitated by degradation of the
extracellula matrix of endometrium /decidua catalyzed by urokinase-type plasminogen activator urokinase plasminogen activator receptor multiple metalloproteinase
These functions of cytotrophoblasts invading the endometrium are indistinguishable from those of metastasizing malignant cells
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Immunological Acceptance of the Conceptus
Previous Theories antigenic immaturity of the embryo-fetus diminished immunological responsiveness of
the pregnant woman Decidua : immunologically privileged tissue site
The acceptance and the survival of conceptus in the maternal uterus must be attributed to immunological peculiarity of the trophoblasts, not the decidua
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Current Status of Research
Expression of the HLA system in trophoblast unique set of lymphocytes > may provide explanation for immunological
acceptance of the conceptus
주로 trophoblast HLA expression (monomorphic HLA-G class I) 과 uterine large granular lymphocyte (LGL) 로 설명하고 있다 . 그러나 아직은 완전하지 않다 .
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Immunocompetency of the Trophoblasts
Many researchers focused on the expression of the major histocompatibility complex (MHC) antigens in trophoblast MHC class II antigens are absent from trophoblasts at
all stages of gestation
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Trophoblast HLA Class I Expression
Normal implantation is dependent upon controlled trophoblast invasion of maternal endometrium/decidua and the spiral arteries a mechanism for permitting and then for limitting
trophoblast invasion
Such a system involves the uterine large granular lymphocytes(LGSs) and the unique expression of specific nomomeric HLA class I antigens in the trophoblasts
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HLA-I Gene Expression
HLA genes the products of multiple genetic loci of the MHC
within short arm of chromosome 6 17 class I genes have been identified
three classical genes A, B, C => major class I(a) transplantation antigens
three other class I(b) genes E, F, G => class I HLA antigen
HLA-G gene
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Uterine Large Granular Lymphocyte (LGL)
Believed to be lymphoid and of bone marrow origin and natural killer cell lineage.
Present in large numbers only at the midluteal phase of the cycle-at the expected time of implantation in the human endometrium.
Near the end of luteal phase of nonfertile ovulatory cycles, the nuclei of LGLs begin to disintegrate.
With blastocyst implantation, these cells persist in the decidua during the early weeks of pregnancy.
speculated that LGLs are involved in the regulation of trophoblast invasion.
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HLA-G Expression in Human Trophoblasts
HLA-G antigen identified only in extravillous cytotrophoblast in
decidua basails and chorion laeve not present in villous trophoblast, either in syncytium
or in cytotrophoblasts. expressed in cytotrophoblast that are contiguous with
maternal tissue (decidual cell)It is hopothesized that HLA-G is
immunologically permissive of antigen mismatch between mother and fetus.
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HLA Expression in the Human Embryo
as gestation progresses, cells from inner cell mass of blastocyst gradually develop both class I and II HLA antigen these tissuee are not in direct contact with maternal
tissue or blood
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Implantation and Integrin Switching
Apposition, adherence, then intrusion and invasion of the endometrium/decidua by cytotrophoblast(implantation) appears to be dependent upon trophoblast elaboration of specific proteinases
degrade selected extracellular matrix proteins of the endometrium/decidua
coordinated and alternating process referred to as "integrin switching“ facilitates migration and then attachment of trophoblasts
in the decidua
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Integrin one of four families of cell adhesion molecules (CAMs) cell-surface receptors that mediate the adhesion of
cells to extracellular matrix proteins
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Trophoblast Attachment in Decidua: Oncofetal Fibronectin
onfFN(oncofetal fibronectin) unique glycopeptide of the trophouteronectin molecule
trophouteronectin or trophoblast glue formed by extravillous trophoblast, including those of
chorion laeve Function
a critical role for migration and attachment of the trophoblasts to maternal decidua
facilitates separation of extraembryonic tissues from the uterus at delivery
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Embryonic and Placental Development
Early Blastocyst Trophoblast hCG Grow & expand
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Embryonic Development after Implantation
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Cytotrophoblast Invasion of Decidual Vessels
Capillary networkarteriolesSpiral arteries
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Several curious features trophoblasts in the vessels lumen do not appear to
replicate these cells are not readily dislodged by flow of blood these cytotrophoblast appear to migrate against
arterial flow and pressure no obvious adhesion of these cells one to the other invasion of maternal vascular tissue bt trophoblasts
involves only the decidual spiral arteries, not the veins
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Organization of Placenta
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Trophoblast Ultrastructure Prominent microvilli of the syncytial surface (brush
border) pinocytotic vacuoles and vesicles
absorptive and secretory placental function
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Chorionic Villi 12th day 에 처음 발생 Primary villi
proliferation of cytotrophoblast extend into syncytiotrophoblast
Secondary villi mesenchymal cord, derived from cytotrophoblast,
invade solid trophoblast column Tertiary villi
after angiogenesis occurs from the mesenchymal cores in situ
17th day 에 fetal blood vessels are functional & placental circulation 이 establish 됨 .
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Characteristic of development of H-mole some villi, in which absence of angiogenesis results
in a lack of circulation, may distended with fluid and form vesicles
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Placental Cotyledons Certain villi of the chorion frondosum extend from
chorionic plate to the decidua and serve as anchoring villi
Each of the main stem villi(truncal) and their ramifications (rami) constitute a placental cotyledon (lobe)
For each cotyledon, a 1:1:1 ratio of artery to vein to cotyledon
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Breaks in the Placental " Barrier“ Numerous findings of passage of cells between
mother and fetus in both directions ex) erythroblastosis fetalis
A few fetal blood cells are found in the mother's blood
Fetal leukocytes may replicate in the mother and leukocyte s bearing a Y chromosome have been identified in women for up to 5 years after giving birth to a son
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Placetal Size and Weight
Total number of cotyledons remains the same throughout gestation
Individual cotyledones continue to grow Placental weights vary considerably
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Placental Aging As villi continue to branch and terminal ramifications
become more numerous and smaller > volume and prominence of cytotrophoblasts decrease
As syncytium thins and forms knots > vessels become more prominent and lie closer to the
surface The stroma of the villi
in early pregnancy branching connective ts. cells are seperated by
abundant loose intercellular matrix later
stroma becomes denser, and the cells more spindly and more closely packed
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Histologic changes that accompany placental growth and aging are suggestive of increase in the efficiency of transport to and exchange to meet increasing fetal metabolic requirements decrease in thickness of the syncytium partial reduction of cytotropholastic cell decrease in the stroma increase in the number of capillaries and approximation
of these vessels to the syncytial surface
By 4 months the apparent continuity of the cytotrophoblast is broken the syncytium forms knots on the more numerous,
smaller villi
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At term Covering of villi may be focally reduced to a thin layer
of syncytium with minimal connective tissue Fetal capillaries seem to abut the tropohoblast Villous stroma, Hofbauer cells, and cytotrophoblasts are
markedly reduced villi appear filled with thin-walled capillaries
Other changes suggestive of a decrease in the efficiency for placental exchange thickening of the basement membrane of trophoblast
capillaries obliteration of certain fetal vessels fibrin deposition on the surface of villi in basal and
chorionic plates as well as elsewhere in the intervillous space
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Blood Circulation in the Mature Placenta
A section through the placenta in situ amnion → chorion→
chorionic villi → intervillous space → decidual plate → myometrium
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Fetal Circulation
2 umbilical arteries deoxygenated, or "venous-like" blood flows to the
placenta 1 umbilical vein
with a significantly higher oxygen contentHyrtl anastomosisTwo umbilical a. separate at the chorionic
plate to supply branches to the cotyledons
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The principle factors regulating the flow of blood in the intervillous space arterial blood pressure intrauterine pressure pattern of uterine contraction factors that act specifically upon the arteriolar walls
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The Amnion
Innermost fetal membrane and is contiguous with amnionic fluid
Avascular structure Provide almost all of the tensile strength of
the fetal membranes protect against rupture or tearing
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Structure
single layer of cuboidal epithelial cells basement membrane acellular compact layer fibroblast-like mesenchymal cells zona spongiosa
Missing element of human amnion smooth muscle cell, nerves, lymphatics, blood
vessels
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Development
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Amnion Cell Histogenesis Amnion epithelial cells
derived from fetal ectoderm (embryonic disc) active metabolically; synthesis of tissue inhibitos of
metalloproteinase-1
Amnion mesenchymal cells derived from the embryonic mesoderm synthesis of interstitial collagens that make up the
compact layer of the amnion highly capable of synthesizing cytokines - IL-6, IL-8,
MCP-1 increased in response to bacterial toxin and IL-1
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Anatomy
Reflected amnionPlacental amnionUmbilical amnion
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Tensile Strength
decidua and chorion laeve are quite elastic and can expand to twice normal size during pregnancy
Amnion provides the major strength of the membrane
Tensile strength of amnion resides almost exclusively in the compact layer composed of cross-linked interstial collagens I, III, and
lesser amounts of V and VI
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Metabolic Functions solute and water transport to maintain
amnionic fluid homeostasisproduces a variety of bioactive compounds
vasoactive peptides, growth factors, cytokines Amnionic Fluid
normally clear fluid that collects within the amnionic cavity increases in quantity as pregnancy advances until near term, when it normally decreases
Average volume of about 1,000 mL is found at term
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Umbilical Cord and related Structures
Development
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Structure and Function Umbilical cord, or funis
fetal umbilicus -fetal surface of the placenta diameter: 0.8 - 2.0 cm average length: 55 cm (usual length: 30 - 100 cm)
nodulation , false knot Extracellular matrix: Wharton's jelly
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