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FETAL MEMBRANES AND PLACENTABY
PROF MASOOD AHMEDMBBS, MPHIL PHD
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Relative Size of Human Conceptus
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Implantation of the Blastocyst
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Implantation of the Blastocyst
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FETAL MEMBRANES
REFRESH FEW TERMSDECIDUA BASALIS, CAPULARIS
AND PARIETALISVILLI FORMATIONCYTOTRPHOBLASTIC SHELL
FORMATIONCHORIONIC MEMBRANE
PARTSCHORION FURONDOSUM AND
CHORION LAEVEAMNIOCHORIONIC
MEMBRANE
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Embryonic Membranes
• Amnion – Epiblast cells form a transparent membrane filled with amniotic fluid– Provides a buoyant environment that protects the
embryo– Helps maintain a constant homeostatic
temperature– Amniotic fluid comes from maternal blood, and
later, fetal urine
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CYTOTROPHOBLASTIC SHELL FORMATIONPLACENTAL BARRIER/ MEMBRANE
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Embryonic Membranes
• Allantois – a small outpocketing at the caudal end of the yolk sac– Structural base for the umbilical cord– Becomes part of the urinary bladder
• Chorion – helps form the placenta– Encloses the embryonic body and all other
membranes
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AMNION WITHIN CHORION
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Placentation
• The chorion develops fingerlike villi, which: – Become vascularized – Extend to the embryo as umbilical arteries and
veins– Lie immersed in maternal blood
• Decidua basalis – part of the endometrium that lies between the chorionic villi and the stratum basalis
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• UTERO PLACENTAL CIRCULATION –12TH DAY CIRCULATION
• 4TH MONTHCHORION FRONDOSUM AND DECIDUA BASALIS• 5TH MONTHDECIDUAL SEPTA AND COTYLEDON FORMATIONCONTIOUS FLOW IN INTERVILLOUS SPACE
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PLACENTAL SURFACES
• FETAL SURFACE • CHORIONIC VESSELLS
CONVERGING TOWARDS UMBLICAL CORD
• 2-ARTERIES AND ONE VEIN• CHORION COVERED BY AMNION• ECCENTRIC ATTACHMENT OF
UMBILICAL CORD• MATERNAL SURFACE• 15-20 COTYLEDONS
• Functional type• hemochorial
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FULL TERM PLACENTA• 15-20% INNER SURFACE COVERED WITH PLACENTA• ALL THE TIME SYNCITIAL SURFACE SEPARATES THE
MATERNAL BLOOD• COTYLEDONS- CORE OF ENDOMETRIAL TISSUE COVERED
BY SYNSITIUM• 15-20 IN NUMBER• SHAPE-DISCOID• SURFACE AREA 15-20cm• THICKNESS-3cm • WEIGHT-500-600gms
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Placentation
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Placenta
• 80-100 MATERNAL ENDOMETRIALSPIRAL ARTERIES SUPPLYING VILLI
• A TOTAL 150 ML BLOOD IN PLACENTAL CIRCULATION
• REPL;ENISHES 3-4 TIMES / MINUTE• PLACENTAL BARRIER • SEPARATES MATERNAL AND FETAL BLOOD• COMPRISED OF • ENDOTHELIAL LINING OF VILLI CAPPILARIES• C.T IN VILLI• TROPHOBLASTIC LAYER• CYTO TROPHOBLAST LAYER• 4TH MONTHS ONWARD• INCREASED EXCHANGE BY• C.T AND TROPHOBLAST LAYER DISAPPEAR
• CLOSE TO END OF PREGNANCY
• DECREASE EXCHANGE BY• INCREASE FIBROUS
TISSUE IN VILLI• FIBRINOID DEPOSIT ON
SURFACE OF VILLI• OBLITERATION OF SMALL
CAPPILARIES
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Variations of placenta• Normally---hemochorial and eccenteric• Variations• velamentous –when umblical vessels divide before and branches come to
placenta• Marginal- when umblical vessels join placenta at margin• Succenturiate- when additional small plcental lobe is present or separate
small placenta is present• accreta- when placental reaches up to basal layer of endometrium• Increta- when placental infiltrates in the myometrium• Percreta- when placenta infiltrates up to connective tissue and crosses the
muscule layer
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AMNIOTIC FLUID• SYNTHESIZED BY• CLEAR WATERY FLUID • MAINLY BY• MATERNAL CIRCULATION• PARTLY BY AMNIOCYTES• 30-ML—10TH WEEK• 350 ML—20TH WEEK• 800-1000 ML---37TH WEEK• REPLACED /3-4 HRS• 5TH MONTH ONWARD • SWALLOWING• AND ADDITION OF URIN• FUNCTIONS• ABSORBS JOLTS• ALLOW FETAL MOVEMENTS• HORMONE PRODUCTION• AVOIDS ADHERENCE
• Polyhydroamnios• Amount of amniotic fluid• more than 1500 ml eg• Esophageal atresi, anencephaly
• Oligohydroamnios• Amount of amniotic fluid• less than 400 ml eg• Renal agenesis
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Membranes in twins
• DIZYGOTIC OR FRATERNAL twins
• Separate amniotic and chorionic membranes and placenta
• May be different sex, blood groups, features
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Monozygotic twins
• If twins form by the division of zygot at two cell stage with the formation of two separate blastocyst
• Two Separate amniotic and chorionic membranes and placenta
• Features,Sex and blood groups same
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• If twins form by the division of inner cell mass in blastocyst
• Two Separate amniotic cavities
• Common chorionic membranes and placenta
• Features, Sex and blood groups same
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• If twins form by the late division of inner cell mass in blastocyst or by division of bilaminar germ disc
• Common amniotic, chorionic membranes and placenta
• Features, Sex and blood groups same