FETAL MEMBRANES AND PLACENTABY

PROF MASOOD AHMEDMBBS, MPHIL PHD

Relative Size of Human Conceptus

Implantation of the Blastocyst

Implantation of the Blastocyst

FETAL MEMBRANES

REFRESH FEW TERMSDECIDUA BASALIS, CAPULARIS

AND PARIETALISVILLI FORMATIONCYTOTRPHOBLASTIC SHELL

FORMATIONCHORIONIC MEMBRANE

PARTSCHORION FURONDOSUM AND

CHORION LAEVEAMNIOCHORIONIC

MEMBRANE

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

CYTOTROPHOBLASTIC SHELL FORMATIONPLACENTAL BARRIER/ MEMBRANE

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

AMNION WITHIN CHORION

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

• UTERO PLACENTAL CIRCULATION –12TH DAY CIRCULATION

• 4TH MONTHCHORION FRONDOSUM AND DECIDUA BASALIS• 5TH MONTHDECIDUAL SEPTA AND COTYLEDON FORMATIONCONTIOUS FLOW IN INTERVILLOUS SPACE

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

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

Placentation

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

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

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

Membranes in twins

• DIZYGOTIC OR FRATERNAL twins

• Separate amniotic and chorionic membranes and placenta

• May be different sex, blood groups, features

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

• 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

• 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