FETAL MEMBRANES AND PLACENTA BY PROF MASOOD AHMED MBBS, MPHIL PHD

Relative Size of Human Conceptus

Implantation of the Blastocyst

Implantation of the Blastocyst

FETAL MEMBRANES REFRESH FEW TERMS DECIDUA BASALIS, CAPULARIS AND PARIETALIS VILLI FORMATION CYTOTRPHOBLASTIC SHELL FORMATION CHORIONIC MEMBRANE PARTS CHORION FURONDOSUM AND CHORION LAEVE AMNIOCHORIONIC 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 FORMATION PLACENTAL 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 MONTH CHORION FRONDOSUM AND DECIDUA BASALIS 5TH MONTH DECIDUAL SEPTA AND COTYLEDON FORMATION CONTIOUS FLOW IN INTERVILLOUS SPACE

PLACENTAL SURFACES Functional type hemochorial 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 DECREASE EXCHANGE BY INCREASE FIBROUS TISSUE IN VILLI 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 Polyhydroamnios Oligohydroamnios 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 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