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Fetal Membranes, Placenta andTwinning

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OBJECTIVES

1. The components of fetal membrane and their

functions.2. Structure and function of placenta

3. Composition of Placenta barrier

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Fetal membrane overview

Originate from blastocyst, dontparticipate in the formation ofembryo

Including:

1) Chorion

2) Amnion

3) Yolk sac

4) Allantois

5)Umbilical cord

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ChorionFormed by

trophoblast +extraembryonic mesoderm

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Chorion

Primary villi: cytotrophoblast+syncytiotrophoblast

Secondary villi: extraembryonic mesoderm enter the

primary villi

Tertiary villi: extraembryonic mesoderm =>CT+BV

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Chorion frondosum-embryonic pole

Chorion laeve-abembryonic pole

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Function of Chorion

1) Exchange of metabolite:

portion of placenta (Chorion frondosum)

2) Hormone production:

human chorionic gonadotropin (HCG)

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Amnion

Amniotic membrane: amniotic epi.+ extraembryonic mesodermAmniotic fluid:

Produce:1)amniotic cells

2) infusion of fluid from maternal blood

3) urine output from the fetus

4) pulmonary secretions

Output: 1) absorbed by amniotic cells

2) fetus swallow

1 liter circulate

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Amnion - Fluid Functions

Mechanically cushion

Protect from fetus adhesion

Movement

Maintain Temp

Abnormalities1) too much (polyhydramnios)

>2000 ml

Abnormal digestive system orCNS

- esophageal atresia

- anencephaly

2) too little (oligohydramnios)

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Yolk sac and Allantois

Yolk sac Primitive Gut

3rd week, Germ Cells

3rd to 6th week,

Blood island

Allantois Caudal extension of

hindgut

Allantoic A pairs

Allantoic V pairs

Umbilical vessels

2A+1V

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Umbilical Cord

Folding a purse stringclosure

Amnion membrane

covered Cord: mucous CT, 3

vessels,yolk sac ,allantois

50-60 cm, 2cm diameter

Long knots

Short abruption

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Placenta - Overview Functions as:

Lungs, GI tract, Liver, Kidneys, Endocrine

Placenta proper:

Chorion frondosum+ Decidua basalis

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Anatomy of the Placenta

Fetal Chorion

Chorion Frondosum

Chorion Laeva Maternal Decidua

Decidua Basalis

Decidua Capsularis

Decidua Parietalis

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Anatomy of the Placenta

At birth 500 g

15-25 cm Diameter

3 cm thick

Anchoring villi

Decidual septa 15-20 Cotelydons

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Placental-Fetal Circulation Fetus:

umbilical A carries O2/nutrient depleted blood to cap.of chorion , exchange with maternal blood of theintervillous spaceumbilical V

Mother:

spiral A intervillous space uterine V

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Placental Barrier

--the structure between fetal and maternal blood

--components:

1)endothelium of chorion capillary

2) CT in the core of the villus3) trophoblast epithelium

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Placental Function

1.Exchange of Metabolites: nutrientsantibody, waste

2.Defense barrier

3.hormone production

- human chorionic gonadotropin (HCG)Begin: end of 2nd week

Highest: 2nd month

- Estrogen and progesterone

- Placental lactogen

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Twins

Two types:

One zygote (monozygotic)

Two (or more) zygotes(dizygotic)

2 (or more) oocytes

Non Identical

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Twins

- Monozygotic Zygote split

2-4 cell

2 amn, 2 chorion Blastocyst

2 amn, 1 chorion

Bilaminar germ disc

1 amn, 1 chorion Incomplete splitting

Conjoined twins