3[1].palcenta fetal membrane

Fetal Membranes, Placenta and Twinning

OBJECTIVES

1. The components of fetal membrane and their functions.

2. Structure and function of placenta

3. Composition of Placenta barrier

Fetal membrane — overview

•Originate from blastocyst, don’t participate in the formation of embryo

•Including:

1) Chorion

2) Amnion

3) Yolk sac

4) Allantois

5)Umbilical cord

Chorion•Formed by

trophoblast +extraembryonic mesoderm

Chorion• Primary villi: cytotrophoblast+syncytiotrophoblast

• Secondary villi: extraembryonic mesoderm enter the

primary villi

• Tertiary villi: extraembryonic mesoderm =>CT+BV

Chorion frondosum-embryonic pole Chorion laeve-abembryonic pole

Function of Chorion1) Exchange of metabolite:

portion of placenta (Chorion frondosum)

2) Hormone production:

human chorionic gonadotropin (HCG)

Amnion•Amniotic membrane: amniotic epi.+ extraembryonic mesoderm

•Amniotic 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

Amnion - Fluid• Functions

– Mechanically cushion – Protect from fetus adhesion– Movement– Maintain Temp

• Abnormalities1) too much (polyhydramnios) >2000 ml Abnormal digestive system

or CNS - esophageal atresia - anencephaly2) too little (oligohydramnios) <500 ml Abnormal urinary system - poor development of

kidney - urethra atresia

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

Umbilical Cord

• Folding – a purse string closure– Amnion membrane

covered– Cord: mucous CT, 3

vessels,yolk sac ,allantois

– 50-60 cm, 2cm diameter

– Long – knots– Short – abruption

Placenta - Overview• Functions as:

– Lungs, GI tract, Liver, Kidneys, Endocrine

• Placenta proper: Chorion frondosum+ Decidua basalis

Anatomy of the Placenta

• Fetal – Chorion– Chorion Frondosum– Chorion Laeva

• Maternal – Decidua– Decidua Basalis– Decidua Capsularis– Decidua Parietalis

Anatomy of the Placenta

• At birth 500 g• 15-25 cm Diameter• 3 cm thick• Anchoring villi• Decidual septa

15-20 Cotelydons

Placental-Fetal Circulation• Fetus: umbilical A carries O2/nutrient depleted blood

to cap. of chorion , exchange with maternal blood of the intervillous spaceumbilical V

• Mother: spiral A intervillous space uterine V

Placental Barrier

--the structure between fetal and maternal blood

--components:

1)endothelium of chorion capillary

2) CT in the core of the villus

3) trophoblast epithelium

Placental Function1.Exchange of Metabolites:

nutrients antibody, waste 2.Defense barrier3.hormone production- human chorionic gonadotropin (HCG) Begin: end of 2nd week Highest: 2nd month- Estrogen and progesterone- Placental lactogen

Twins

Two types: – One zygote

(monozygotic)– Two (or more) zygotes

(dizygotic)• 2 (or more) oocytes• Non Identical

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