The Placenta and the Embryo The Placenta and the Embryo

Per BrodalPer BrodalInstitutt for medisinske basalfagInstitutt for medisinske basalfag

Universitetet i OsloUniversitetet i Oslo

9th Semester 20089th Semester 2008

Week 12

England 19832

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Approx. 6 cm Crown Rump (CR) length

Week 12 (approx.)

Placenta

Fetal membranes

England 19833P. Brodal 2008

Week 7

England 1983

Placental villi

Amnion

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Placenta

Larsen, 3d Edition Placental villi5

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The First Week

Day 5: Blastocyst

Day 6: Implantation

Day 4: Morula

Shedding of the zona pellucida

Fertilization6P. Brodal 2008

Implantation – 6th day

Endometrium

Inner cell mass: gives rise to the embryo Outer cell mass

(trophoblast): gives rise to the placenta

Trophoblast start to invade the endometrium

7P. Brodal 2008

Langman, 8 Ed.

Chorion and Decidua (End of Second Month)

Decidua basalis

Chorion frondosum (villi)

Chorion laeve

Decidua capsularis

Decidua parietalis

Amniotic cavity

Chorion: forms fetal part of the placenta

Decidua: forms maternal part of the placenta

Chorion: forms fetal part of the placenta

Decidua: forms maternal part of the placentaLangman, 8 Ed.

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Decidua – Transformed Cells of the Endometrial Stroma

Decidua capsularisDecidua parietalis

large, round, epithelial-like cells

secrete nutrients and regulatory substances

Important for successful placentation

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7th day

Endometrium changes: Decidual reaction

Syncytiotrophoblast

Cytotrophoblast

Amnioblasts

Ectodermal cells

Entodermal cells

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Langman, 8 Ed.

9th day: Further Development of the Placenta

Cytotrophoblast

Lacunae in the syncytiotrophopblast

Maternal blood vessels

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12 days

Primitive yolk sac

Maternal sinusoids connect with lacunae in the trophoblast

Endometrial epithelium

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Langman, 8 Ed.

13 days

Trophoblastic lacunae present all around the embryo Extra-embryonal

coelom (chorionic cavity)

Amniotic cavity

Yolk sac

Sometimes a small bleeding occurs at this stage

Sometimes a small bleeding occurs at this stage

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Langman, 8 Ed.

End of Third WeekCytotrophoblast

Syncytiotrophoblast

The cytotrophoblast grows through the syncytiotrophoblast to form an external shell

The cytotrophoblast grows through the syncytiotrophoblast to form an external shell

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Langman, 8 Ed.

The Cytotrophoblastic Shell (End of 3d Week)

Umbilical cord

Cytotrophoblasts

Syncytiotrophoblast

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Langman, 8 Ed.

Placental Villi – at Fourth Week and Fourth Month

Cytotrophoblast shell

Syncytiotrophoblast

Villus with extra-embryonal mesoderm

Maternal blood vessels

Decidua (endometrium)

Villous blood vessels (fetal)

Intervillous space (maternal blood)

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Development of the Villi

Primary villus Secondary villus Tertiary villus (end of third week)

Diffusion barriere

Early Late 17P. Brodal 2008

Langman, 8 Ed.

Foeto-Placental Circulation (End of 4th Week)

Umbilical artery (2)

Umbilical vein (1)

Dorsal aortaCardinal veins (anterior and posterior)

Yolk sac

Vitelline arteryPlacental villi

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The Placenta at Term

Chorionic plate

Decidual plate Spiral artery

Umbilical cordAmnion

Decidual septum

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The Placenta at Term15-25 cm diameter, 500-600 g, 3 cm thick

Exchange area: ~ 10 m2

Blood flow: 600 ml/min

15-25 cm diameter, 500-600 g, 3 cm thick

Exchange area: ~ 10 m2

Blood flow: 600 ml/min

Amnion Umbilical cordCotyledon

Decidual layer removed

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Extravillous Trophoblast

Trophoblastic cells growing as columns into the decidua, forming anchoring villi

Invading also the uterine arteries – eroding the media and forming the intima

Important for maintaining perfusion of the placenta

Inadequate formation: related to preeclampsia

Ecxessive: invasive growth, e.g. choriocarcinoma

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Langman, 8 Ed.

The Fetal Membranes (End of 4th Month)

Fusion of amnion, chorion laeve, decidua capsularis and decidua parietalis

Fusion of amnion, chorion laeve and decidua capsularis

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Fetal Membranes

Amnion (vannhinnen)

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Fetal membranes – Dizygotic twins

2 cell - zygote

Fused chorions

Langman

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Fetal membranes - Monozygotic Twins2-cell zygote

Split at 2-cell stage; separate chorion and amnion

Split of inner cell mass early; share chorion, separate amnion

Split of inner cell mass late; share chorion and amnion

Langman

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Formation of The Umbilical Cord

AmnionYolk sac

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Bilaminar germ disk (2d week)

Amnion

Entoderm

Ectoderm

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Langman, 8 Ed.

Formation of the Mesoderm (2d-3d Week)

Week 3

Ectoderm

Entoderm Mesoderm

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Langman, 8 Ed.

Third week – Trilaminated Disc

Langman

AmnionAmniotic cavity

Yolk sac

Entoderm

Ectoderm

Mesoderm (paraxial)

Intra-embryonic coelom (starting to form)

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Foldings Determine the Shape of the Embryo (Fourth week)

Langman

Intraembryonic coelom

Midgut

Yolk sac

Amniotic cavity Paraxial mesoderm (somit)

Intermediate mesoderm (nephrotomes)

Neural tube

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Some Landmarks in Embryonic Development

2d-3d week: The trilaminar germ disc formed 3d week: The heart develops, links up with

the vascular system 4th week: Formation of the gut 6th week: Urogenital sinus formed 7th week: most organs have formed

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Some Landmarks in Fetal Development (weeks after fertilization)

6 weeks ~ 2 cm CR-length; nose, ears, fingers identifiable

10 weeks ~ 6 cm; external genitals formed but undifferentiated

14 weeks ~ 12 cm; external genitals can be differentiated, skin transparent red

18 weeks ~ 15 cm; fine hairs (lanugo) covers the body, skin opaque

22 weeks ~ 21 cm; eyebrows and fingernails present 26 weeks ~ 26 cm; eyes open, scalp hair growing

Llewellyn-Jones 7th Ed.32P. Brodal 2008