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The Placenta and the Embryo
Per Brodal
Institutt for medisinske basalfag
Universitetet i Oslo
9th Semester 2008
Week 12
Approx. 6 cm Crown
Rump (CR) length
England 1983
P. Brodal 2008
2
Week 12 (approx.)
Placenta
Fetal
membranes
England 1983
P. Brodal 2008
3
Week 7
Placental villi
Amnion
P. Brodal 2008
England 1983
4
Placenta
Larsen, 3d Edition
P. Brodal 2008
Placental villi
5
The First Week
Day 4:
Morula
Shedding of the
zona pellucida
Day 5:
Blastocyst
Day 6:
Implantation
Fertilization
P. Brodal 2008
6
Implantation – 6th day
Endometrium
Inner cell
mass: gives
rise to the
embryo
Trophoblast start to
invade the
endometrium
Outer cell mass
(trophoblast):
gives rise to the
placenta
Langman, 8 Ed.
P. Brodal 2008
7
Chorion and Decidua
(End of Second Month)
Decidua
parietalis
Decidua
capsularis
Decidua basalis
Chorion
frondosum (villi)
Amniotic cavity
Chorion laeve
Chorion: forms fetal
part of the placenta
Langman, 8 Ed.
P. Brodal 2008
Decidua: forms
maternal part of the
placenta
8
Decidua – Transformed Cells of the
Endometrial Stroma
Decidua parietalis
Decidua capsularis
 large, round, epithelial-like
cells
 secrete nutrients and
regulatory substances
 Important for successful
placentation
P. Brodal 2008
9
7th day
Endometrium
changes: Decidual
reaction
Syncytiotrophoblast
Cytotrophoblast
Amnioblasts
Ectodermal cells
Langman, 8 Ed.
P. Brodal 2008
Entodermal cells
10
9th day: Further Development of the
Placenta
Maternal blood vessels
Lacunae in the
syncytiotrophopblast
Cytotrophoblast
P. Brodal 2008
11
12 days
Maternal sinusoids
connect with
lacunae in the
trophoblast
Primitive
yolk sac
Endometrial
epithelium
Langman, 8 Ed.
P. Brodal 2008
12
13 days
Amniotic cavity
Trophoblastic lacunae
present all around
the embryo
Yolk sac
Extra-embryonal
coelom (chorionic
cavity)
Sometimes a small
bleeding occurs at
this stage
Langman, 8 Ed.
P. Brodal 2008
13
End of Third Week
Cytotrophoblast
Syncytiotrophoblast
The cytotrophoblast
grows through the
syncytiotrophoblast
to form an external
shell
Langman, 8 Ed.
P. Brodal 2008
14
The Cytotrophoblastic Shell (End of 3d
Week)
Cytotrophoblasts
Syncytiotrophoblast
Umbilical cord
Langman, 8 Ed.
P. Brodal 2008
15
Placental Villi – at Fourth Week
and Fourth Month
Maternal blood vessels
Cytotrophoblast
shell
Syncytiotrophoblast
Decidua
(endometrium)
Intervillous
space
(maternal
blood)
Villous blood vessels
(fetal)
P. Brodal 2008
Villus with extra-embryonal
mesoderm
16
Development of the Villi
Primary villus
Secondary villus
Tertiary villus (end of third week)
Diffusion barriere
Langman, 8 Ed.
Early
P. Brodal 2008
Late
17
Foeto-Placental Circulation (End of 4th
Week)
Cardinal veins
(anterior and
posterior)
Dorsal aorta
Umbilical artery (2)
Placental
villi
Vitelline artery
Yolk sac
P. Brodal 2008
Umbilical vein (1)
18
The Placenta at Term
Decidual plate
Amnion
P. Brodal 2008
Decidual septum
Spiral artery
Chorionic plate
Umbilical cord
19
The Placenta at Term
15-25 cm diameter, 500-600 g, 3 cm thick
Exchange area: ~ 10 m2
Blood flow: 600 ml/min
Cotyledon
Amnion
P. Brodal 2008
Umbilical cord
Decidual layer
removed
20
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
P. Brodal 2008
Langman, 8 Ed.
21
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
P. Brodal 2008
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Fetal Membranes
Amnion
(vannhinnen)
P. Brodal 2008
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Fetal membranes – Dizygotic twins
2 cell zygote
Fused chorions
Langman
P. Brodal 2008
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Fetal membranes - Monozygotic Twins
2-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
P. Brodal 2008
25
Formation of The Umbilical Cord
Amnion
Yolk sac
P. Brodal 2008
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Bilaminar germ disk (2d week)
Amnion
Ectoderm
Entoderm
Langman, 8 Ed.
P. Brodal 2008
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Formation of the Mesoderm
(2d-3d Week)
Ectoderm
Entoderm
Mesoderm
Week 3
Langman, 8 Ed.
P. Brodal 2008
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Third week – Trilaminated Disc
Amniotic cavity
Amnion
Ectoderm
Intra-embryonic
coelom (starting
to form)
Mesoderm
(paraxial)
Entoderm
Langman
P. Brodal 2008
Yolk sac
29
Foldings Determine the Shape of the
Embryo (Fourth week)
Neural tube
Amniotic cavity
Intermediate
mesoderm
(nephrotomes)
Paraxial mesoderm
(somit)
Intraembryonic
coelom
Midgut
Yolk sac
P.Langman
Brodal 2008
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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
P. Brodal 2008
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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.
P. Brodal 2008
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