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Parents might wonder if vampire myths
originate in an unconscious recollection of
this earliest mother-child encounter.
Barry Werth, 2002
Placentation
This section will explore the intimate relationship formed between the
developing embryo and the mother. From its initial contact with the uterine
wall the developing embryo becomes an endoparasite that takes advantage
and maintains its own well-being at the expense of mom. Not only does
the embryo tap into mom’s blood supply, but it also influences her entire
hormonal regime. After this lecture you should be able to:
• Describe the process of implantation.
• Describe the extraembryonic membranes and their associated
structures and the structure of the placenta.
• Describe the fetal contribution to the placenta.
• Describe the maternal contribution to the placenta.
• Explain the process of the circulatory exchange within the placenta
and the relation to the blood flow in the mother and the fetus.
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Anatomy of the Uterine Wall
The mammalian nest
Three-layered structure
Perimetrium – serosa
Myometrium – smooth muscle coat
Endometrium – mucosa
Endometrial stroma
Endometrial epithelium
Functional divisions of endometrium
Stratum functionalis or decidua
Stratum basalis
Implantation
Endoparasitic invasion of the uterine wall
Uterine contact
When
Where
How
E m b r y o l o g y
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L e c t u r e
M a n u a l
b y
M a r k
N i e l s e n
P l a c e n t a t i o n
Differentiation and development of the trophoblast
Cytotrophoblast
Syncytiotrophoblast
Rapid hypertrophy
Timeline
8 days
Enzymatic erosion of uterine wall
Emergence of lacunae
9 days
Disruption of endometrial vessels and glands
Formation of lacunar network
10 days
Endocrine activity - production of hCG
Completion of implantation
Closing plug – day 10
Complete regeneration of endometrial epithelium – day 12
12 days
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Development of the Chorionic Sac
Limiting membrane of the embryo
Primary chorionic villi
What are they?
Developmental induction
Timeline
Extraembryonic somatic mesoderm
Chorion
Contributions
Chorionic cavity
14 days
Contents of chorionic cavity
Amnionic sac over epiblast
Yolk sac over hypoblast
Connecting stalk
E m b r y o l o g y
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L e c t u r e
M a n u a l
b y
M a r k
N i e l s e n
P l a c e n t a t i o n
Allantois
Development
When does it appear?
From what does it arise?
Comparative embryology
Functional significance
Placenta
Fetomaternal transport system
Fetomaternal organ
Fetal contribution
Maternal contribution
Decidua
Decidua basalis
Decidua capsularis
Decidua parietalis
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Placental development
Development of the chorion
Chorion and decidua basalis
Formation of the villous chorion or chorion frondosum
Chorion and decidua capsularis
Formation of the smooth chorion or chorion laeve
Expansion of villous chorion into decidua basalis
Formation of the intervillous space
Lacunae
Lacunar network
Connection with maternal vessels
Contents of intervillous space
E m b r y o l o g y
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L e c t u r e
M a n u a l
b y
M a r k
N i e l s e n
P l a c e n t a t i o n
Formation of chorionic villi
Primary stem villus
Secondary stem villus
Tertiary stem villus
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Anatomy of the fully developed placenta
Maternal components
Endometrial septa
Maternal blood in intervillous space
Endometrial arteries (spiral) and veins
Fetal components
Chorionic plate
Cytotrophoblastic shell
Cotyledons
Intervillous space
Tertiary stem villus with branching chorionic villi
Fetal capillaries
E m b r y o l o g y
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L e c t u r e
M a n u a l
b y
M a r k
N i e l s e n
P l a c e n t a t i o n
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Placental membrane
Early placenta
Syncytiotrophoblast
Cytotrophoblast
Connective tissue core
Capillary endothelium
Late placenta
Fibrinoid material
Connective tissue
Capillary endothelium
Placental functions
Metabolism
Transport
Endocrine secretion
E m b r y o l o g y
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L e c t u r e
M a n u a l
b y
M a r k
N i e l s e n