Download Embryonic Adaptations

EXTRAEMBRYONIC
ADAPTATIONS
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Extraembryonic - structures that assist
embryonic development, but that in most cases
(there is one exception) don’t form functional
structures in the juvenile or adult.
Extraembryonic structures are generally left
behind at hatching or birth, or they are
reabsorbed shortly thereafter.
Extraembryonic structures may be acellular or
cellular.
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Acellular extraembryonic
structures associated with
the egg/zygote:
Secondary oocyte of hampster from which the
cumulus cells have been removed by treatment
with hyaluronidase.
http://www.mybitoftheplanet.com/2004/big_pictures/mar/spawn0503.html
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Acellular extraembryonic
structures associated with
the avian egg/zygote:
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Cellular extra-embryonic structures.
Extraembryonic structures are more
complex in higher vertebrates amniotes (reptiles, birds, mammals)
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Purposes of extraembryonic structures:
Acellular extraembryonic structures (vitelline/fertilization membrane, zona pellucida, jelly
layers, albumin, shell, shell membranes)
1.
Aid in preventing polyspermy
2.
Create an axenic (bacteria free) environment for
development.
3.
May deter predation
4.
Protect from mechanical damage
5.
Prevent dehydration (birds, reptiles)
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Purposes of extraembryonic structures:
Cellular extraembryonic structures (amnion, chorion, yolk sac, allantois)
1.
Actively participate in gaseous transport (oxygen,
CO2) to and from embryo. (chorion, allantois)
2.
Actively participate in transport of nutrients to
embryo. (birds & reptiles- yolk sac, mammals chorion, allantois [sometimes (e.g. pig embryos) the
yolk sac during early development])
3.
Actively participate in storage or transport of
metabolic waste. (birds & reptiles - allantois,
mammals - chorion, allantois)
4.
Source of primordial germ cells (yolk sac mesoderm)
5.
Source of early blood stem cells (yolk sac
extraembryonic splanchnic mesoderm)
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Origin of the somatopleure and splanchnopleure
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Amnion - extraembryonic ectoderm + extraembryonic somatic mesoderm =
......................................................................extraembryonic somatopleure
Chorion - extraembryonic ectoderm + extraembryonic somatic mesoderm =
......................................................................extraembryonic somatopleure
Yolk sac - extraembryonic endoderm + extraembryonic splanchnic mesoderm =
....................................................................extraembryonic splanchnopleure
Allanois -extraembryonic endoderm + extraembryonic splanchnic mesoderm =
....................................................................extraembryonic splanchnopleure
Germ layer origin of the cellular
extraembryonic membranes of
amniotes.
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Effect of increasing yolk volume on development
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Formation of extraembryonic membranes in chickens (amniotes)
The head fold
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Seroamniotic folds
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sagittal
sagittalsection
section
transverse section
transverse section
38
38hr
hrchicken
chickenembryo
embryo
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48-55 hr chicken embryo, sagittal view
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1
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The Allantois
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Allantois
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sagittal section
sagittal section
transverse section
transverse section
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chicken
embryo
72 hr
hr chicken
embryo
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