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Implantation &The Embryonic Period of Development
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Implantation refers to the
attachment of the
to the wall of the .
The zygote generally implants at the top of the uterus, near where it
exits the , beginning between 5 and 8 days after
and is completed by 9 or 10 days post- .
The outer layer of this cell mass or ,
attaches itself by secreting proteolytic enzymes, which erode the uterine
wall cells, gradually embedding itself firmly in the uterine wall. However,
in certain cases the fertilised egg may develop outside the uterus (cf.
).
We have now entered the embryonic
period of development (2 to 8 weeks post-conception), where the
zygote is now referred to as the embryo .
As the zygote implants and becomes the embryo, the
begins to form 2 layers:
- The inner layer of cells is called the endoderm
and eventually develops into the digestive and respiratory systems.
- The outer layer is divided into 2 parts: the ectoderm
(outermost layer of cells) and mesoderm
(middle layer; between the endoderm and ectoderm). The ectoderm will
develop into the nervous system, sensory receptors (eyes, ears, nose,
etc.) and skin (including nails and hair), while the mesoderm will
become the bones, muscles, excretory, circulatory and reproductive
systems.
While these layers of the embryo form, so too do the
for the developing
embryo, from the outer layer of the cell mass.
The next stage of development, from month 2 until ,
is the .
The information in this page is presented in summarised form and has been taken
from the following source(s):
1.
Child Development , 6th Edition (1994), J. W. Santrock, Wm. C. Brown
Communications, Inc.
2.
Introduction to Human Physiology , 2nd Edition (1981), M. Griffins, Macmillan Publishing
Co. Inc, New York
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 From
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(webvision.med.utah.edu)
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