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Foetal Life Support Systems
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While the the
begins to form distinct layers (cf. ),
so too do the life-support systems for the developing embryo, from the
outer layer of this cell mass. These life-support systems include the
amnion/chorion , umbilical
cord and the placenta .
1. The blastocyst wall becomes
the outer layer of membranes or chorion , which
surround the embryo, while another inner layer of membranes becomes the
amnion. These membrane layers develop by the 10th to 12th day post-conception.
The amnion layer forms the amniotic sac , which
fills with amniotic fluid (mostly foetal urine) to provide the embryo
with a shockproof, temperature and humidity controlled inner environment.
2. The umbilical
cord consists of 2 arteries and 1 vein, which provides for the
transport of blood to and from the embryo and placenta.
3. The placenta is where
the mother and embryos' blood vessels intertwine but do not join, to facilitate
the exchange of oxygen, nutrients, and waste materials between the mother
and embryo/foetus. In the placenta, embryonic/foetal blood flows into
thousands of tiny projections ( villi ), where exchanges occur between
the mother and embryo/foetus. The placenta covers about a quarter of the
surface, thus
providing a large surface area for such exchange. By the 18th to 20th
week of pregnancy, the placenta is fully formed, and is about 450gms (1lb)
by .
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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