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Foetal Life Support Systems

While the the blastocyst begins to form distinct layers (cf. implantation ), 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 uterine 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 birth .

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

Other HON resources 
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Embryonic Structures
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Growth and Embryonic Development:

Umbilical Cord
Fetal Blood:

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Growth and Embryonic Development
Umbilical Cord
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