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Conception & The Germinal Period of Development

Conception refers to the fertilisation of the female egg or ovum by the male sperm. During a woman's menstrual cycle , one ovum per month is released between day 9 and 16 of an idealised 28 day cycle, a process termed ovulation . When an ovum is released from one of the two ovaries, it makes its way to the uterus, via the fallopian tubes . It is here, in one of the fallopian tubes that fertilisation occurs, provided that sperm are present and manage to successfully enter the ovum.

Following the fertilisation of the ovum, prenatal development is divided into 3 main periods:
Germinal
, Embryonic and Foetal .

The Germinal Period is the first 2 weeks post- conception , where the fertilised ovum, now termed a zygote , is created and attaches to the uterine wall.

Following fertilisation, the zygote begins to divide rapidly as it moves into the uterus from the fallopian tube. By the time the zygote has arrived in the uterus, 4 to 5 days post-fertilisation, it is a hollow mass of 64-128 cells. Cell differentiation of the zygote has already begun: between the inner layer of cells or blastocyst and the outer layer or trophoblast . It is the trophoblast, which then attaches itself to the uterus wall in a process called implantation and goes on to become the various life support systems (placenta, amniotic sac, umbilical cord), while the blastocyst develops into the embryo .

On rare occasions two eggs ( ova ) may be released and fertilised, resulting in fraternal twins , or the single fertilised ovum may initially divide into two separate cells, which continue to develop independently, resulting in identical twins .

If fertilisation does not occur, the egg exits the body with the next menstrual period .

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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Fertilization
Zygote:
(www.advancedfertility.com)
Advanced Fertility Center of Chicago

Blastocyst:
(www.advancedfertility.com)
Advanced Fertility Center of Chicago

Trophoblast

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  http://www.hon.ch/Dossier/MotherChild/pregnancy/conception.html Last modified: Jun 25 2002