By pregnancy week 3, the structuring of the embryo will begin to take shape. The inner layer of the blastocyst, known as the embryoblast will have separated into 3 separate 'germ layers', with each layer having it's distinctive encoding for the growth of assorted parts of the embryo's organs. This embryonic stage is known as Organogenesis. Organogenesis defines the condensing, splitting and folding of the layers into different organ forms.
Two vital developments in this initial stage are:
The Notochord - This lithe rod appears through the main part of the embryo and defines it's fundamental axis from which everything else will take shape around. After the folds close it will be replaced by the spinal column. The Notochord, at this stage, acts as a primal 'control center' commanding instructional augmentation and functional process to everything around it prior to the evolution of the brain and nervous system. It achieves this by secreting growth proteins that program surrounding tissues of the germ layers to undergo differentiated developments. The essential organs of the embryo would be incapable of forming without it.
The neural tube is an another vital development when you are 3 weeks pregnant. This tube is the precursor to the central nervous system which includes the spinal cord and the brain and wraps itself round the Notochord. A lengthy, narrow, cylinder tube, extending from the brain, is all that houses the bundle of raw nerves that is the spinal cord. 'Somites' are cell formations, situated on either side of the neural tube, that will later grow into the skeletal muscle, spinal nerves and vertebrae (spinal bones).
The hollow chamber that will soon develop into the heart will also take shape by the end of this week. With all this chief groundwork that takes place, it's almost inconceivable when you come to realize that the embryo is still only the size of a pinhead.
To find out more about the developments of pregnancy week 3, or to follow your stages of pregnancy development week by week, you can visit us at: http://www.stages-of-pregnancy-development.com
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