subject: Pregnancy Week 3 - How The Embryo Grows [print this page] Author: Julie Watkins Author: Julie Watkins
During pregnancy week 3, the early formation of the embryo will begin. Each vital organ will be individually shaped from the 3 seperate 'germ layers' of the embryoblast (which is the 'yolk' part of the blastocyst). This embryonic phase is known as Organogenesis which is the splitting, folding and condensing of the organs. Predominantly, 2 vital developments will arise: The Notochord - This appears through the main part of the embryo as a lithe rod from which all further organs will be structured around. When the folds seal it will be replaced by the spinal column. Prior to the brain and nervous system growing, the Notochord will act as a primitive 'control center' to lead and instruct the development and function of a range of vital organs. Neighboring germ layers will get instructional commands from the Notochord in the form of secreted growth proteins. The spinal cord, muscles and organs would be unable to develop without this direction. The Neural Tube is another essential development when you are 3 weeks pregnant. This tube is the precursor to the nervous system which includes the brain and spinal cord. The spinal cord extends from the brain and contains a bunch of raw nerves that is enclosed inside a long, thin, hollow tube. 'Somites' are cell formations, on each side of the neural tube, that will soon develop into the skeletal muscle, spinal nerves and vertebrae (spinal bones). The heart will also develop by the end of this week in the form of a hollow chamber. It's astonishing to know that all of this growth takes place inside an embryo that is stil no larger than the size of a pinhead.About the Author:
