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The Embryonic Period

by — Last updated: 2014-05-08 in Pregnancy

Table of Contents

Ever wondered how a baby grows and develops inside the womb? It is not a simple process, but is quite amazing. Here is a description of how a baby develops, from the moment of conception, passing through its organs and body formation until its birth.

It has been two weeks after fertilization now and the blastocyst is fully implanted on the uterine wall. The embryonic period starts and the formation of the baby’s organs too.  The embryo is still very tiny at this stage, almost as tiny as the tip of a pen.

From cells to a fully formed tiny human

The embryo is formed by three layers of cells, which will give rise to different organs, depending on their localization.

The ectoderm is the outermost layer and it gives rise to the nervous system, the ears, nose and eyes, the skin, hair, nails and teeth, and the pituitary and mammary glands. The mesoderm is made of the cells located in the middle of the embryo. From these the baby’s bones, kidneys, heart and reproductive system will form. Finally, the inner cell layer, also known as endoderm is the one from which the gastrointestinal, respiratory and urinary systems derive, as well as the thyroid and parathyroid glands, the thymus, the pancreas and the liver.

Before week three ends, the central nervous system starts developing, followed by the spinal cord and every other system that will form the embryo’s body. When week four starts, the heart of the embryo is already pumping blood.

Cardiovascular system in general is the first system to start functioning in a baby.

At the same time, the musculoskeletal, digestive, respiratory, urogenital and the rest of the nervous system, as well as the sense organs, begin to develop. Also, the head and neck start forming, giving the embryo its particular C-shaped appearance. As time goes by, facial features and extremities will derive from their correspondent embryonic structures.

Five weeks after conception you can already identify the embryo’s tiny nostrils and in week 8, it’s eyes and nose are already visible, as well as the structures that will form its arms, legs, fingers and toes.

The final countdown

The embryonic period ends by the 8th week, after which the new being is called fetus.

From this time on, the fetus will start growing rapidly and its tissues will mature during this stage.

See Also: IVF And Twins: Stronger Embryo Helps A Weaker One Survive

Would you like to know if it is a boy or a girl? At the 9th week after conception, the fetus genitals will start to develop according to the information carried in the Y chromosome. So, basically the information provided by the father is the one that determines the sex of the baby and you will be able know if it's a boy or a girl by the third month.

There are still 6 more months to go. During this time, the fetus continues its growth and starts moving. By the ninth month, it reaches a size of approx.. 40 cm. and weighs from 6 to 8 pounds. It is ready now to come into the outer world.