Describe the key changes that take place in the growing embryo up to eight weeks.

Many key changes happen to the growing embryo during the first eight weeks.The embryo begins as a mass of cells. During a period of approximately five weeks, it develops the basic physical features of a human being as well as the internal organs which will combine to create its body systems. This period also includes the creation of the neural tube. The neural tube lays the groundwork for the development of the human brain.

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The embryonic stage of prenatal development begins about three weeks after conception and lasts until the eighth week, when the fetal stage begins. During this stage, the embryo- the mass of cells generated during the gestation period- begins to take on rudimentary human characteristics.

One of the most crucial early developments in the embryonic stage is the formation of the neural tube, a hollow tube arising out of the neural plate which will form the basis for the central nervous system and the brain. The neural tube allows for the distribution of neurons to different areas of the brain, where they connect with each other to create the neural networks that humans depend on for the rest of their lives.

During this period, the embryo also expands into the physical features that define human beings. The head is formed around the fourth week, followed by facial features such as the eyes, ears, and mouth. The next week brings the emergence of four small buds that will grow into the arms and legs. By eight weeks, these buds have expanded to the point that the arms have elbows and the legs have knees. The embryonic stage also includes the growth of the major human organs which form the building blocks for the cardiovascular, respiratory, digestive, and circulatory systems.

By the eighth week, when the embryo enters the fetal stage, it possesses the fundamental physical characteristics of a human being along with the internal organs needed to form its signature body systems.

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