Medical visualization taken from human scanned data showing heart and brain development from the embryonic period at week 6 to the fetal period at week 16. From left to right, this composited image shows each stage of organ development from weeks 6-10 as well as week 16. At week 6 a heart tube has developed from mesodermal tissues, and the final stage of heart development is formed at week 10, meaning that the heart has two atria, two ventricles, and the blood vessels necessary for circulation. The nervous system is formed from a structure called the neural tube, which begins to form around the 25th day after conception. Once the neural tube closes, the more specific regions and structures in the brain begin to form and fall into place. Neural circuits, or connections between neurons that communicate information throughout the brain, are formed in the fetal period. |