The embryo starts to form major organs (like the heart, liver, stomach, kidney) and systems (circulatory – blood and blood vessels, digestive – gastrointestinal tract, nervous – spinal cord). The embryo measures around .13 – .14 inches—and baby’s gearing up for much more growth.
Your baby is now organized in a C-shape tube with a top, bottom, front, and back. The embryo’s back contains a groove which later becomes the spinal cord. The top of the tube is wider, and flatter top and becomes your baby’s brain. The center of the embryo has a bulge which will become a tiny U-shaped tube forming the heart. The embryo is encased in protective membranes and attached to a yolk sac. The yolk sac manufactures the embryo’s unique blood cells. At this time, the placenta develops. Through the placenta (and its fingerlike projections, called chorionic villi), the embryo receives nourishment from its mother.
The first system to be operational is the circulatory system, or blood — along with the heart. The baby’s heart has two tiny channels called heart tubes.