Tiny embryo
Deep in your uterus an embryo is growing at a furious pace, and it looks more like a tadpole than a human. The embryo is made up of three layers – the ectoderm, the mesoderm, and the endoderm – which will later form all of the organs and tissues.
Brain development
Your baby’s brain, spinal cord, and nerves form from the neural tube, which is starting to develop from the embryo’s top layer – the ectoderm. This layer will also give rise to skin, hair, nails, mammary and sweat glands, and tooth enamel.
Heart development
The heart and circulatory system begin to form in the embryo’s middle layer, or mesoderm. The mesoderm will also form your baby’s muscles, cartilage, bone, and the tissue under the skin.
Lungs and gut
The third layer, or endoderm, will become the lungs, intestines, and early urinary system, as well as the thyroid, liver, and pancreas. In the meantime, the primitive placenta and umbilical cord, which deliver nourishment and oxygen to your baby, are already on the job.
