Sorry, really dull I know, but your pregnancy calendar, weeks 6,7 and 8 reads the following:
Your baby starts off as a flat disc of cells and not, as you might imagine, a cute jellybean. These cells divide continuously and form three layers. These are called the <strong>ectoderm, mesoderm and endoderm.</strong>
This may be more information than you need but what your baby does with these layers is deeply impressive. She somehow manages to grow specific parts of her body from each layer. Each layer is programmed to do its job. You won't get any cells from the <strong>endoderm</strong> layer growing up to be part of your baby's bladder because they develop into the brain, nervous system, hair, nails, enamel in teeth, sweat glands and the linings of the ear, nose, throat and eye.
Do any of these things have anything in common? The answer is yes: they are all parts of the body that come into contact with the outside world in some way - seeing, making sense of it, feeling it and, in the case of teeth, eating it.
The <strong>mesoderm</strong> layer develops into your baby's head and its muscles, bone, heart, arteries, veins and kidneys. It is the layer that supports the body. While the <strong>endoderm</strong> develops into the lining of the body, such as the cells lining the gut, lungs and bladder.
As you can see, the word endoderm is mentioned twice and ectoderm not at all. The ectoderm is the layer concerned with brain, nervous system, hair, nails etc.
Sorry for being such a bore, but I thought you'd like to be as accurate as poss.