Biology Forums - Study Force

I'm having some difficulty understanding the three germ layers.

I always read that certain germ layers are the origin of certain organs, but I'm having trouble accepting this. For example, the liver and pancreas are both derived from the endoderm, but they clearly have blood vessels, which are of mesoderm origin. What about muscles and other enervated organs? Aren't nerves from the ectoderm, but it's common to say muscles are of mesoderm origin.

I also find it super confusing that some cells/tissue types are only from one germline (i.e. muscle, blood, etc. are from mesoderm or neurons are from ectoderm) while others seem to be derived from more than one (epithelial cells can come from either the ectoderm or endoderm!)

I'm clearly confused here  :sweat:

You just have to keep in mind that ectoderm is the outermost layer, endoderm the innermost layer, and mesoderm the layer in between.  If you keep this concept in mind, you should be a little less confused :)