endoderm

endoderm The innermost of the three primary germ cell layers (the other two being the mesoderm and ectoderm) that make up the very early embryo. It differentiates to give rise first to the embryonic gut and then to the linings of the respiratory and digestive tracts and the liver and pancreas. Also referred to as entoderm. See also differentiation; ectoderm; embryo; mesoderm.