What Is the Endoderm?
The endoderm, or entoderm, is one of the three embryonic germ layers that together give rise to all the mature tissues and organs of the body. From the inside out, the three cell layers are the endoderm, the mesoderm, and the ectoderm. The cell layers arise early in embryonic development, when a cavity called the archenteron forms in the center of the blastula, a tiny ball of undifferentiated cells, and the cells begin to reorganize into germ layers. The endoderm is the first to form, and begins forming in the human embryo at about two weeks after fertilization. By the fifth week, the endoderm has already differentiated into organs.
