Chapter 4
Question 37-Indicate the embryonic origin of each tissue class.

There are three parts to the tissue classes of the embryonic region-
1)Ectoderm-This part of the tissue is the outer most part. It forms quickly after the cell is fertilized, and cell division starts to happen. It then turns into the spine, peripheral nerves, and brain. Also the tooth enamel, the epidermis and the lining of the mouth.

2)Mesoderm-This is the middle layer between the ectoderm and endoderm. This forms the connective tissue and the non epithelial red blood cells. It is different from the other layers because it has a intercellular signaling after the mesoderm is polarized by organizing center. The mesoderm eventually turns into the smooth, cardiac, and skeletal muscle cells, along with red blood cells and the tubule cells of the kidney.

3)Endoderm-It is the innermost layer. Cells migrate into the archenteron form the inner layer of the gastrula, which develops into the endoderm. It consists of flattened cells, which then eventually become columnar. It forms the epithelial lining of many systems. The endoderm will turn into the lung, thyroid, and pancreatic cell.