37) The Origin of the Tissue Classes and Critical Thinking Questions 1 & 2

One of the first events of embryonic development is the formation of the three primary germ layers: ectoderm, mesoderm and endoderm. These primary germ layers then specialize to form the four primary tissues from which all body organs are derived.
-The epithelial tissues form from all three germ layers: most mucosae forms from the endoderm, the endothelium and mesothelium form from the mesoderm and the epidermis forma from the ectoderm.
-The muscle and connective tissue develop from the mesothelium, and the nervous tissue develop from the ectoderm.
By the end of the second month of development, all of the primary tissues have appeared and all the major organs are in place.


1) No, John will not have a quick recovery because a torn knee cartilage is a severe injury and will take a few
weeks to months to recover. To repair the tissue his cells will have to go through regeneration and fibrosis and because his torn cartilage will have some scar tissue at the end of his recovery, his knee may not be the same and his football skills may decrease. Depending on the severity, John may even need physical thearpy.

2) The epithelium is better suited for protecting the body's external surface because it is made up of stratified epithelia which consists of two or more cell layers stacked on top of the other. Stratified Epithelia are common in high-abrasion areas where protection is important. The mucosa consists consists of simple epithelia which is composed of a single cell layer and typically found where absorption and filtration occur. Because the simple epithelia in mucosa only have a single cell layer, the mucosa is not the best suited for protecting the body 's external surface.