I’m not going to comment in depth on the origin of uruk-hai, orcs, and orc-men. As the following links will show, uruk-hai were created by Sauron, uruk-hai are not the same thing as orc-men, and the fact that orcs were corrupted elves was disputed by JRR Tolkien, himself. This subject has already been done to death in the books section. Here are the pertinent links for your study.
The most informative is the following:
orcish fear
nulland here,and here,and here,and here.
Also a careful reading of the original text will answer your questions, especially the appendix to the RotK.
[ February 08, 2003: Message edited by: Bill Ferny ]