1 All Physician Training licenses expire on August 31, 2015, are good for three years, and can only renew once (for a total of six years). 2  All Physician Assistant licenses expire on January 31 of even-numbered years.  All Anesthesiologist Assistant licenses expire on January 31 of even-numbered years.
The epidermis is the uppermost or epithelial layer of the skin. It acts as a physical barrier, preventing loss of water from the body, and preventing entry of substances and organisms into the body. Its thickness varies according to body site. The epidermis consists of stratified squamous epithelium.
Epithelia are sheets of cells that provide the interface between masses of cells and a cavity or space (a lumen). 1  The portion of the cell exposed to the lumen is called its apical surface.  The rest of the cell (i.e., its sides and base) make up the basolateral surface.