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.
Two more specialized cell types are also found in the epidermis: guard cells and trichomes. Guard cells are kidney-shaped cells that are filled with chloroplasts. They always occur in pairs and form a small pore between them. The pair of guard cells and their pore is called a stomate and functions in gas exchange.