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.
The following types of cells make up the epidermis: 1  Basal cells are at the bottom of the epidermis and continually reproduce to form new keratinocytes.  Keratinocytes or squamous cells are in the middle layer of the epidermis and produce keratin, the protein that forms the protective outer layer.