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.
There are three sub-layers within the epidermis itself: the outer stratum corneum, the middle squamous cell layer, and the bottom basal cell layer. The stratum corneum is the visible part of the epidermis and is actually a layer of dead skin cells immediately on the skin's surface. This layer uses a protein called keratin to form a tough barrier between the outside world and the more vulnerable cells inside the skin and body.