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 two major types of epithelial cells found in alveoli (pneumocytes): 1  Type I (Squamous Alveolar) cells: These form the structure of an alveolar wall. 2  Type II (Great Alveolar) cells: These are the site of surfactant production in the lungs, making them critical for maintaining the elastic recoil of the lung.