Types of Epithelia: 

Simple epithelia: most concerned with absorption, secretion, and filtration, consist of a single cell layer and usually very thin. 

Simple Squamous Epithelium: flattened laterally, with a sparse cytoplasm. Fount where filtration of the exchange of substances by rapid diffusion is a priority. (kidneys, lungs) two types- endothelium provides slick friction reducing lining in lymphatic vessels and hollow organs, and mesothelium, the epithelium found in serous membranes lining ventral body cavity.

Simple Cuboidal Epithelium: single layer of cells, whose functions are secretion and absorption. Forms walls of smallest duct glands and many kidney tubules. 

Simple Columnar Epithelium: single layer of tall closely packed cells in a row. Lines digestive tract from stomach through the rectum. Mostly associated with absorption and secretion. Found on free surfaces, helping to move substances or cells through internal passageway. 

Pseudostratified Columnar Epithelium: cells vary in height, rest on the basement membrane, gives false impression that several cell layers are present. Secretes or absorbs substances, line most of the respiratory tract.