Epithelia are tissues consisting of closely apposed cells without intervening intercellular substances. Epithelia are avascular, but all epithelia "grow" on an underlying layer of vascular connective tissue. The connective tissue and the epithelium are separated by a basement membrane. Epithelium covers all free surfaces of the body. Epithelium also lines the large internal body cavities, where it is termed mesothelium. Furthermore, the internal surfaces of blood and lymph vessels are lined by epithelium, here called endothelium.
Epithelia are classified on the basis of the number of cell layers and the shape of the cells in the surface layer.
* If there is only one layer of
cells in the epithelium, it is designated simple.
* If there are two or more layers of cells, it is termed stratified.
* Cells in the surface layer are, as a rule, described according to their height as squamous (scale- or plate-like), cuboidal or columnar.
Psuedostratified epithelia appears to be layered (stratified) because the cell nuclei occur in two or more levels in a row of aligned cells
|Type of Tissue||Function||Location|
|Pseudostratified columnar||removing dust and particles from airways, has cilia||lines the respiratory passageways|
|Simple Columnar||Absorption||lines the uterus and most organs of the digestive tract|
|Simple Cuboidal||Secretion and Absorption||glands, kidney tubules, ovaries|
|Simple Squamous||Diffusion and Filtration||lungs, walls of capillaries and vessels|
|Stratified Squamous||Protects underlying cells||skin(keratinized) and the throat, vagina, mouth (soft)|
|Stratified Cuboidal||Protection||lines ducts of the mammary glands, sweat glands, pancreas|
|Stratified Columnar||Protection, secretion||male urethra and vas deferens, parts of the pharynx|
|Transitional (unstretched)||Specialized to become distended||urinary tract|
***Once your are comfortable with the types of epithelia, move onto the QUIZ. You may use your notes and drawings.