noun, plural: columnar epithelia
The epithelial tissue (also called epithelium) is one of the different types of animal tissues. It is made up of one or more layers of cells closely packed together. It is primarily involved in protecting the underlying structures, secretion, regulation, and absorption. This tissue may be classified histologically according to the cell shape. The different types of epithelia based on the cell shape are: (1) squamous epithelium, (2) columnar epithelium, and (3) cuboidal epithelium.
The columnar epithelium is composed of epithelial cells that are column-shaped. The cell comprising the columnar epithelium is taller than it is wide. Its height is approximately four times its width. The nucleus in each cell is elongated and often found near the base. Some of them may have microvilli at the apical surface. When present, the microvilli increase the surface area (such as during absorption). Cilia may also be present. Ciliated columnar cells aid in the movement of mucus (as seen during mucociliary clearance).
The columnar epithelium may be classified according to the number of layers that make it up. For example, a simple columnar epithelium is one that which is made up of a single layer of columnar epithelial cells. A stratified columnar epithelium is comprised of more than one layer of columnar epithelial cells. A special type of single columnar epithelium is the so-called pseudostratified. Its name is derived from its appearance. It seems it is a stratified type of epithelium but in truth is it is comprised of only one layer of cells. The cells are oriented in a way that they appear to be in multiple layers when in fact there is only one layer of epithelial cells.
- columnar epithelial tissue