Columnar epithelial cell
|Columnar epithelial cell|
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Columnar epithelial cells are epithelial cells whose height are at least four times their width. Columnar epithelia are divided into simple (or unilayered), and stratified (or multi-layered). These cells are tall and are arranged like pillars. They are found in the inner lining of the intestine. They secrete digestive enzymes and absorb digested food. Form follows function in biology, and columnar morphorphology hints at the functions of the cell. Columnar cells are important in absorption and movement of mucus. The cells may or may not bear microvilli (involved in maximizing the surface area for intestinal absorption) or cilia (involved in moving mucus and trapped material up the respiratory passages to be expectorated or swallowed). Columnar epithelium may be simple or stratified. Simple columnar epithelium is most common and involves one layer of cells attached to a basement membrane. The nucleus is closer to the basal aspect of the cell than the apical aspect. Single stratification tends to indicate absorptive function. Stratified columnar epithelium is rare but can be found in salivary glands. It consists of a layer of columnar epithelium resting on top of at least one other layer of epithelial cells, which may have any shape (columnar, cuboidal, or squamous). Stratification in cuboidal tissue has a secretory function.
Simple columnar epithelia
Simple columnar epithelium is uni-layered and can be further subdivided into two categories; ciliated and non-ciliated. Ciliated columnar epithelium moves mucus and other substances via cilia and is found in the upper respiratory tract, the fallopian tubes, the uterus, and the central part of the spinal cord. Non-ciliated Simple columnar epithelium is found lining sections of the gastrointestinal tract, including the stomach, small intestine, and large intestine, and may be brush bordered.
Stratified columnar epithelia
Stratified columnar epithelia is a rare type of epithelial tissue composed of column shaped cells arranged in multiple layers. It is found in the ocular conjunctiva of the eye, in parts of the pharynx and anus, the female's uterus, the male urethra, vas deferens and lobar ducts in the salivary glands.
Pseudostratified columnar epithelia
Pseudostratified epithelium is a type of epithelium that, though comprising only a single layer of cells, has its cell nuclei positioned in a manner suggestive of stratified epithelia. As it rarely occurs as squamous or cuboidal epithelia, it is usually considered synonymous with the term pseudostratified columnar epithelium.
The term pseudostratified is derived from the appearance of this epithelium in section which conveys the erroneous (pseudo means almost or approaching) impression that there is more than one layer of cells, when in fact this is a true simple epithelium since all the cells rest on the basal lamina. The nuclei of these cells, however, are disposed at different levels, thus creating the illusion of cellular stratification. Not all ciliated cells extend to the luminal surface; such cells are capable of cell division providing replacements for cells lost or damaged.
Pseudostratified epithelia function in secretion or absorption. If a specimen looks stratified but has cilia, then it is a pseudostratified ciliated epithelium, since stratified epithelia do not have cilia.