Ciliated cells are cells covered in tiny hair-like projections known as cilia. The name cilia is derived from the Latin term for "eyelash" because of their resemblance to the tiny projections extending from the cell membrane. Cilia work by rhythmically moving back and forth in unison. These tiny projections allow the cell to move through liquid or mucus environments or to propel objects around themselves, such as food, dust, or bacteria.
Single-celled organisms and ciliated epithelial cells found in many types of animal tissues can be referred to as ciliated cells. Ciliated epithelial cells are, however, rarely found in plants. One possible evolutionary explanation for this might have to do with the loss of moisture. Cilia dramatically increase the surface area of a cell, increasing the chance for evaporation and the need for water. Cycads, a type of tropical tree, are one of the few plant genera that possess ciliated cells.
In animals, ciliated epithelial cells are commonly found in many parts of the body. The brain, for example, uses ciliated cells to help circulate cerebrospinal fluids through the brain and spinal column. Research conducted in 2007 by Victor Chizhikov, Ph.D., and Kathleen Millen, Ph.D., showed that ciliated cells are vital for normal brain development in the cerebellum as well.
Ciliated cells are also used in the oviducts to move the ova to the uterus and in the respiratory system to eliminate dust and germs from nasal passages. The ciliated cells in the respiratory system are the primary cells affected by respiratory viruses, such as the cold or flu. These viruses work by killing the cell completely or by paralyzing the cilia. This causes mucus and bacteria to accumulate, leading to such secondary infections as sinusitis or bronchitis.
When referring to single-celled organisms, ciliated cells comprise a very important group of protists, with thousands of documented species. These protists are considered the most complex single-celled organisms known and are very important to aquatic environments. Protists vary in their ability to tolerate pollution and are often used as an indicator species to quickly measure the health of a body of water.
Cilia are made of microtubules, which are thick spirals of tubulin, and are covered by the cell membrane. Cilia are often confused with flagella due to the numerous similarities, but there are key differences between the two. The primary difference is in regard to the number of projections. Cilia refer to multiple projections from a single cell whereas flagella refer to a single projection from one cell. The whip-like tails of sperm and giardia cells are excellent and easily recognizable examples of flagellate cells.
