Ciliated epithelium is a type of bodily tissues that is lined with “ciliated” cells, which are basically cells that have small, hair-like protrusions known as “cilia” that can either help the cells move along the tissue or can help debris and waste move along the surface of the cells. Cilia typically move in one direction in a wavelike pattern, which allows the cells to sweep away debris, direct the flow of particles, and create a current. Tissues in this category are most common in the nasal and respiratory passageways, and are one of the main reasons mucus flows and carries out dead cells when a person has a cold. They occur in many places, though, including the brain, digestive system, and reproductive tract. Scientists usually categorize this sort of epithelium based on where exactly it is, as well as its main function.
Where It’s Found
This type of epithelium is found most often in the body’s air passages, including the lungs, trachea, and nose. In these places it works to keep dust and debris out of the lungs, essentially filtering the air a person breathes at a very basic level; it also controls the flow of mucus. Mucus is an important part of healthy respiration, but is particularly essential during periods of illness or viral infection. Proper mucus flow is one of the best tools the body has when it comes to flushing out illness. Particles in the air are trapped by the mucus in these passageways, and the sweeping motions of the cilia direct the mucus away from the lungs and out of the body.
Many different places in the human body have this sort of tissue. It is particularly useful anywhere where precise and organized movement is useful, including the digestive tract and the female reproductive system, which is responsible for moving unfertilized eggs from their source in the fallopian tubes to the uterus, where they have a better chance of becoming fertilized. Gravity can play something of a role in both cases, as can regular muscular contractions; coordinated cell movement at the tissue level is often also really helpful, though.
This tissue helps circulate cerebral fluids in the ventricles of the brain, too. Regular flow of fluid helps the brain stay healthy, protected, and able to conduct and relay signals efficiently. The cells in this region are almost always moving in a coordinated, synchronized way and provide a regular “current” in the head.
What It’s Made Of
In most cases the epithelium itself is made up of regular smooth tissue and is structurally similar to most other internal body tissues. The biggest differentiating characteristic is the presence of ciliated cells. The cilia on the edges of the cells are made up of microtubules, which are long protein strands known as filaments that make up a cell’s cytoskeleton, giving it structure. These microtubules bind together to form dimers, or pairs, which then associate with each other into a cylindrical shape for more strength. These tubes are held together by linking proteins, and they extend up through each of the cilium hairs on the surface.
The sweeping movements of the cilia are energy-dependent, and they rely on enzymes that use adenosine triphosphate to generate motion. These enzymes connect to the cell’s fibers and essentially “whip” them in one direction, allowing for the cilia’s characteristic pulsing waves.
The classification of ciliated epithelium is based on several factors, including location, cell shape, and overall appearance of the tissue as a whole. In general this sort of tissue is only found on the inner surfaces of the body, so it is part of the endothelium, or internal epithelium. The shape of individual cells is generally cylindrical, like a column, which means that this tissue is also usually part of the “columnar epithelium” category.
Appearance of Stratification
This sort of tissue is almost always smooth and uniform on the surface, though there are times when it can look striped or textured. The cells’ nuclei are sometimes positioned unevenly, which can give the tissue the appearance of having multiple layers — a condition called “stratification.” When this happens the tissue is best categorized as “pseudostratified epithelium,” or epithelium that appears to be stratified but is not. Terms can be combined for complex tissues, for example to form the more specific category, “ciliated pseudostratified columnar epithelium.”