Lungs get an assist from the body's built-in air filters.
Ciliated stratified columnar is a kind of epithelium, or tissue lining. Under a strong microscope, it looks like the fringe on a throw rug. In humans, this epithelium contains cilia, which look like tiny hairs but are actually tiny tubes. The ciliated stratified columnar protects the cilia and the cilia protect the animal. In humans, they're found in the trachea where they sweep clean the air we breathe.
Cilia
Cilia were once thought to be only mere hairs -- an evolutionary leftover, like the appendix or most of our body hair. Scientists now know that cilia are neither hairs nor unimportant. These cell protrusions are organelles -- a tiny part of a tiny cell that works on a small scale in the way that a multicellular creature's organs work on a much larger scale. Cilia can be sensors, eyes and ears monitoring the cell's environment, or act like arm and leg muscles, pushing objects around.
Covering
Any cell that comes into contact with a foreign substance needs protection. Cells lining the trachea, through which air passes to the lungs, have to deal with the dirt and other contaminants that breathed-in air contains. This protection lining the respiratory passages is called ciliated, because it follows the hairlike shape of the cilia it protects. It's called columnar for the same reason. And it's stratified because, in cross-section, like the rock layers of the Grand Canyon, it's different and distinguishable from the cell layer it's protecting underneath.
Folds
Our cilia take advantage of the same evolutionary trick employed by our brains: If you take a flat surface and fold it, there's a lot more surface in a given area. For brains, that helps maximize the processing power inside your skull; for cilia, which are really just folds in the cell's surface that trap contaminants and remove mucus, that helps maximize air filtration inside your trachea. The cilia still need protection, so the surface bends and folds, too.
Diseases
Without its covering, cilia and cell soon die. Without its cilia, which after all are tubes, there would be nothing to carry proteins from the cells to build the protective membrane -- and the cell dies. Scientists are only scratching at the surface, so to speak, of understanding the complex transactions that occur inside ciliated cells. They call this protein movement "intraflagellar transport," named after the flagellum, an anatomical cousin of cilia used by cells as tails or propellers to move around. DNA analysis of problem cilia in mice and other animals may lead to clues to dealing with similar problems in ailing humans.
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