The trachea, commonly called the windpipe, is the air passage-way from the mouth to the lungs. Non-fish vertebrae all have a trachea. The moist with mucus walls of the tube-like structure trap inhaled particles to keep them from entering the lungs.
The trachea is an open-ended cylindrical structure that starts at the larynx and ends at the bifurcation. It is about one inch in diameter and can run four to six inches in length. Within the pipe there are anywhere from 15 to 20 c-shaped cartilage rings to stabilize the walls. A trachealis muscle runs vertically along the back of the trachea. It is connected to each of the c-shaped rings and can contract the entire set of rings during actions such as coughing or swallowing. During swallowing, the structure slightly collapses in order for food boluses to pass through the esophagus located behind the trachea. The opening of the trachea is protected by the epiglottis which closes when matter is in transit to the esophagus.
The inside of the structure is lined with respiratory epithelium and goblet cells. These two groups of cells are able to produce mucus, use that mucus to catch foreign particles and then expel those particles by moving it out of the trachea with hair-like cilia. Once it reaches the pharynx, a small gag-like reflex will trigger the choice to expel or swallow phlegm.
Any obstruction or damage in the trachea can lead to respiratory failure.
Image Caption: Conducting passages of the human respiratory system. Credit: Lord Akryl/Wikipedia