Crossword Dictionary

TRACHEA 

Trachea, in vertebrates and invertebrates, a tube or system of tubes that carries air. In insects, a few land arachnids, and myriapods, the trachea is an elaborate system of small, branching tubes that carry oxygen to individual body cells; in most land vertebrates, the trachea is the windpipe, which conveys air from the larynx to the two main bronchi, with the lungs and their air sacs as the ultimate destination. In some birds, such as the swan, there is an extra length of tracheal tube coiled under the front of the rib cage. The cartilaginous structures that ring most mammalian tracheae are reduced to small irregular nodules in amphibians.

In man the trachea is about 15 centimetres (6 inches) long and 2 to 3 centimetres in diameter. The trachea serves as passage for air, moistens and warms it while it passes into the lungs, and protects the respiratory surface from an accumulation of foreign particles. The trachea is lined with a moist mucous-membrane layer composed of cells containing small hairlike projections called cilia. The cilia project into the channel (lumen) of the trachea to trap particles. There are also cells and ducts in the mucous membrane that secrete mucus droplets and water molecules. At the base of the mucous membrane there is a complex network of tissue composed of elastic and collagen fibres that aid in the expansion, contraction, and stability of the tracheal walls.