trachea(redirected from windpipe)
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an organ of the respiratory tract in vertebrates, including man, that is situated between the larynx and bronchi.
In amphibians, the trachea is not divided into bronchi, as the lungs start at the trachea. Nor is it separate from the larynx in all species; for example, it is absent in tailless amphibians, where the lungs start at the trachea. In tailed amphibians, the trachea is usually long and has paired cartilages that sometimes grow together.
In reptiles, birds, and mammals, the trachea is distinctly separate from the larynx and is divided into bronchi. The length of the trachea is directly proportional to the length of the neck and inversely proportional to the length of the bronchi. The trachea in reptiles consists of closed or horseshoe-shaped cartilaginous rings, while in birds it usually consists of closed, partially ossified rings, which in some species form numerous windings and widenings that together reverberate sound. In many birds, the lower rings form the syrinx.
In mammals, the trachea consists of cartilaginous half-rings; closed rings are found in beavers, agoutis, flying lemurs, and representatives of the genus Lemur. The dorsal side of the trachea is usually membranous and contiguous with the esophagus. In whales and Sirenia, the cartilages partly fuse together to form a type of spiral. The trachea is usually divided into two bronchi in the thorax. A supplementary bronchus usually branches off the trachea in toothed whales, ruminants, and swine.
The human trachea or windpipe is a direct continuation of the larynx. It is a tube 11–13 cm long, consisting of 16–20 cartilaginous half-rings that are joined by fibrous connective tissue. It is lined with a mucous membrane. The submucous layer contains many mixed mucous glands. Inflammation of the tracheal mucosa is called tracheitis.
(1) A respiratory organ of terrestrial arthropods in the form of an air-conveying tubule that threads through the body and opens at the body surface, forming a spiracle or stigma.
Tracheae are deep invaginations in the body surface and are lined with a thin layer of chitin, which forms a supportive spiral filament that prevents collapse of the tubule walls. In insects and solpugids, extremely slender branchings of the tracheae, tracheoles, thread through the entire body, entwining the organs and even penetrating the interiors of some cells. Thus, oxygen is delivered directly to the site where it is required, and gases are exchanged without the help of a circulatory system.
Many arthropods with highly developed tracheal systems make respiratory movements, such as rhythmic contractions and expansions of the abdomen. In more primitive myriapods and insects, almost all segments of the body have a pair of tracheal bundles and stigmata. In centipedes and most insects, bundles of tracheae that are at first independent later unite as larger longitudinal bundles to form a single respiratory system, and some segments lack stigmata. Many arachnids breathe by means of tracheae, for example, solpugids, phalangids, pseudoscorpions, and many spiders, ticks, and mites. The tracheae and stigmata of these arachnids are located in various parts of the body and are developed independently in the evolutionary process, so that they are not homologous. The tracheae of terrestrial arthropods of other classes also originated independently. In the Onycho-phora, primitive tracheae are represented by numerous bundles of extremely slender tubules, which open into a common stigma; the stigmata are distributed in more or less disorderly fashion throughout the entire body. Some oniscoideans have rudimentary tracheae in the form of tubular branched invaginations on the surfaces of the exopodites of the anterior abdominal legs.
(2) In plants, water-conveying vessels of the xylem.
REFERENCESDogel’, V. A. Sravnitel’naia anatomiia bespozvonochnykh, part 1. Leningrad, 1938. Pages 411–35.
Beklemishev, V. N. Osnovy sravnitel’noi anatomii bespozvonochnykh, 3rd ed., vol. 2. Moscow, 1964. Pages 54–60.
A. V. IVANOV