Respiratory tract
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2008-06-15T03:02:07Z
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Replaced image with similar one... however, it doesn't require references!
[[Image:Respiratory system complete numbered.svg|thumb|right|250px]]
In humans the '''respiratory tract''' is the part of the [[anatomy]] that has to do with the process of [[Respiration (physiology)|respiration]].
The respiratory tract is divided into 3 segments:
*[[Upper respiratory tract]]: [[nose]] and nasal passages, [[paranasal sinus]]es, and [[throat]] or [[pharynx]]
*Respiratory airways: [[voice box]] or [[larynx]], [[Vertebrate trachea|trachea]], [[bronchus|bronchi]], and [[bronchiole]]s
*[[Lung]]s: [[respiratory bronchiole]]s, [[alveolar duct]]s, [[alveolar sac]]s, and [[alveoli]]
The respiratory tract is a common site for infections. [[Upper respiratory tract infection]]s are probably the most common infections in the world.
Most of the respiratory tract exists merely as a piping system for air to travel in the lungs; [[alveoli]] are the only part of the lung that exchanges [[oxygen]] and [[carbon dioxide]] with the [[blood]].
Moving down the respiratory tract starting at the trachea, the tubes get smaller and divide more and more. There are estimated to be about 20 to 23 divisions, ending up at an alveolus.
Even though the cross-sectional area of each bronchus or bronchiole is smaller, because there are so many, the total surface area is larger. This means there is less resistance at the terminal bronchioles. (Most resistance is around the 3-4 division from the trachea due to turbulence.)
==General histology==
The respiratory tract is covered in an [[epithelium]], the type of which varies down the tract. There are [[gland]]s and [[mucus]] produced by [[goblet cell]]s in parts, as well as [[smooth muscle]], [[elastin]] or [[cartilage]].
Most of the epithelium (from the nose to the bronchi) is covered in pseudostratified columnar [[cilia]]ted [[epithelial cell]]s, commonly called [[respiratory epithelium]]. The cilia beat in one direction, moving mucus towards the throat where it is swallowed. Moving down the bronchioles, the cells get more cuboidal in shape but are still ciliated.
Cartilage is present until the small bronchi. In the trachea they are C-shaped rings, whereas in the bronchi they are interspersed plates.
Glands are abundant in the upper respiratory tract, but there are fewer lower down and they are absent from the bronchioles onwards. The same goes for goblet cells, although there are scattered ones in the first bronchioles.
Smooth muscle starts in the trachea, where it joins the C-shaped rings of cartilage. It continues down the bronchi and bronchioles which it completely encircles.
Instead of hard cartilage, the bronchi and brochioles have a lot of elastic tissue.
Summary:
Upper respiratory tract - nose, pharynx & asscociates structures
Lower respiratory tract - larynx, trachea, bronchi & lungs
==References==
*[http://www.kcom.edu/faculty/chamberlain/Website/lectures/syllabi3.htm Syllabus: Infectious Diseases] see Respiratory Tract Infections by Neal Chamberlain, PhD. Kirksville College of Osteopathic Medicine, Missouri, USA
==See also==
*[[respiratory system]]
[[Category:head and neck]]
[[Category:Respiratory system]]
[[de:Atemtrakt]]
[[fr:Voies respiratoires]]
[[ko:숨길]]
[[la:Apparatus respiratorius]]
[[zh:呼吸道]]