- Respiratory tract
In humans the respiratory tract is the part of the
anatomy that has to do with the process of respiration.The respiratory tract is divided into 3 segments:
*Upper respiratory tract :nose and nasal passages,paranasal sinus es, andthroat orpharynx
*Respiratory airways:voice box orlarynx , trachea, bronchi, andbronchiole s
*Lung s:respiratory bronchiole s,alveolar duct s,alveolar sac s, andalveoli 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 exchangesoxygen andcarbon dioxide with theblood .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 aregland s andmucus produced bygoblet cell s in parts, as well assmooth muscle ,elastin orcartilage .Most of the epithelium (from the nose to the bronchi) is covered in pseudostratified columnar
cilia tedepithelial cell s, commonly calledrespiratory 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 structuresLower 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
ee also
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respiratory system
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