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The respiratory tract is divided into 3 segments:
The respiratory tract is a common site for infections. Upper respiratory tract infections 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 bloodBlood is a circulating tissue composed of fluid plasma and cells ( red blood cells, white blood cells, platelets). Medical terms related to blood often begin in hemo or hemato ( BE: haemo and haemato from the Greek word for "blood". Blood of different spe.
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.)
The respiratory tract is covered in an epitheliumIn zootomy, epithelium is a tissue composed of epithelial cells. Such tissue tends to surround parts of the body, somewhat like a cell membrane. It is also used to form glands. The epithelium is usually the layer of cells 'closer' to the outside world., the type of which varies down the tract. There are glandA gland is an organ in an animal's body that synthesizes a substance for release, often into the bloodstream ( endocrine gland) or into cavities inside the body or its outer surface ( exocrine gland). Humans have a large variety of glands, from the pituits and mucusMucus is a slippery secretion of the lining of various membranes in the body ( mucous membranes). Mucus aids in the protection of the lungs by trapping foreign particles that enter the nose during normal breathing. Additionally, it prevents tissues from d producing goblet cell s in parts, as well as smooth muscleSmooth muscle is a type of non- striated muscle, found within the " walls" of hollow organs; such as blood vessels, bladders, uteri. gastrointestinal tracts, Smooth muscle is used to move matter withintraction|contraction]]; it generally operates " involu, elastinElastin is a protein in connective tissue that is elastic and allows skin to return to its original position when it is poked or pinched. or cartilageCartilage is a translucent dense connective tissue. In the adult, cartilage contains no blood vessels or nerves, and consists of a relatively homogeneous extracellular matrix, in which cells called chondrocytes are sparsely distributed. These cells are re.
Most of the epithelium (from the nose to the bronchi) is covered in pseudostratified columnar ciliated epithelial cells. 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 brochi and bronchioles which it completely encircles.
Instead of hard cartilage, the bronchi and brochioles have a lot of elastic tissue.