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Trachea

life science Maturity 9-11 Next article →

The trachea, often called the windpipe, is a vital cartilaginous tube in the respiratory tract.

Blausen 0865 TracheaAnatomy
Blausen 0865 TracheaAnatomy

It serves as the main passageway for air traveling between the larynx and the lungs. In almost all land vertebrate animals, this structure is essential for breathing. It connects the larynx, or voice box, to the two primary bronchi of the lungs. Without a functional trachea, oxygen could not reach the lungs to sustain life.

3d-vh-m-trachea
3d-vh-m-trachea

To function effectively, the trachea must remain open while also being able to move. It is constructed from 16 to 20 C-shaped rings of hyaline cartilage. These rings are approximately 4 millimeters high in adults. Because the rings are incomplete and C-shaped, they do not form a solid circle. Instead, the open ends are joined vertically by overlying ligaments and the trachealis muscle. The trachealis muscle runs along the back wall of the trachea. This muscle can contract during a cough to reduce the size of the lumen, which is the inner space of the tube. Additionally, an outer layer of connective tissue called adventitia allows the trachea to bend and stretch during body movements.

The internal environment of the trachea is highly specialized for protection. The trachea is lined with an epithelium of column-shaped cells. These cells feature tiny, hair-like extensions known as cilia. Scattered among these are goblet cells, which are glandular cells that produce mucins. Mucins are the main components of mucus. This mucus works to moisten and protect the airways by trapping inhaled dust and foreign particles. The cilia then perform a process called mucociliary clearance. They waft the mucus and trapped particles upward toward the larynx and pharynx. From there, the material is either swallowed or expelled as phlegm.

Development of the trachea begins very early in the human life cycle. During the fourth week of embryo development, the respiratory bud grows and the trachea begins to separate from the foregut. This separation is caused by the formation of ridges known as the tracheoesophageal septum. By the fifth week, the left and right main bronchi begin to form as buds at the end of the trachea. In the first year of life, the trachea is quite small, measuring no more than 4 millimeters in diameter. By late childhood, it expands to an adult diameter of approximately 2 centimeters. In children, the trachea is generally more circular and vertical than in adults.

An adult trachea has specific anatomical landmarks and dimensions. It begins at the lower edge of the cricoid cartilage of the larynx at the level of the sixth cervical vertebra (C6). It ends at the carina, which is the specific point where the trachea branches into the left and right main bronchi. This branching occurs at the level of the fourth thoracic vertebra (T4). While the trachea is a midline structure, its position can change with breathing. It may also be displaced to the right by the aortic arch. In adults, the trachea is also wider in males than in females.

The trachea is surrounded by many critical structures in the neck and chest.

Gray622
Gray622

The thyroid gland stretches across the upper trachea, with its isthmus overlying the second to fourth rings. Nearby, the aortic arch and the left common carotid artery pass close to the lower trachea. Behind the trachea sits the esophagus, followed by the vertebral column. Blood is supplied to the trachea through small branches from the inferior thyroid arteries and the bronchial arteries. These arteries split into superior and inferior branches to supply the anterior and posterior parts of the tube. The lymphatic system also serves the area, draining into the pretracheal and paratracheal lymph nodes.

Medical issues can significantly impact tracheal function. Inflammation of the trachea is called tracheitis. This is often caused by viral infections, such as parainfluenza or influenza viruses. Bacterial infections, which can be caused by *Staphylococcus aureus* or *Streptococcus pneumoniae*, can also cause tracheitis. These infections may lead to swelling that narrows the airway. This narrowing often produces a harsh breathing sound called stridor.

If the trachea becomes completely obstructed, a tracheostomy may be required. During surgery, doctors may perform tracheal intubation, which involves inserting a tube into the trachea to assist with mechanical ventilation.

It is interesting to note that the term "trachea" describes different structures in different animals. In insects, the trachea is part of a completely different respiratory system.

Tracheal system of dissected cockroach
Tracheal system of dissected cockroach

Instead of using lungs, insects use a system of spiracles, tracheae, and tracheoles. This system transports metabolic gases directly to and from their tissues. This highlights how evolution has developed various ways to solve the challenge of gas exchange across the animal kingdom.

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File:Blausen 0865 TracheaAnatomy.png
Blausen 0865 TracheaAnatomy.png
File:Gray622.png
Gray622.png
Stridor NP OGG 2.ogg
File:Tracheal diverticulum.png
Tracheal diverticulum.png
Tracheal system of dissected cockroach.tif
Cockroach tracheae supplying crop.tiff
3d-vh-m-trachea.stl
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