In a Nutshell

• Size

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  • 1.3- 2.5cms in the male and from 1-2.1cms in the female
    • Tracheomalacia

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• Shape

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• Position

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• Character
  • Amyloidosis of the Trachea

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  Tracheobronchial Papillomatosis caused by Infection with Human Papillomavirus

  

• Time

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The trachea is a tubular portion of the respiratory system that connects the larynx to the bronchi.  It is relatively thin walled, about 6 inches long in the adult, consists of a series of c-shaped cartilagenous rings anteriorly and a membrane posteriorly.  At the level of the carina it divides into left and right bronchi.

Parts

Principles

Diameter

The mean transverse dimension of the trachea is 1.6cm, ranging from 1.3- 2.5cms in the male and from 1-2.1cms in the female.  The mean A-P dimension is slightly less, measuring 1.4cm.   

Consideration of the size of the conducting system as a tubular and transporting system where diameter and length are functionally relevant is far different from the considerations given to the gas exchange system where surface area is the prime functional consideration.  Measurements of the larger airways have practical significance for the bronchoscopist who has to know how far it is possible to advance the bronchoscope into the airways, for the anesthesiologist who needs to intubate the patient, and for the interventionalist who may need to stent a stenotic segment.  The smaller airways are more difficult to measure but in general they should approximate the size of the accompanying arteries.

The trachea, although it is a tube, is made up of 15-20 C-shaped cartilaginous rings with a posterior membranous surface, giving it a horseshoe shape in cross section. Its AP dimension is thus longer than its transverse dimensions.

The shape of the tracheobronchial tree at large is very similar to a branching tree.  If you took an image of the tracheobronchial tree and turned it upside down you would see the following;

 

It has an irregular dichotomous branching pattern meaning it divides into paired branches of unequal length and diameter.   The dichotomous branching pattern mirrors the branches of a tree.   Similarly if you took the illuminated bare trees on Michigan Avenue in Chicago at RSNA, and turned them upside down you would see the following 

Applied Anatomy 

Once we move beyond the trachea into the rest of the tubular system, the rounded cross sectional shape is at first maintained by full circle cartilage and then by muscle. The irregular dichotomous branching pattern is maintained.

 

We have noted the normal horseshoe shape of the trachea.  In COPD the tracheal A-P dimension increases relative to its transverse dimension, and the trachea assumes the shape of a “sabre” and is known as a “sabre trachea .

 

Position of the Trachea

The trachea is central in its position, and lies anterior to the esophagus.   It originates below the pharynx and ends at the carina where it bifurcates into left and right main stem bronchi.

The tracheobronchial tree changes its morphology (and so its nature) as it progresses from a relatively rigid cartilaginous structure strengthened by C-shaped cartilages.  The cartilage accompanies and supports the bronchi but disappears at the level of the bronchioles. The structure of the walls progresses to muscular, elastic, and mucus secreting bronchioles and then to delicate one cell layered airways at the alveolar level.  The bronchi contain cartilage the bronchioles do not

Applied Anatomy

Tracheomalacia is softening of the tracheal cartilages which results in relative collapse of the trachea during inspiration and thus affecting airflow.  The cause can be due to congenital weakening of the cartilage, due to extrinsic disease such as vascular rings and slings, or acquired from prolonged intubation or chronic infection. (eMedicine).

Amyloid Involvement

Links and References

Tracheal disease

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