Trachea - Anatomy & Physiology

Introduction

The trachea is the tube linking the cricoid cartilage of the larynx to the bronchi, forming part of the conducting system which transports air from the external environment to the lungs. The oesophagus lies dorsally to the trachea. The cervical part of the trachea lies generally in the median position, although this varies slightly depending on the position of the head. The thoracic part of the trachea crosses the aortic arch, thus its positioning is moved slightly to the right at this level. The trachea bifurcates to form the two bronchi at the level of the 4th-6th intercostal space.

Structure

The trachea contains numerous rings of hyaline cartilage which are C-shaped, being dorsally incomplete, connected to each other by elastic connective tissue. The ends of the incomplete rings are joined by the smooth trachealis muscle. The structural conformation of the trachea prevents collapse due to traction forces, whilst allowing it to adjust in length and diameter, as the neck moves and the diaphragm contracts. The trachea's walls are made up of a number of layers including the inner mucosa, fibrocartilaginous middle layer, and adventitia (in the neck) or serosa (in the thorax). The inner mucosa contains glands which produce mucus. This mucus traps debris and is constantly moved upwards towards the oropharynx where it is swallowed. This mechanism is known as the Muco-Ciliary escalator.

Function

The trachea is responsible for transporting air for respiration from the larynx to the bronchi.

Species Differences

In the dog and cat the C-Shaped rings are joined by muscle which is placed externally, rather than internally as is normal for the other species. In avian species the trachea is composed of tightly stacked rings of cartilage, which are complete with no dorsal space. They overlap considerably. The respiratory systems of non-homeotherms are also very different to that of mammals.

Histology

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  A histology section of a trachea (rat) _{©RVC 2008}

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  A histology section of the tracheal wall (rat) _{©RVC 2008}

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  A histology section of the epithelial lining of the tracheal wall (rat) _{©RVC 2008}

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  A histology section of the tracheal wall stained for elastic fibres (Cat)

  _{©RVC 2008}]]

Links

Click here for information on trachea pathology.

Click here for information on the syrinx and avian vocalisation.

References

Dyce, K.M., Sack, W.O. and Wensing, C.J.G. (2002) Textbook of Veterinary Anatomy. 3rd ed. Philadelphia: Saunders.