Topography and skeletotopy of the trachea
The trachea originates at the level of the VI–VII cervical vertebrae, being the direct continuation of the larynx (larynx). An interesting anatomical detail is that the position of the lower edge of this organ depends on sex: in men, it descends somewhat lower than in women.
When considering syntopy (neighborhood with other structures), it is important to distinguish the parts of the organ:
- In the cervical region, the respiratory tube is located strictly anterior to the esophagus.
- In the thoracic cavity, its anterior surface is covered by large blood vessels, while posteriorly it still lies adjacent to the esophagus, positioned anterior to it.
The overall dimensions of the organ average from 9 to 15 cm in length, and the transverse dimension (width) ranges within 1.5–2.7 cm.
Bifurcation and comparative anatomy of the main bronchi
Descending into the thoracic cavity, at the level of the IV–V thoracic vertebrae, the trachea divides into two branches. This site is called the tracheal bifurcation (bifurcatio tracheae). Internally, at the site of division, a ridge is formed — the carina of trachea (carina tracheae).
The right and left main bronchi (bronchi principales) depart from the bifurcation, each having its own distinct anatomical features.
| Sign | Right main bronchus (bronchus principalis dexter) | Left main bronchus (bronchus principalis sinister) |
|---|---|---|
| Dimensions | Shorter and wider | Longer and narrower |
| Angle of origin | Arises at a more obtuse angle | Arises at a more acute angle |
| Direction | Is a more direct continuation of the trachea | Departs more markedly to the side |
| Topography | — | Passes under the aortic arch (arcus aortae) |
Structure of the tracheal and bronchial walls
The walls of the trachea and the main bronchi branching from it have a specialized structure that ensures the constant patency of the lumen and uninterrupted airflow.
The framework of the tube is formed by hyaline cartilaginous rings (semi-rings) (cartilagines tracheales). They are incomplete posteriorly. The posterior wall is represented by the membranous part (paries membranaceus). It contains smooth muscle fibers that form the trachealis muscle (m. trachealis).
The inner surface of the respiratory tract is lined with a mucous membrane (tunica mucosa). Its main histological feature is the presence of pseudostratified ciliated epithelium, which, together with the secretion of mucous glands (glandulae tracheales, bronchiales), moistens and cleanses the inhaled air.
Briefly: answers to topical questions
Which organs and structures are adjacent to the trachea in the cervical region?
In the cervical region, the thyroid gland, esophagus, as well as vascular and nervous structures are adjacent to the trachea.
- Anteriorly — the isthmus of the thyroid gland, the unpaired thyroid venous plexus (plexus venosus thyroideus impar), in 6–8% of cases the a. thyroidea ima, and pretracheal lymph nodes (nodi lymphatici pretracheales).
- Laterally — the lobes of the thyroid gland, which embrace the lateral and partially the posterior wall of the trachea.
- Posteriorly — the anterior wall of the esophagus, with which the membranous part of the trachea is connected. The recurrent laryngeal nerves run in the tracheoesophageal grooves.
How many cartilaginous semi-rings form the framework of the trachea?
The framework of the trachea is formed by 16 to 20 cartilaginous semi-rings.
These structures are incomplete rings posteriorly, consisting of hyaline cartilage and forming part of the fibrocartilaginous coat of the organ. Posteriorly lies the membranous part (paries membranaceus), where the ends of the cartilaginous semi-rings are connected by bundles of smooth muscle fibers (m. trachealis). Lower, at the level of the bifurcation, the trachea transitions into the main bronchi, where the cartilaginous rings become complete.
What tissue layers make up the wall of the trachea?
The tracheal wall consists of four tissue layers (tunics).
- Mucous membrane (tunica mucosa) — lined with pseudostratified ciliated epithelium and contains mucous glands (glandulae tracheales).
- Submucosa — located beneath the mucous membrane.
- Fibrocartilaginous coat — includes hyaline cartilaginous semi-rings (cartilagines tracheales). Posteriorly lies the membranous part (paries membranaceus), containing smooth muscle fibers (m. trachealis).
- Adventitia — the outer connective tissue layer.
Which arteries supply blood to the trachea?
Blood supply to the trachea is provided by branches of several arteries.
- Inferior thyroid arteries (aa. thyroideae inferiores) — give off tracheal branches (rr. tracheales) to the cervical region.
- Unpaired lowest thyroid artery (a. thyroidea ima) — serves as an additional source of blood supply (occurs in 6–8% of cases).
Mediastinal and bronchial branches (rr. mediastinales, rr. bronchiales) also participate in the blood supply of the organ.
Where does lymph drainage from the trachea and main bronchi lead?
Lymph drainage from the trachea and main bronchi occurs into the system of regional lymph nodes of the thoracic cavity and neck.
The drainage pathway includes the following groups of nodes:
- Bronchopulmonary nodes (nodi bronchopulmonales).
- Tracheobronchial nodes (nodi lymphoidei tracheobronchiales) — divided into superior (superiores) and inferior bifurcation nodes (inferiores).
- Paratracheal nodes (nodi paratracheales).
- Mediastinal nodes — anterior and posterior.
The efferent vessels of the paratracheal nodes subsequently form the right and left bronchomediastinal trunks (trunci bronchomediastinales dexter et sinister).
To remember the differences of the right bronchus, use the "straight tube" rule: the right bronchus is wider, shorter, and forms a more direct continuation of the trachea, departing at an obtuse angle.
Class and exam questions
At what level does the trachea begin and end?
The trachea begins at the level of the VI–VII cervical vertebrae (as a continuation of the larynx) and ends with a bifurcation at the level of the IV–V thoracic vertebrae.
Which of the main bronchi is wider and shorter?
The right main bronchus (bronchus principalis dexter) is shorter and wider compared to the left one.
What is located posterior to the trachea?
In both the cervical and thoracic regions, the esophagus lies posterior to the trachea. For this reason, the posterior wall of the trachea lacks cartilage and is represented by the membranous wall.
What type of epithelium lines the inner surface of the trachea?
The inner surface of the trachea is lined with a mucous membrane featuring pseudostratified ciliated epithelium and numerous mucous glands.
What else to study on this topic
- Blood supply, venous and lymphatic drainage of the trachea
- Innervation of the trachea and main bronchi
- Further branching of the bronchi: lobar and segmental branches
- Syntopy of the aortic arch and the left main bronchus
- Histological structure of the respiratory mucosa
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