Trachea

Trachea is a hollow tubular organ serving to pass air into the lungs and from the lungs. In an adult, the trachea begins at the level of the lower edge of the sixth cervical vertebra, where it joins the larynx (at the level of the cricoid cartilage), and ends at the level of the upper edge of the V thoracic vertebra. The average length of the trachea in an adult is 12 cm (from 8.5 to 15 cm), the number of tracheal rings varies from 15 to 20 (the maximum number is 26). The width of the trachea varies from 17 to 19 mm.

In a child, the beginning of the trachea corresponds to the IV-V cervical vertebra, and the bifurcation of the trachea is at the level of the III-IV thoracic vertebra.

The minimum size of the trachea corresponds to the exhalation phase, the maximum to the inspiratory phase. With coughing, the tracheal lumen decreases 3-10 times, depending on the age of the person (the younger, the narrower the lumen of the trachea is).

The trachea is located in the anterior region of the neck (cervical section, pars cervicalis) and in the mediastinum of the thoracic cavity (thoracic region, pars thoracica)), the border between which passes along a transverse line drawn through the upper aperture of the thorax. The cervical spine is 1/3, and on the thoracic region it is 2/3 of the entire length of the trachea.

In topography, the trachea is closely connected with the organs of the anterior region of the neck. In front of the neck part of the trachea are the lower part of the thyroid gland, the pre-tracheal plate of the cervical fascia, the sternum-hyoid and the sternum-thyroid muscles of the neck. Back to the trachea is the esophagus. On each side there is a paired vascular-neural bundle, which includes the common carotid artery, internal jugular vein and the vagus nerve.

Bifurcation of the trachea is due to the arch of the aorta, the brachiocephalic trunk and the brachiocephalic vein, and to the initial part of the left common carotid artery. The posterior wall of the trachea extends all the way to the esophagus, from which it is separated by a layer of fiber. On the right and left between the trachea and the esophagus, esophageal and tracheal furrows are formed, in which the recurrent nerves and lower laryngeal arteries pass.

Along the trachea in front are the supragranular, interaponeurotic, pre-tracheal and paratracheal spaces. In the pre-tracheal cell space there is an unpaired venous plexus of the thyroid gland and in 10-20% of cases - an additional branch from the aorta that goes to the thyroid gland (the lower thyroid artery is a thyroidea ima). In the paratraheal tissue on the right are the lymph nodes, the vagus nerve, the cardiac branches of the border sympathetic trunk, to the left - the branches of the border trunk, the thoracic duct.

At the level V of the thoracic vertebra, the trachea is divided into the right and left main bronchi. In the place of division of the trachea, a fork - bifurcation (bifurcatio trachea) is formed. At the junction of the medial walls of the main bronchi, a small protrusion, called the spur, keel, or carina (carina tracheae) is revealed. The angle of bifurcation of the trachea is on average 70 °. During inspiration, the bifurcation of the trachea is displaced downwards and anteriorly by 2-3 cm.

The wall of the trachea consists of a mucous membrane, a submucosa, a fibrous-cartilaginous and adventitial membranes.

The mucous membrane of the trachea is lined with a pseudo-layered multi-row columnar (cylindrical) epithelium lying on the basal membrane. The composition of the epithelial cover is dominated by ciliate epitheliocytes, which have an average of 250 cilia. The movements of the cilia are directed upward, toward the larynx. In the integumentary epithelium of the trachea there is a significant number of goblet cells that secrete mucus. There are also basal (stem) cells, endocrinocytes (isolate norepinephrine, serotonin, dopamine) and some other types of epithelial cells. Own plate of the mucosa is rich in longitudinally arranged elastic fibers, lymphoid tissue. In the thickness of its own plate there are separate smooth myocytes, located mainly circularly. Through its own plate of the mucosa pass the excretory ducts of numerous glands of the trachea (gll.tracheales), the secretory sections of which are located in the thickness of the submucosa base.

The submucosa of the trachea, represented by a loose fibrous connective tissue, contains vessels, nerves, lymphoid cell clusters and individual lymphocytes.

The fibro-cartilaginous membrane of the trachea is represented by 16-20 hyaline cartilages (cartilagines tracheales). Each cartilage looks like an arc that occupies 2/3 of the circumference of the trachea and is not closed behind. Between themselves, the cartilages are connected by narrow annular ligaments (ligg.annularia), passing into the perichondrium, covering the cartilages of the trachea. The back membranous wall (paries membranaceus) of the trachea is formed by a dense fibrous connective tissue, contains bundles of myocytes. Outside the trachea is covered with an adventitious membrane.

Age traits of the trachea and major bronchi

In a newborn, the length of the trachea is 3.2-4.5 cm. The width of the lumen in the middle part is about 0.8 cm. The membranous wall of the trachea is relatively wide, the cartilages of the trachea are poorly developed, thin, soft. In the elderly and senile age (after 60-70 years), the cartilages of the trachea become dense, fragile, they break easily when compressed.

After birth, the trachea grows rapidly during the first 6 months, then its growth slows down and is again accelerated during puberty and in adolescence (12 years-22 years). By 3-4 years of life, the width of the lumen of the trachea increases by 2 times. Trachea in a child 10-12 years is twice as long as that of a newborn, and by 20-25 years its length is tripled.

The mucous membrane of the tracheal wall of the newborn is thin, tender; glands are poorly developed. The newborn trachea is located high. Its beginning is at the level of II-IV cervical vertebrae, and the bifurcation of the trachea corresponds to II-III thoracic vertebrae. In a child of 1-2 years, the upper edge of the trachea is located at the level of IV-V cervical vertebrae, in 5-6 years - anterior to the V-VI vertebrae, and in adolescence - at the level of the sixth cervical vertebra. Bifurcation of the trachea to 7 years of life of the baby is anterior to the IV-V thoracic vertebrae, and after 7 years it is gradually established at the level of the V thoracic vertebra, as in an adult.

The right main bronchus of the newborn departs from the trachea at a smaller angle (26 °) than the left (49 °), and in its direction is a continuation of the trachea. The main bronchi grow especially fast in the first year of the child's life and during puberty.

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