Fig. 1.1
Anterior view of the dissected trachea. Note the tracheal bifurcation angle of 60°, (1) anterior view: trachea and tracheal cartilage. (2) Tracheobronchial bifurcation. (3) Membranous pars or tracheal muscle. Unit of Human Anatomy and Embryology. Department of Pathology and Experimental Therapeutics. Universitat de Barcelona
The especial tracheal configuration and its elastic structure make it capable to elongate up to one third of its length. This fact is of particular interest for tracheal reconstruction surgeries.
Dimensions of the trachea vary primarily according to age and less so with gender. Figures 1.2, 1.3, 1.4, and 1.5 present the normal size variations in all three axes, internal size, area, and volume.
Fig. 1.2
Medium length of the trachea increases similarly in both genders until the age of 14. After that it only increases in men
Fig. 1.3
Medium tracheal diameter increases similarly in both genders until the age of 14. After that it only increases in men
Fig. 1.4
Medium tracheal area increases similarly in both genders until the age of 14. At age 20, tracheal area is 44.6% larger in men than in women
Fig. 1.5
Medium tracheal volume increases similarly in both genders until the age of 14. By age 20, men’s tracheal volume is 60% larger than women’s
Among both genders, there are also differences in tracheal size especially in the sagittal and transverse axes, which are evident in tomographies and 3D reconstructions (Figs. 1.6 and 1.7).
Fig. 1.6
: At age 20, men’s sagittal and transverse tracheal axes are 23% and 11.4% larger than women’s, respectively. Coronal computerized tomography: view of mediastinal trachea, tracheobronchial bifurcation, and main bronchi
Fig. 1.7
Medium tracheal diameter is 1.5 mm larger in men than in women. Medium bronchial diameter is 1 mm larger in men. 2D tomographic reconstruction of the tracheobronchial tree. Note that the intracarinal angle is 60°. Lengths are 5 cm for the left main bronchus and 2.5 cm for the right main bronchus
Internal Morphology
The tracheal tube has two covers or layers.
Fibro-Chondro-Elastic Layer
It is a completely circular, soft, and elastic connective tissue fundamental matrix. It affects the entire circumference of the windpipe. It presents tiny holes that represent the point of vascular entrance or exit to and from inside the trachea.
Enclosed to this layer, there are bands of incomplete hyaline cartilage rings, horseshoe shaped. The cartilage forms about four fifths of the circumference of the trachea. Given that the posterior border of the trachea is formed by a fibromuscular membrane, tracheal cross-sectional shape is similar to a letter D, with the flat side located posteriorly. The tracheal muscles cross transversely and obliquely, forming a continuum of entangled fibers which constitute a large muscle: the common tracheal muscle. Contraction of this muscle produces adduction of the free cartilage edges, thus modulating the internal tracheal caliber. Wrapping the outer tracheal tube, we found the adventitia, a membrane that acts as a false pretracheal fascia. Between the adventitia and the tracheal wall, vascular and nervous branches are located, and they incorporate to the tracheal tube wall at the level of the interchondral spaces.
Mucous Layer
The trachea is lined by pseudostratified columnar epithelium that sits in an elastic lamina propria and covers the inside of the tracheal tube. Goblet mucous cells and small subepithelial glands that secrete into the luminal surface are interspersed among the ciliated columnar cells. The produced mucus adheres to inhaled foreign particles, which are then expelled by the action of cilia propelling the mucus lining upward towards the pharynx from which they can be coughed and sneezed out of the airway. At the end of the tracheal duct, when it is divided into the main bronchi, the mucosa presents a middle line elevation known as carina, similar to a medial ridge. The tracheal carina indicates the entrance to the right and left main bronchus (Fig. 1.8a–c).
Fig. 1.8
(a) Cross section , trachea. (1) Respiratory cylindric epithelium and mucous glands. (2) Horseshoe-shaped cartilage, with a posterior opening. (3) Main layer, connective tissue fundamental matrix, surrounded by the adventitia. (b) Schematic illustration of the elements of the tracheal wall. (1) Poli-pseudostratified columnar epithelium, (2) gland drainage orifice, (3) gland duct, (4) submucous, (5) vagus nerve, (6) venules and arterioles. (c) Tracheal mucous gland. (1) Arteriole, (2) erythrocyte, (3) endothelial cell, (4) basement membrane, (5) Golgi apparatus of a goblet cell, (6) endoplasmic reticulum, (7) vacuole, and (8) mucus secretion
Blood Supply
Arterial—it is established by two arterial systems on each side of the trachea, communicating the aorta artery with the subclavian artery:
From the aorta, the left paratracheal ascending artery (Demel arteries) and the tracheobronchial esophageal artery. Of the latter, the right bronchial artery, the esophageal artery, and the right paratracheal ascending artery are born.
From both subclavian arteries and inferior thyroid arteries and from these in turn emerge the right and left paratracheal descending arteries (Haller arteries).
Each paratracheal descending artery anastomoses with the paratracheal ascending artery of the corresponding side, closing the vascular circuit at the back of the tracheal wall and along its side edges. From these two vascular axes, tracheal perforating arteries are born that supply tracheal layers entering through the interchondral spaces.
Anatomo-Clinical Relationships
The trachea is related to their surroundings through the peritracheal fascia, as if it were a hanger between the neck and the mediastinum. Vascular and nerve structures hung from or are in contact with it.
Regardless of the anatomical details, the tracheal relationships from inside out are:
Posterior: recurrent nerve, esophagus, and vertebral bodies covered by the deep cervical aponeurosis
Anterior: thyroid gland, medium cervical aponeurosis, anterior jugular veins, and superficial cervical aponeurosis
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