Trachea Anatomy and Dimensions

• Trachea, Latin for air vessel, is a wide tube in the midline within the lower neck and superior mediastinum.
• The upper end of the trachea connects to the lower end of the larynx.
• The isthmus of the thyroid gland covers the trachea in the neck.
• The trachea bifurcates into right and left principal bronchi at its lower end.

Dimensions of Trachea

• The trachea is 10 - 15 cm in length.
• The external diameter measures around 2cm in males, and 1.5cm in females.
• The lumen in living subjects is smaller than in cadavers.
• The lumen is approximately 3mm at one year of age.
• Throughout childhood, the lumen size, up to 12mm in adults, usually corresponds to age in years, with an increase of 1mm per year up to 12 years.

Relationships

• The upper end of the trachea is situated at the lower border of the cricoid cartilage at the C6 vertebra.
• The bifurcated lower end lies at the lower border of the T4 vertebra in cadavers, in front of the sternal angle.
• In living subjects, the bifurcation lies at the lower border of T6 vertebra, which descends further during inspiration.

Course

• The trachea is in the median plane for most of its length.
• Near the lower end, it deviates slightly to the right.
• The trachea passes slightly backwards following the curvature of the spine while running downwards.

Relations in Thorax (Anterior)

• Manubrium sterni.
• Sternohyoid and Sternothyroid muscles.
• Thymus remains.
• Left brachiocephalic and inferior thyroid veins.
• Aortic arch, brachiocephalic and left common carotid arteries.
• Some lymph nodes.

Relations in Thorax

• Posteriorly the esophagus and vertebral column
• The right side has the right lung and pleura, right vagus, and azygous vein.
• The left side has the arch of aorta, left common carotid and left subclavian arteries as well as, left recurrent laryngeal nerve.

Structure

• The trachea features a fibroelastic wall, which is supported by a cartilaginous skeleton of C-shaped rings.
• There are 16-20 rings.
• These rings make the tube convex anterolaterally.
• Posteriorly, the gap is closed by a fibroelastic membrane including transversely arranged smooth muscle, known as trachealis.
• The lumen contains ciliated columnar epithelium as well as mucous and serous glands.
• The widest ring is the 1st ring.
• The carina is a hook shaped triangular process extending upwards from the lower part of the last ring at the bifurcation surrounding the two bronchi.
• The ridge is guide for surgeons during bronchoscopic and other examinations.
• The cartilages prevent collapsing, keeping the trachea patent.
• Cartilages are deficient posteriorly for allowing expansion of oesophagus during swallowing.

Arterial Supply

• Inferior thyroid artery branch of thyrocervical trunk
• Bronchial arteries at the bifurcation of the trachea

Venous Drainage

• Drains into the inferior thyroid venous plexus.

Lymphatics

• Pretracheal and paratracheal lymph nodes.

Nerve Supply

• Parasympathetic innervation is from the right and left vagus nerves combined with the recurrent laryngeal nerves.
• Sympathetic innervation comes from the upper 4-5 thoracic segments of the spinal cords.

Applied Anatomy

• Tracheoesophageal fistula is a congenital condition with communication between the bifurcation of the trachea and esophagus.
• The carina helps in bronchoscopic examinations.
• Any foreign body through the trachea enters the right bronchus more easily because it is more vertical.
• The posterior part is flattened to aid food bolus passage through the oesophagus.

Tracheostomy

• Involves a midline incision with inferior retraction of the thyroid gland isthmus.
• For adults with severe laryngeal damage.
• For infants with severe airway obstruction.
• A tracheostomy tube is inserted through the 2nd tracheal ring.
• The trachea may be compressed by pathological enlargements of the thyroid, thymus, lymph nodes, and aortic arch that may cause dyspnoea, irritative cough, and husky voice.

The trachea, or 'air vessel,' is a wide tube in the lower neck and mediastinum, connecting the larynx to the principal bronchi. It measures 10-15 cm in length, with varying diameters in males and females. Its upper end is at the C6 vertebra, bifurcating at the T4 vertebra.