Trachea

The trachea is an essential air-conducting tube of the respiratory system that connects the larynx to the bronchi, ensuring the passage of air to and from the lungs.

The trachea is a flexible and semi-rigid tube that extends from the cricoid cartilage of the larynx to the tracheal carina, where it divides to form the left and right main bronchi. Its structure is kept open by a series of C-shaped, incomplete tracheal cartilage rings. These rings are connected by fibroelastic annular ligaments. Dorsally, the opening of the rings is completed by the trachealis muscle and the dorsal tracheal ligament (or tracheal membrane). The inner wall of the trachea is lined with a mucous membrane composed of pseudostratified ciliated columnar epithelium containing goblet cells (mucus-producing cells).

The arrangement of the tracheal rings and the trachealis muscle varies among species:

• Dog and Cat (Carnivores): In carnivores, the trachea is composed of 35 to 46 C-shaped cartilaginous rings. The dorsal ends of the rings do not meet, and the space is filled by the tracheal membrane and the trachealis muscle.

• Ruminants (Cattle, Sheep): In cattle and sheep, the ends of the tracheal rings meet dorsally to form a ridge, leaving only a small opening filled by the membrane and the trachealis muscle.

• Horse: In horses, the ends of the tracheal rings overlap dorsally.

The structure of the human trachea is very similar to that of certain animals, particularly the goat, which is considered the ideal animal model for tracheal surgery due to this resemblance. As in dogs and goats, human cartilaginous rings are dorsally incomplete, and their ends do not meet. This dorsal space is filled by a fibroelastic membrane and the trachealis muscle. This configuration differs from that observed in horses (where the rings overlap) or in ruminants (where the rings almost completely meet).