Anatomy and Physiology of Children and Adolescents - M. R. Sapin 2007

The Doctrine of Viscera (Splanchnology)
Respiratory System
Trachea and Bronchi

The Trachea extends from the lower border of the sixth cervical vertebra to the upper border of the fifth thoracic vertebra. Superiorly, the trachea is connected to the Larynx by ligaments; inferiorly, it bifurcates into two main Bronchi: the right and the left.

The framework of the trachea consists of 16–20 cartilaginous semirings that are open posteriorly and connected to one another by short annular ligaments. The posterior wall of the trachea, which is adjacent to the Esophagus and lacks Cartilage, is membranous. It is composed of Connective Tissue and smooth Muscle bundles. The mucous membrane of the trachea is lined with ciliated epithelium and contains numerous glands and lymphoid nodules.

At the level of the fifth thoracic vertebra, the trachea divides into the right and left main bronchi (the tracheal bifurcation), with each passing toward the hilum of the lung. The right main bronchus is shorter and wider than the left; it appears almost as a direct continuation of the trachea and enters the hilum of the right lung. The longer left main bronchus diverges at a sharper angle to the left and enters the hilum of the left lung. The walls of the main bronchi share the same histological Structure as the tracheal wall. The framework of the main bronchi is formed by cartilaginous semirings. Within the hila of the Lungs, the main bronchi divide into lobar bronchi: the right lung has three lobar bronchi, while the left has two. The lobar bronchi further divide into segmental and smaller bronchi, forming 22–23 orders of branching within each lung. This ramification of the bronchi within the lung is known as the bronchial tree. As the diameter of the bronchi decreases, the hyaline cartilage in their walls is gradually replaced by elastic cartilage plates. In smaller bronchi, cartilage tissue is absent altogether, and the Cytology/cytology/32.html">Smooth Muscle tissue becomes prominently developed.



Last update: 10/08/2026

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