Anatomy, Histology, and Cytology of Normal Components of the Lower Respiratory Tract

Abstract

The lungs are paired intrathoracic organs derived from the primitive foregut as ventral buds, extending into the primitive thoracic mesenchyme. The bronchial cartilage, smooth muscle, and other connective tissues are derived from this mesenchyme. The lungs are divided into lobes by fissures. The right lung has three lobes (i.e., upper, middle, and lower), whereas the left lung has two lobes (i.e., upper and lower). The lingula, a portion of the superior segment of the upper lobe, represents the middle lobe for the left lung. Each lobe is further divided into bronchopulmonary segments. The segmental lung anatomy is important in precisely designating tumor location.