What is not found in the terminal bronchioles?

• A. Cartilage
• B. Bronchiolar smooth muscle
• C. Goblet cells
• D. Pseudostratified ciliated columnar epithelium

Answer: (A)

The terminal bronchioles do not contain cartilage, which is a defining feature of their structure. As the airways transition from larger bronchi to smaller bronchioles, the amount of cartilage progressively decreases. By the time the airways reach the terminal bronchioles, there is a complete absence of cartilage, allowing for more flexibility and compliance in this region, which is particularly important for airflow regulation and accommodating the dynamics of breathing.

In contrast, terminal bronchioles are characterized by the presence of bronchiolar smooth muscle, which facilitates the constriction and dilation necessary for regulating airflow resistance. Goblet cells, though decreased in number compared to larger airways, are still present, contributing to the secretion of mucus that helps trap debris and pathogens. Furthermore, the epithelium in terminal bronchioles is composed of simple cuboidal cells rather than pseudostratified ciliated columnar epithelium, which is typical of larger bronchi. The loss of ciliated cells and the presence of secretory cells in the terminal zone support the role of terminal bronchioles in final conditioning of inspired air before it reaches the alveoli.