Difference Between Terminal and Respiratory Bronchioles

The key difference between terminal and respiratory bronchioles is that terminal bronchioles are the last component of conducting division of the respiratory tract while respiratory bronchioles mark the beginning of the respiratory division.

The respiratory system consists of different parts such as nasal cavity, nasopharynx, larynx, trachea, bronchi and bronchioles. There are two major divisions of the respiratory system. They are conducting zone and respiratory zone. Conducting zone facilitates the transportation of gases while the respiratory zone facilitates the exchange of gases.  Parts of the conducting zone are nose, pharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles. Parts of the respiratory zone are respiratory bronchioles, alveolar ducts and alveoli. Terminal bronchioles are the last part of the conducting division, while respiratory bronchioles are the beginning of the respiratory division. Therefore, terminal bronchioles mark the end of conducting zone while respiratory bronchioles mark the beginning of the respiratory zone. Terminal bronchioles give rise to respiratory bronchioles.

CONTENTS

1. Overview and Key Difference
2. What are Terminal Bronchioles
3. What are Respiratory Bronchioles
4. Similarities Between Terminal and Respiratory Bronchioles
5. Side by Side Comparison – Terminal vs Respiratory Bronchioles in Tabular Form
6. Summary

What are Terminal Bronchioles?

Terminal bronchioles are the final branches of the conducting division of the respiratory tract. In other words, terminal bronchioles are the last component of the conducting zone of the respiratory system. They are the smallest conducting airways in the respiratory tract. Bronchioles become smaller and divide into thin-walled terminal bronchioles. The epithelium of terminal bronchioles consists of simple columnar ciliated cells. Terminal bronchioles then give rise to respiratory bronchioles.

The diameter of terminal bronchioles is less than 1 mm. Moreover, they do not possess cartilage. They also do not have alveoli in their walls. In each lung, there are about 30,000 terminal bronchioles. The major function of the terminal bronchioles is the conduction of gases in and out of the lungs. In addition, terminal bronchioles offer a low resistance pathway for airflow. Moreover, they provide a defence role as well by filtering the air.

What are Respiratory Bronchioles?

Respiratory bronchioles are the narrowest airways that mark the beginning of the respiratory zone of the respiratory system. Terminal bronchioles divide and give rise to respiratory bronchioles. However, unlike terminal bronchioles, respiratory bronchioles have alveoli along their walls.

Respiratory bronchioles split into a number of alveolar ducts. Respiratory bronchioles are lined by the ciliated cuboidal epithelium and some non-ciliated Clara cells. The walls of respiratory bronchioles are discontinuous, having openings to alveolar ducts. Respiratory bronchioles facilitate gas exchange by delivering air to the exchange surfaces of the lungs.

What are the Similarities Between Terminal and Respiratory Bronchioles?

• Terminal and respiratory bronchioles are two parts of the respiratory system.
• Terminal bronchioles divide to form respiratory bronchioles.
• Both terminal and respiratory bronchioles are airways.
• They are lined by an epithelium.

What is the Difference Between Terminal and Respiratory Bronchioles?

Terminal bronchioles are the smallest conducting airways of the respiratory system, while respiratory bronchioles are the narrowest airways of the respiratory system. Furthermore, the terminal bronchioles mark the end of conducting zone of the respiratory system while the respiratory bronchioles mark the beginning of the respiratory zone of the respiratory system. So, we can consider this as the key difference between terminal and respiratory bronchioles.

Moreover, terminal bronchioles do not have alveoli in their walls while respiratory bronchioles have alveoli along their walls. Also, functionally, terminal bronchioles facilitate the conduction of air in and out of the lungs while respiratory bronchioles facilitate the exchange of air.

The below info-graphic lists more differences between terminal and respiratory bronchioles in tabular form.

Summary – Terminal vs Respiratory Bronchioles

Terminal and respiratory bronchioles are two types of airways found in the respiratory system. Terminal bronchioles belong to the conducting zone of the respiratory system, while respiratory bronchioles belong to the respiratory zone. Terminal bronchioles conduct air in and out of the lungs while respiratory bronchioles facilitate the exchanging of air. Moreover, the diameter of terminal bronchioles is less than 1 mm while the diameter of respiratory bronchioles is about 0.5 mm. Also, terminal bronchioles do not have alveoli in their walls while respiratory bronchioles have alveoli along their walls.  In addition to these, the terminal bronchioles split into respiratory bronchioles while the respiratory bronchioles split into alveolar ducts. This summarizes the difference between terminal and respiratory bronchioles.

Reference:

1. “Bronchiole.” Wikipedia, Wikimedia Foundation, 15 Dec. 2020, Available here.
2. Cianciolo, Rachel, et al. “Air Conduction: Terminal Bronchioles, Respiratory Bronchioles and Alveolar Ducts.” Veterinary Histology, The Ohio State University, 22 Aug. 2017, Available here.

Image Courtesy:

1. “Secondary-pulmonary-lobule-illustration” By Frank Gaillard – Case courtesy of A.Prof Frank Gaillard, from Radiopaedia (CC BY-SA 4.0) via Commons Wikimedia
2. “2309 The Respiratory Zone” By OpenStax College – Anatomy & Physiology, Connexions Web site, Jun 19, 2013 (CC BY 3.0) via Commons Wikimedia