Difference Between Bronchi and Bronchioles

Main Difference – Bronchi vs Bronchioles

Mammals breathe through lungs. The respiratory system of mammals is composed of the nose, mouth, larynx, trachea, bronchi, bronchioles, and alveoli. Both bronchi and bronchioles are tubular structures. Bronchi consist of C-shape cartilages while bronchioles lack cartilaginous support. The diameter of bronchi is higher than that of the bronchioles as bronchi occur at the front of the respiratory passageway. Bronchi emerge from the trachea and branch to form bronchioles that are connected to the alveoli. The main difference between bronchi and bronchioles is that bronchi are involved in the conducting, warming, and cleaning the air in the respiratory passageway whereas bronchioles are involved in the conduction of air as well as gas exchange.

Key Areas Covered

1. What are Bronchi
     – Definition, Structure, Function
2. What are Bronchioles
     – Definition, Structure, Function
3. What are the Similarities Between Bronchi and Bronchioles
     – Outline of Common Features
4. What is the Difference Between Bronchi and Bronchioles
   – Comparison of Key Differences

Key Terms: Bronchi, Bronchioles, Cartilages, Gas Exchange, Lobular Bronchioles, Primary Bronchi, Respiratory Bronchioles, Secondary Bronchi, Terminal Bronchioles, Tertiary Bronchi

Difference Between Bronchi and Bronchioles - Comparison Summary

What are Bronchi

Bronchi refer to the tubules that form the main passageway of air into the lungs. The air travels from nose to the larynx and trachea. Trachea conducts air to bronchi. Three types of bronchi can be identified based on the branching pattern; primary bronchi, secondary bronchi, and tertiary bronchi. Bronchi become smaller in diameter when they come from primary to tertiary bronchi. Primary bronchi occur at the separating point of the trachea into left and right bronchus. Secondary bronchi occur in the middle of the lungs. Tertiary bronchi occur near the bottom of the lungs, just above the bronchioles. The structure of the bronchi in the respiratory pathway is shown in figure 1.

Difference Between Bronchi and Bronchioles

Figure 1: Bronchi

The primary function of bronchi is to conduct air to the bottom of the lungs. The wall of the bronchi is made up of a fibrocartilage layer. This layer prevents the shrinking of the bronchi tube during breathing. During the conduction, air is warmed and cleaned. Ciliated pseudostratified epithelium makes the lining of the bronchi. It consists of mucus-secreting goblet cells. The mucus traps dust and pathogens, and the action of cilia eliminates the dust from the respiratory passageway. However, no gas exchange occurs through the wall of bronchi. The swollen bronchi due to infections cause bronchitis, making breathing difficult. Excess mucus and phlegm may also cause bronchitis.

What are Bronchioles

Bronchioles refer to the minus branches that form alveoli. Each lung consists of around 30,000 bronchioles. They are not encircled with cartilages. Bronchioles are made up of smooth muscles, elastic connective tissue, and simple cuboidal epithelium with goblet cells. Three parts can be identified in bronchiole based on the branching pattern. They are lobular bronchioles, terminal bronchioles, and respiratory bronchioles. Lobular bronchioles are also called preterminal bronchioles. They branch to form terminal bronchioles after passing into a pulmonary lobule. Terminal bronchioles are composed of simple cuboidal epithelium but, it lacks goblet cells. They develop the respiratory bronchioles, capable of gas exchange. They are made up of non-ciliated cells and lead to alveoli. The structure of bronchioles and alveoli are shown in figure 2.

Main Difference - Bronchi vs Bronchioles

Figure 2: Bronchiole and Alveoli

The two major functions of the bronchioles are the conduction of air to alveoli and gas exchange. Bronchitis, bronchiectasis (permanent damage and dilation of bronchioles), bronchospasm (sudden constriction of bronchioles walls), and emphysema (chronic obstructive pulmonary disease – COPD) are the possible clinical conditions in bronchioles.

Similarities Between Bronchi and Bronchioles

  • Bronchi and bronchioles are two types of tubular structures that occur before the alveoli in the respiratory passageway.
  • The epithelium of both bronchi and bronchioles are composed of cilia.
  • The epithelium of both bronchi and bronchioles consist of goblet cells that produce mucus.

Difference Between Bronchi and Bronchioles

Definition

Bronchi: Bronchi refer to the tubules that form the main passageway of air into the lungs.

Bronchioles: Bronchioles refer to the minus branches that form alveoli.

Formation

Bronchi: Bronchi are formed from the primary bronchi.

Bronchioles: Bronchioles are formed from bronchioles.

Form

Bronchi: Bronchi form bronchioles.

Bronchioles: Bronchioles form alveoli.

Structure

Bronchi: Bronchi are made up of a fibrocartilaginous layer.

Bronchioles: Bronchioles are made up of smooth muscles, elastic tissues, and epithelium.

Sections

Bronchi: Bronchi can be divided into three sections: primary bronchi, secondary bronchi, and tertiary bronchi.

Bronchioles: Bronchioles can be divided into three sections: lobular bronchioles, terminal bronchioles, and respiratory bronchioles.

Cartilages

Bronchi: Bronchi consist of C-shape cartilages rings that provide support.

Bronchioles: Bronchioles lack cartilaginous support.

Type of Epithelium

Bronchi: Bronchi are made up of the pseudostratified columnar epithelium.

Bronchioles: Bronchioles are made up of simple cuboidal epithelium, which is ciliated.

Diameter

Bronchi: The diameter of bronchi is high.

Bronchioles: The diameter of bronchioles is less than that of bronchi.

Function

Bronchi: Conducting, warming, and cleaning the air in the respiratory passageway are the major functions of bronchi.

Bronchioles: Conduction, as well as the gas exchange, are the main functions of bronchioles.

Conduction of Air

Bronchi: Bronchi conduct air to bronchioles.

Bronchioles: Bronchioles conduct air to alveoli.

Pathology

Bronchi: Bronchitis is a possible clinical condition in bronchi.

Bronchioles: Bronchitis, bronchiectasis, bronchospasm, and emphysema are the possible clinical conditions in bronchioles.

Conclusion

Bronchi and bronchioles are two types of tubules that occur in the respiratory passageway of the lungs. Bronchi occur before the bronchioles and bronchioles give rise to alveoli. Bronchi are surrounded by cartilaginous layer. Bronchi are involved in the conduction of air to the bottom part of the respiratory passageway. Bronchioles conduct air, and they are also involved in the gas exchange as alveoli. The main difference between bronchi and bronchioles is their structure and function.

Reference:

1. “Bronchi Function, Definition & Anatomy | Body Maps.” Healthline, Healthline Media, Available here.
2. “Bronchioles.” The Respiratory System, Available here.

Image Courtesy:

1. “Alveoli diagram” By The original uploader was Pdefer at English Wikipedia – Transferred from en.wikipedia to Commons by Smooth_O using CommonsHelper. (CC BY-SA 3.0) via Commons Wikimedia
2. “Figure 39 01 07” By CNX OpenStax(CC BY 4.0) via Commons Wikimedia

About the Author: Lakna

Lakna, a graduate in Molecular Biology & Biochemistry, is a Molecular Biologist and has a broad and keen interest in the discovery of nature related things

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