Difference Between Trachea and Bronchi

The main difference between trachea and bronchi is that the trachea is the airway that connects the larynx to the bronchi whereas the bronchi are the two branching airways that lead to the lungs. Furthermore, the trachea is a thin-walled tube while bronchi is a thick-walled tube.  

Trachea and bronchi are the two type of airways that lead to the lungs. Lungs are the organs involved in the exchange of respiratory gases in higher animals. Both trachea and bronchi consist of respiratory mucosa with mucus-secreting cells. 

Key Areas Covered 

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

Key Terms 

Bronchi, Cartilaginous Rings, Conduct Air, Trachea

What is Trachea 

Trachea or the windpipe is the main airway of the respiratory system, which connects the larynx to the bronchi. It starts under the larynx and runs under the sternum, and divides into two bronchi at the level of T4-5 vertebrae. The length of the trachea is around 4 inches. The diameter of the lumen is around 1 inch. Its cross section holds a D-shape due to the presence of incomplete or C-shaped cartilaginous rings only interiorly and laterally along the trachea. The posterior wall of the trachea does not contain these rings. Around 15-20 rings occur along the trachea, and they are made up of hyaline cartilage. The main function of these rings is to prevent the collapse of the membranous tube during inhalation. At the bottom of the trachea, carina, which is a knee-like partition separates the main tube into two bronchi. 

Figure 1: Trachea

The four tissue layers that make up the wall of the trachea are respiratory mucosa or the mucous membrane, submucosa, tracheal muscles, and adventitia.  

• Respiratory mucosa – Made up of pseudostratified ciliated columnar epithelium, which contains mucus-producing goblet cells. It warms, moistens and cleans the air that enters the trachea. 
• Submucosa – Made up of loose connective tissue. It contains blood vessels, neurons, and seromucous glands, which produce and secrete a mixture of water and mucus. Cartilaginous layer occurs external to the submucosa. 
• Trachealis muscles – Open ends are attached to the cartilaginous rings. They contract while coughing.  
• Adventitia – A band made up of loose connective tissue. It binds the trachea to the esophagus.  

What are Bronchi 

Bronchi are the airways that connect the trachea to each lung. They also contain the cartilaginous thickening with the hyaline cartilage. Each bronchus branches further while reaching to the lungs. Therefore, based on this branching pattern, bronchi are classified into three levels: primary bronchi, secondary bronchi, and tertiary bronchi.  

• Primary bronchi – The two main bronchi which connect the trachea to the bottom bronchi. They are called left and right bronchi according to the corresponding lungs to which they supply the air. 
• Secondary bronchi – They occur in the middle of the lungs, carrying air from primary bronchi to the bottom. They conduct air to each of the five lobes of the lungs, and due to their location at the level of lobes, secondary bronchi are called lobar bronchi.  
• Tertiary bronchi – The deepest bronchi in the lungs, which form bronchioles from their ends.  
  

  Figure 2: Bronchi Classification

The anatomy of the primary bronchi is more similar to that of the trachea, and they contain C-shaped rings. However, the amount of hyaline cartilage decreases with the branching and bronchioles do not contain cartilage at all. But, the amount of smooth muscles increases with the decreasing cartilage. The mucous membrane also shifts into simple cuboidal and simple squamous epithelium. Infections cause swollen bronchi, which makes difficulties in breathing. This situation is called bronchitis. 

Similarities Between Trachea and Bronchi 

• Trachea and bronchi are the airways which lead to the lungs. 
• Their main function is to conduct air to the lungs while warming, moistening, and cleaning it. 
• They possess cartilaginous plates made up of hyaline cartilage for the support. The lumen is D-shaped in both.  
• Both have respiratory mucosa lining, which produces mucus. 
• No gas exchange occurs through the tracheal or bronchial walls. 

Difference Between Trachea and Bronchi 

Definition 

Trachea refers to the windpipe, which is a large membranous tube reinforced by rings of cartilage, extending from the larynx to the bronchial tubes and conveying air to and from the lungs while bronchi refer to any of the major air passages of the lungs which diverge from the windpipe.  

Correspondence 

The trachea is the airways which connect the larynx to the bronchi while bronchi are the airways which connect the trachea to the lungs. 

Number 

There is only one trachea in the respiratory system while two bronchi occur in the respiratory system, which branches further. 

Thickness of the Wall 

The wall of the trachea is thin while the walls of bronchi are comparatively thick due to increasing amounts of smooth muscles. 

Cartilage 

Trachea contains C-shaped cartilaginous rings while smaller bronchi contain irregularly arranged plates and islands. 

Conclusion 

The trachea is the main airway which connects the larynx to the bronchi while the bronchi are the branching airways which conduct air into the lungs. Both contain cartilaginous support. The main difference between trachea and bronchi is their location and function. 

Reference:

1. “Tracheal Wall Composition and Structure – Anatomy of the Tracheal Tube or Windpipe.” GetBodySmart, 16 Nov. 2017, Available Here
2. “Bronchial Tubes Structure, Functions, & Location | Bronchus Anatomy.” GetBodySmart, 16 Nov. 2017, Available Here

Image Courtesy:

1. “Blausen 0865 TracheaAnatomy” By BruceBlaus. Blausen.com staff (2014). “Medical gallery of Blausen Medical 2014”. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436. – Own work (CC BY 3.0) via Commons Wikimedia
2. “Figure 39 01 07” By CNX OpenStax – (CC BY 4.0) via Commons Wikimedia