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Function of the Respiratory Bronchioles

Amanda Robb, Nicholas Gauthier
  • Author
    Amanda Robb

    Amanda has taught high school science for over 10 years. She has a Master's Degree in Cellular and Molecular Physiology from Tufts Medical School and a Master's of Teaching from Simmons College. She is also certified in secondary special education, biology, and physics in Massachusetts.

  • Instructor
    Nicholas Gauthier

    Nicholas has a B.A. in Biology and Master of Secondary Education in Biology. He has New York State Permanent Certification in Biology, Earth Science, and General Science. He has over thirteen years of teaching experience. Prior to teaching, he gained hands on experience working in various medical labs.

Learn about the definition of respiratory bronchioles, the plural of bronchiolus. Discover the bronchioles' function, and study the relationship between bronchi and bronchioles and the relationship between bronchioles and alveoli. Updated: 09/27/2021

What are Bronchioles?

Breathing in and out is something we often take for granted, until our breathing is compromised. Plenty of respiratory infections can cause difficulty breathing. Many affect a part of the lungs called the bronchioles. Bronchioles, singular form is bronchiolus, are small tubes within the lungs that bring air in for gas exchange.

Structure of a Bronciolus

The structure of a bronchiolus is a thin tube. The tubes are anchored into the lung tissue with the protein elastin, which also allows for expansion of the bronchioles. The inner lining of the bronchioles is called the lamina propria, which is surrounded by a layer of smooth muscle. The smooth muscle is able to expand and contract, providing constriction and expansion of the bronchioles. The bronchioles are thus flexible and do not contain the hyaline cartilage found in other parts of the airway.

The bronchioles also contain club cells that secrete surfactant. Surfactant helps reduce the surface tension within the bronchioles and prevents them from collapsing.

Lastly, extending from the lamina propria are small, hair like projections called cilia. Cilia help to remove pathogens, dust and other antigens that enter the lungs. The cilia beat upward and move mucus with the contaminants out of the lungs and into the digestive system for elimination.

What are Bronchioles?

The respiratory system consists of a pair of lungs and a trachea through which we draw in air. Air pressure of the atmosphere forces the air inside. For this to happen, the body must lower air pressure inside the chest cavity. It does this by expanding the cavity, using muscles in the rib cage and a special muscle called a diaphragm located under the lungs.

When we breathe, the air is first drawn in through the mouth and nose. Moving downward, it goes through the pharynx (or the throat) and through the larynx (or the voice box). From there, it enters the main airway called the trachea. The trachea has rings of cartilage supporting it. The trachea branches off into two bronchi, one for each lung.

The bronchi themselves branch several times into smaller divisions. After several branches, these airways are no longer supported by rings of cartilage, and are called bronchioles.

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The Breathing Process

During breathing, air enters the nose and mouth and moves through the trachea. As we inhale muscles below the lungs called the diaphragm in conjunction with the rib muscles expand the lungs. This creates negative pressure that pulls air in through the airways. As air comes in through the trachea it moves through the right and left bronchi to the bronchioles. The bronchioles expand to accommodate the airflow and dead end in the alveoli. In the alveoli oxygen diffuses from the lungs into the blood. Carbon dioxide and water vapor are released from the blood into the lungs and are exhaled. The millions of alveoli clusters at the end of the bronchioles allow for a large surface air for gas exchange to occur over.

Bronchioles Function: What Do Bronchioles Do?

The function of the bronchioles is to bring air to each alveolar cluster. The bronchioles allow for air to access deeper parts of the lungs and ultimately brings air to the alveolar clusters where gas exchange can occur. The branching structure of the bronchioles and alveoli create a large surface area to allow for the most efficient method of gas exchange.

Bronchi and Bronchioles

The bronchi and bronchioles are related structures in the lungs. The bronchi are two large branches that extend from the trachea into the right and left lung. The bronchi are firm and have complete rings of cartilage, similar to the trachea. The main bronchi branch as they enter each lung into the lobular bronchi and finally the segmental bronchi. The segmental bronchi branch into the smaller tubes of the bronchioles.

Bronchioles and Alveoli

The bronchioles are also related to the alveoli. Alveoli are small, circular structures that form clusters at the end of the bronchioles. The main function of the alveoli is to facilitate gas exchange with the blood vessels of the circulatory system. The alveoli are made of a single cell layer thick to facilitate diffusion. There are millions of alveoli and this allows for a large surface area to facilitate gas exchange. The bronchioles are the tiny tubes that bring air to the alveoli.

Types of Bronchioles

There are three types of bronchioles in the lungs, including:

  • Lobular bronchioles
  • Respiratory bronchioles
  • Terminal bronchioles

Each type is described in more detail in the following sections.

Lobular Bronchioles

The lobular bronchioles are the largest bronchioles and are the first branch from the bronchi and enter the lobes of the lungs. They are differentiated from other bronchiole types by their size, as lobular bronchioles are the largest of the three types of bronchioles.

Function

The lungs are filled with millions of microscopic alveoli to allow for a high rate of exchange of gases with the atmosphere. Each air sac provides surface area for this gas exchange. In order to get air to all of the alveoli, the bronchioles have to branch smaller and smaller. Bronchioles range in diameter from several millimeters to less than half a millimeter. The tip of each bronchiole, called a terminal bronchiole, ends at a cluster of alveoli that it feeds. The function of the bronchioles is to ensure that incoming air is supplied to each alveolus.

The alveoli are surrounded by tiny blood vessels called capillaries. It is through the thin capillary walls that oxygen enters the blood, and carbon dioxide and water leave the blood. The carbon dioxide and water vapor are then expelled from the lungs via the trachea, and into the air.

Oxygen is used for cellular respiration, which is when our cells break down simple molecules, like glucose, into energy compounds. Water and carbon dioxide are waste products of cellular respiration. Other atmospheric gases, such as nitrogen, also enter and leave the bloodstream, but the levels stay relatively constant since our bodies do not use or produce them.

The trachea, bronchi and larger bronchioles have an inner lining of mucus that traps antigens, such as dust and invading microorganisms. Hair-like structures, called cilia, move this mucus along toward the throat, where we cough to remove it from our lungs. It tends to go down into the esophagus where it is swallowed, though strong coughing can expel this mucus from the mouth and into the air.

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Video Transcript

What are Bronchioles?

The respiratory system consists of a pair of lungs and a trachea through which we draw in air. Air pressure of the atmosphere forces the air inside. For this to happen, the body must lower air pressure inside the chest cavity. It does this by expanding the cavity, using muscles in the rib cage and a special muscle called a diaphragm located under the lungs.

When we breathe, the air is first drawn in through the mouth and nose. Moving downward, it goes through the pharynx (or the throat) and through the larynx (or the voice box). From there, it enters the main airway called the trachea. The trachea has rings of cartilage supporting it. The trachea branches off into two bronchi, one for each lung.

The bronchi themselves branch several times into smaller divisions. After several branches, these airways are no longer supported by rings of cartilage, and are called bronchioles.

Function

The lungs are filled with millions of microscopic alveoli to allow for a high rate of exchange of gases with the atmosphere. Each air sac provides surface area for this gas exchange. In order to get air to all of the alveoli, the bronchioles have to branch smaller and smaller. Bronchioles range in diameter from several millimeters to less than half a millimeter. The tip of each bronchiole, called a terminal bronchiole, ends at a cluster of alveoli that it feeds. The function of the bronchioles is to ensure that incoming air is supplied to each alveolus.

The alveoli are surrounded by tiny blood vessels called capillaries. It is through the thin capillary walls that oxygen enters the blood, and carbon dioxide and water leave the blood. The carbon dioxide and water vapor are then expelled from the lungs via the trachea, and into the air.

Oxygen is used for cellular respiration, which is when our cells break down simple molecules, like glucose, into energy compounds. Water and carbon dioxide are waste products of cellular respiration. Other atmospheric gases, such as nitrogen, also enter and leave the bloodstream, but the levels stay relatively constant since our bodies do not use or produce them.

The trachea, bronchi and larger bronchioles have an inner lining of mucus that traps antigens, such as dust and invading microorganisms. Hair-like structures, called cilia, move this mucus along toward the throat, where we cough to remove it from our lungs. It tends to go down into the esophagus where it is swallowed, though strong coughing can expel this mucus from the mouth and into the air.

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Frequently Asked Questions

What is the function of respiratory bronchioles?

The function of the respiratory bronchioles is to bring air to the alveolar clusters for gas exchange. Gas exchange involves taking in oxygen and releasing carbon dioxide.

What is the difference between bronchi and bronchioles?

Bronchi are larger tubes in the lungs that branch from the trachea. They deliver air to the bronchioles. The bronchioles are smaller tubes that branch from the bronchi and bring air to the alveoli.

Is there gas exchange in respiratory bronchioles?

There is no gas exchange in the respiratory bronchioles. Gas exchange is the process of bringing oxygen into the blood and releasing carbon dioxide. This process takes place in the alveoli.

What are respiratory bronchioles made of?

Respiratory bronchioles are made of cells. They have an inner lining made of epithelial cells and mucus secreting cells. This layer is surrounded by smooth muscle cells that control the dilation of the bronchioles. The bronchioles are attached to the rest of the lung with connective tissue such as collagen proteins.

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