What is a Bronchus?

Dorothy Distefano

A bronchus is one of the large tubes that lead from the human trachea to the lungs. There is one large bronchus in each lung that branches out into smaller bronchi within the lungs. Bronchi carry air into and out of the lungs.

Asthma occurs when a bronchus is obstructed.
Asthma occurs when a bronchus is obstructed.

The respiratory system begins at the nose and mouth, which meet at the pharynx. At the bottom of the pharynx are the esophagus, for food, and the trachea, for air. The epiglottis is a flap of tissue that covers the trachea when swallowing, to prevent food from passing into the airway as it enters the esophagus.

Bronchitis is an inflammation of the bronchial airways.
Bronchitis is an inflammation of the bronchial airways.

At the top of the trachea is the larynx. This is the home of the vocal cords, which vibrate to create speech and sounds. The trachea continues beyond the neck and into the chest cavity, where it divides into the bronchi. The bronchi extend into the lungs.

The right main bronchus is larger than the left. It divides into three lobar bronchi. The left main bronchus splits off into two lobar bronchi. The lobar bronchi then branch into what are called tertiary bronchi, and then into smaller bronchioles.

The bronchioles eventually branch into alveolar ducts and sacs. The alveoli, or air sacs, are the primary units for the exchange of oxygen and carbon dioxide in the lungs. A human has approximately 480 million alveoli.

The muscle that separates the chest from the abdomen is the diaphragm. This is the main muscle used in respiration. Inhalation occurs when the diaphragm contracts and moves downward. The air pressure within the chest cavity is reduced, causing air to flow into the lungs. In exhalation, the diaphragm is relaxed and pushes air out of the chest.

Asthma is a disorder in which the bronchi are obstructed, often causing wheezing and difficult or painful breathing. Treatment may include inhaled corticosteroids to decrease inflammation, as well as bronchodilators to keep airways open. There is no cure for asthma and treatment is based on controlling symptoms.

Bronchospasm is the contraction of the smooth muscle in a bronchus or bronchiole. This condition may be caused by irritation or injury to the mucosa in the airway, by infection, or due to allergy. Symptoms include a severe cough and wheezing. Treatment is similar to that for asthma.

Bronchitis is an inflammation of the bronchial airways related to infection, allergies, or other causes. When the lining of the bronchi become inflamed, they swell and create excessive secretions. Antibiotics, cool-mist vaporizers, and fluids can all be included in its treatment.

A bronchus is one of the large tubes that lead from the trachea to the lungs.
A bronchus is one of the large tubes that lead from the trachea to the lungs.

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Discussion Comments


I had pneumonia once. Besides just being tired, and running a fever, and coughing all the time, my lungs felt terrible. I think with pneumonia, an infection drops down into the lungs and those alvioli become infected and clogged with mucus so you have trouble breathing and cough like crazy to try to get the mucus out.

It took me almost three weeks to get over it, while taking antibiotics. I got it after having the flu. The next year, I got a pneumonia shot so I shouldn't ever get it again.


@cardsfan27 - From what I understand about asthma, they don't know exactly what causes it. People with asthma always have airways that are inflamed and sometimes constricted. When something triggers the asthma reaction, like allergies, cold or flu infection, cold weather, too much exercise or other things, then the airways to the lungs tighten and become more inflamed. The person may have difficulty breathing.

Breathing in a chemical solution that is heated by a machine helps the patient to breath easier. If it is a serious attack, a trip to the ER might be necessary.


@jmc88 - For your first question, the right bronchus is split into three parts because the right lung is in three sections compared to two section in the left lung. I don't think I have ever heard a really good explanation for why that is the case, but it is.

As for the second question about pneumonia, I think you make a good point. I don't know the answer, but it does seem like I have heard of people having bronchitis that progressed into pneumonia, which is more serious. The article talks about it making secretions. Maybe that has something to do with it.

Besides just being a transportation tube for air, are there any more bronchus functions? I know for a lot of the trip air takes into the lungs, there are hairs and other things that stop foreign particles from making it into the lungs. Do the bronchi have anything like that?


Why would the right bronchus be split into more branches than the left one? That doesn't seem like it makes a lot of sense.

I was also wondering if pneumonia was related to bronchitis or some other problem with the bronchi. I know pneumonia is technically something to do with having an inflamed lung, but it seems like I have heard of people having pneumonia, and it started out as bronchitis. The article says that bronchitis can be an infection, so maybe pneumonia is just when the bacteria or virus or whatever it is makes it way into the lungs. Does anyone here know?


@cardsfan27 - I think you're right that asthma is caused by some chemical reaction when certain irritants get into the bronchi. That in itself doesn't really surprise me, but what I would really be interested to know is why it only happens to some people.

I think it is interesting, too, that you mentioned pollen which is usually thought of as causing allergies, but I am pretty sure that a lot of people with asthma also are more likely to have allergies. I am not sure why that is, either.

I know a few people with asthma who are able to play sports just fine. They might start having problems after they have been running a long time, but the inhaler usually fixes it. I guess it just depends on the severity of your asthma, but I know some people that could play entire basketball games without any problems.


Does anyone know, what exactly is it that causes asthma? Luckily, I don't have it, but I know a few people that do. I know different things can cause the asthma to act up. Do things like pollen get into the bronchi and cause them to swell up, or is it some type of reaction in them? Why is it only certain things that cause asthma symptoms to start?

I know some people with asthma have a hard time running long distances. Is that related, too?

On the same topic, what is in asthma inhalers that makes people be able to breathe better? Obviously, it is some type of chemical, but what does it do in the bronchi?

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