Bronchi are the main airways into the lungs. Bronchi is the plural form of bronchus.

Air enters your body through your mouth or nose and it passes through the larynx and trachea. The trachea, also called the windpipe, branches into a bronchus in each lung.

The bronchi then branch out again and become smaller and smaller passageways until they end in tiny air sacs called alveoli. Alveoli perform the important work of adding oxygen back into your blood and removing carbon dioxide.

The structure of the trachea and the bronchi together are called the tracheobronchial tree, or more simply, the bronchial tree. Together, they look a lot like an upside down tree: the trachea forms the trunk and the bronchi form the branches of all sizes.

Bronchi branch out throughout both lungs. The right lung, which has one additional lobe, has more bronchi than the left lung.

Healthy bronchi keep you breathing as expected. If bronchi become infected or inflamed, you may experience difficulties with breathing, mucus buildup, or other issues.

When you take a breath through your nose or mouth, air travels into the larynx. Then, the air passes through the trachea, which carries the air to the left and right main bronchus.

The main bronchi branch out and become narrower the closer they get to the lung tissue.

The smallest bronchi branches are called bronchioles. These passageways evolve into alveoli, which is the site of oxygen and carbon dioxide exchange in the respiratory system. No gas exchanges occur in any of the bronchi.

Beyond moving air throughout your lungs, the bronchi are responsible for protecting your lungs from possible infection or injury. Mucus cells lining the bronchi moisturize the air as it enters your lungs. The mucus can capture foreign particles, including:

  • viruses
  • bacteria
  • fungi
  • bits of dust and debris

Bronchi are also lined with tiny hair-like structures called cilia. The cilia help move mucus, or phlegm, out of your lungs. They push out any captured particles, which helps keep your bronchi clean and healthy.

How do your bronchi work with your respiratory system?

The bronchi carry air in and out of the lungs.

Oxygen-rich air is exchanged for carbon dioxide in the alveoli. To get that carbon dioxide out of your body, air is pushed out of the bronchi, up the trachea, and out of your mouth or nose. This occurs during an exhale.

The bronchi may just be passageways for air, but they’re very important to the full and healthy functioning of your respiratory system.

The bronchi are divided into different sections, and each section changes as it branches into smaller and smaller airways.

The parts of the bronchi are:

  • Primary bronchi. The largest and widest parts of the bronchi are located in the upper part of the lungs. Due to the shape and size of the lungs, the right primary bronchi is shorter than the left, and the left primary bronchi is narrower than the right.
  • Secondary bronchi. Also called lobar bronchi, the secondary bronchi are located near the middle of the lungs. There is one secondary branch per lobe of the lung. The right lung has three secondary bronchi, and the left lung has two.
  • Tertiary bronchi. These smaller bronchi, also called segmental bronchi, are located near the bottom of the bronchi, just before it turns into the narrowest passageways.
  • Bronchioles. These are the narrowest airways of the bronchial tree. At the end of bronchioles are alveoli, the small sacs that do the work of exchanging gases.

Bronchi are made up of a combination of cartilage and tissue. The cartilage keeps the bronchi strong and open as air travels through with each inhale and exhale.

As the airways get smaller and smaller, the ratio of cartilage to smooth muscle decreases. In the bronchioles, the cartilage is gone, replaced by smooth muscle and elastic fibers.

Bronchi can become infected, inflamed, or irritated. When this happens, you can develop a number of conditions or disorders. These include:

  • Aspiration. The bronchi work hard to keep foreign particles out of the lungs, but sometimes objects like food can make their way in. These inhaled substances can cause infections that lead to pneumonia or other issues.
  • Asthma. This chronic inflammation of the bronchi causes narrowing of the airways. Asthma makes breathing more difficult. It can be mild or severe, and there are many different types.
  • Bronchiectasis. This condition occurs when your bronchi become wider, damaged, and scarred. This makes it difficult to clear the mucus that naturally builds up in the airways.
  • Bronchiolitis. This is a viral lung infection that causes the smallest airways, called bronchioles, to become inflamed. It’s most common in infants.
  • Bronchitis. Irritation or infection in the bronchi can lead to bronchitis. People with bronchitis often have a buildup of phlegm in the lungs. Bronchitis can be short term (acute) or long term (chronic).
  • Bronchopulmonary dysplasia. This condition occurs if an infant’s lungs do not develop properly.
  • Chronic obstructive pulmonary disease (COPD). This is a group of chronic inflammatory lung diseases that cause obstructions in the airways. Chronic bronchitis and emphysema are two of these diseases.
  • Cystic fibrosis. This genetic condition causes the body to produce thick, sticky mucus within the lungs that cannot be cleared out by cilia in the bronchi. It’s a serious condition that makes it harder to breathe. It can cause permanent lung damage.
  • Exercise-induced bronchoconstriction. When people experience symptoms of asthma during exercise, it’s called exercise-induced bronchoconstriction.
  • Lung cancer. Cancer in the bronchi can obstruct the airways and make breathing more difficult.