The bronchi branch off into progressively smaller structures that make up the bronchial tree.
It divides to the right and left, then subdivides further into bronchioles.
It ends at the alveoli, tiny sacs in the lungs that exchange oxygen for carbon dioxide.
magicmine / Getty Images
The bronchi also play an essential role in immune function.
They trap and remove viruses, bacteria, and other pathogens that can make you sick.
This article explains the bronchi anatomy and function.
It also describes different conditions that affect the bronchi and how they are treated.
Carina
The bronchi begin at the bottom of the trachea at a ridge of cartilage calledthe carina.
The carina divides into two branches: the right bronchus and the left bronchus.
Right and Left Bronchi
Theright bronchusdelivers air to the right lung.
It is shorter and more vertical than the left, approximately 1 inch (2.5 cm) long.
It divides into three smaller bronchi, which enter the three lobes of the right lung.
Theleft bronchusdelivers air to the left lung.
This tube is narrower but longer than the right bronchus, approximately 1.5 inches (5 cm) long.
It divides into two secondary lobar bronchi, which enter the two lobes of the left lung.
The bronchi divide further into 10bronchopulmonary segmentsin the right bronchi and eight to 10 in the left.
Bronchioles
The bronchopulmonary segmentssubdivide into progressively smaller passageways known asbronchioles.
These further divide into progressively smaller and narrower bronchioles that have different functions.
Air first enters theconducting bronchioles, then moves to theterminal bronchiolesbefore entering therespiratory bronchioles.
What Is the Difference Between Bronchi and Bronchioles?
As the bronchi divide and become smaller, they become narrower airways known as bronchioles.
The bronchioles are made of different tissue than the bronchi and play a different role in respiration.
Alveoli
The bronchial tree ends at the alveoli.
Air moves from the respiratory bronchioles to the alveolar ducts and into the alveolar sacs.
These tiny air sacs contain capillaries that exchange oxygen for carbon dioxide, a waste product of metabolism.
The lungs expel carbon dioxide when we exhale.
Cartilage connects muscles, bones, and organs and takes different forms depending on its function.
Hyaline cartilageprovides the structure that keeps the bronchi from collapsing during inhalation and exhalation.
This firm, C-shaped bang out of cartilage makes up the trachea, carina, and upper bronchi.
Elastic cartilagein the smaller bronchi provides flexibility that allows the lungs to expand and contract.
It is made of a threadlike web connection of elastic fibers that are flat like plates.
As the bronchi subdivide into smaller bronchi, they contain progressively less cartilage.
Smooth Muscle
As the amount of cartilage decreases, the smaller bronchi contain more smooth muscle tissue.
Once the smaller bronchi divide into bronchioles, they are primarily smooth muscle and no longer contain cartilage.
Glands in the mucous membrane make a thick, slippery fluid known as mucus or phlegm.
The mucous membrane at the top of the bronchi is known asciliated pseudostratified columnar epithelium.
This tissue contains more cilia to filter pathogens and dust out of incoming air.
As the bronchi divide into smaller segments, the mucosal tissue becomes cube-shaped cells known assimple cuboidal epithelium.
The mucous membranes of the bronchioles and alveoli take on a flatter shape and are known assimple squamous epithelium.
The bronchi are critical in respiration, allowing the body’s tissues to receive oxygen.
They also transport carbon dioxide to exit the body.
The mucus membrane lining the bronchi moisturizes the air as it enters the lungs and protects against infectious agents.
It provides a meaningful “barrier” to inhaled pathogens that can help prevent infections from taking hold.
What Conditions Affect the Bronchi?
Several medical conditions can affect the bronchi.
People who have trouble eating and swallowingafter a stroke, for exampleare prone to aspirating food.
(This is why people are told to fast before surgery.)
Inhaled substances can then attract bacteria, leading to aspiration pneumonia.
Common symptoms of bronchitis include a cough that often involves coughing up phlegm and wheezing.
Symptoms include a chronic cough and a susceptibility to bacterial infections; eventually, breathing becomes increasingly difficult.
Most cases of chronic bronchitis in the United States are sparked by long-term cigarette smoking.
Long-term exposure to secondhand smoke, air pollution, and chemical fumes can also play a role.
Allergies, exercise, or irritants can trigger asthma attacks in people with asthma.
What Is a Bronchospasm?
A bronchospasm shows up when your airways constrict (narrow), causing wheezing and difficulty breathing.
Over time, there is a decrease in lung function.
Bronchiolitis
Bronchiolitis is due to a viral infection, most commonlyrespiratory syncytial virus(RSV).
The bronchioles swell and fill with mucus, making breathing difficult.
Infants under three months old are the most likely to be affected by this disease.
Bronchogenic Carcinoma
Bronchogenic carcinoma is an older term for cancers in the bronchi and bronchioles.
These aggressive lung cancers may not be found until they have metastasized (spread to other body parts).
Bronchopleural fistula is a rare but dangerous condition that is fatal in 25% to 71% of cases.
However, it lacks the sensitivity or resolution required to diagnose bronchial conditions.
Acomputed tomography (CT) scanis needed.
This imaging uses multiple X-rays to create a 3-D image.
A bronchoscopy may evaluate symptoms such as a persistent cough or coughing blood.
Endobronchial Ultrasound
Anendobronchial ultrasoundcan look at tissues deeper in the lungs past the bronchial walls.
Antibiotics
Antibiotics are usually prescribed when a bacterial infection affects the bronchial passages, such as bronchitis.
They are not used to treat viral infections, which often clear on their own.
They are a mainstay of asthma treatment and are usually administered via anebulizeror an inhaler with a spacer.
Corticosteroids
These drugs reduce and prevent inflammation within the lungs.
They help reduce swelling in the airways and decrease the amount of mucus produced.
Like bronchodilators, they can be given via a nebulizer or an inhaler with a spacer.
Expectorants
Expectorants are a medication that thins mucus and makes it easier to expel.
The expectorant guaifenesin is found in many over-the-counter cold and cough remedies.
Oxygen therapy is provided in hospitals but can also be used with home-based equipment.
Oxygen is usually delivered through an oxygen cannula (nasal prongs) or a face mask.
Electronic chest clappers and vests are now available to help perform this technique.
Pulmonary Rehabilitation
Pulmonary rehabilitation is a throw in of respiratory therapy used to treat bronchial conditions.
It can involve breathing exercises that are done at home, specialized equipment, and oxygen.
Summary
The bronchi serve an essential role in respiration.
They bring oxygen-rich air deep into the lungs and expel carbon dioxide from the body.
The bronchi comprise different types of cartilage, smooth muscle, and mucosal tissue.
It acts as a protective layer to trap and remove airborne pathogens and prevent infections.
Medical conditions affecting the bronchi include bronchitis, asthma, COPD, and cancer.
These are often diagnosed using imaging tests like X-ray, ultrasound, and bronchoscopy.
Treatments include different medications, respiratory therapy, and sometimes surgery.
National Cancer Institute.Bronchi, bronchial tree, & lungs.
Saladin KS.Anatomy & Physiology: The Unity of Form and Function.
McGraw Hill LLC; 2024.
2016;19(2):159-168. doi:10.1016/j.chom.2016.01.001
American Lung Association.Chronic bronchitis.
University of Iowa Stead Family Children’s Hospital.Overview of asthma.
American Lung Association.Learn about bronchiectasis.
American Lung Association.Learn about bronchiolitis.
American Lung Association.Learn about bronchopulmonary dysplasia.
Salik I, Vashisht R, Sharma S, Abramowicz AE.Bronchopleural fistula.
StatPearls Publishing; 2024.
UC San Diego Health.Endobronchial ultrasound (EBUS).
American Lung Association.Treating and managing bronchiectasis.
