Table of ContentsView AllTable of ContentsAnatomyTissueFunctionAssociated ConditionsDiagnosisTreatment
Table of ContentsView All
View All
Table of Contents
Anatomy
Tissue
Function
Associated Conditions
Diagnosis
Treatment
The bronchi are the two large tubes that carry air from the windpipe (trachea) into the lungs and back out again. A crucial part of the respiratory system, the bronchi function primarily as passageways for air, bringing oxygen into the lungs and expelling carbon dioxide.
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.
The bronchi also play an essential role in immune function. They trap and remove viruses, bacteria, and other pathogens that can make you sick. Medical conditions that affect the bronchi includebronchitis, asthma, chronic obstructive pulmonary disease (COPD), and lung cancer.
This article explains the bronchi anatomy and function. It also describes different conditions that affect the bronchi and how they are treated.
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Anatomy of the Bronchial Tree
The bronchi begin at the base of the trachea at the level of the fifththoracic vertebranear the sternum.
The trachea, bronchi, and bronchioles are known as the bronchial tree because it looks like an upside-down tree. The trachea is the trunk, the bronchi are the limbs, the bronchioles are the branches, and the alveoli are the leaves.
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.
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.
What Are Alveoli?
Bronchial Tissue
The bronchi are made of a combination of tissue, including a few types of cartilage, smooth muscle, and mucous membranes.
Cartilage
Cartilage is a strong but flexible soft tissue made of collagen and elastin fibers and proteoglycan, a filler material. 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 type 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 network 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.
Mucosal Tissue
The inside of the bronchial tree is covered with a moist lining known as mucous membranes. Glands in the mucous membrane make a thick, slippery fluid known as mucus or phlegm.
Mucosal tissue in the bronchi contains:
The type of mucosal tissue in the bronchi changes as it divides into smaller segments.
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.
Anatomy of the Trachea
Bronchi Function
The bronchi function primarily as a passageway for air as it travels from the mouth and trachea down to the alveoli and back out of the body.
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. Some of these involve other regions of the lungs, and others are restricted to the main bronchus and small bronchi.
Aspiration of Foreign Objects
If a foreign object is accidentally inhaled, it often becomes lodged in one of the bronchi. People who have trouble eating and swallowing—after a stroke, for example—are prone to aspirating food.
In people who are unconscious, such as during surgery that requiresgeneral anesthesia, there is a risk the person could vomit and aspirate some of it. (This is why people are told to fast before surgery.) Inhaled substances can then attract bacteria, leading to aspiration pneumonia.
Acute Bronchitis
Inacute bronchitis, a viral infection usually starts in the nose or throat and then affects the cells of the bronchi, causing them to swell. Common symptoms of bronchitis include a cough that often involves coughing up phlegm and wheezing.
Chronic Bronchitis
Chronic bronchitis causes inflammation in the bronchioles, causing a heavy mucus buildup in the lungs that is ongoing (versus acute, which is short-term). Symptoms include a chronic cough and a susceptibility to bacterial infections; eventually, breathing becomes increasingly difficult.
COPD
Chronic bronchitis is one manifestation ofchronic obstructive pulmonary disease.Emphysema, which involves damage to the alveoli, often accompanies bronchitis. COPD is a serious disease that can lead to low oxygen levels, respiratory failure, and lung cancer, and is often fatal.
Differences Between Chronic Bronchitis and Emphysema
Asthma
Allergies, exercise, or irritants can trigger asthma attacks in people with asthma.
What Is a Bronchospasm?A bronchospasm occurs when your airways constrict (narrow), causing wheezing and difficulty breathing. Bronchospasms are a symptom of many conditions that affect the airways, including asthma, seasonal allergies, and COPD.
What Is a Bronchospasm?
A bronchospasm occurs when your airways constrict (narrow), causing wheezing and difficulty breathing. Bronchospasms are a symptom of many conditions that affect the airways, including asthma, seasonal allergies, and COPD.
Bronchiectasis
When the walls of the bronchi become irreversibly scarred, they can thicken, causing mucus to build up and become a breeding ground for bacteria. Over time, there is a decrease in lung function.
Bronchiectasis is usually associated with other illnesses, such as COPD, cystic fibrosis, and recurrent cases of pneumonia.
Bronchiolitis
A rare and severe type of bronchiolitis, calledbronchiolitis obliterans(also known as “popcorn lung”), is a chronic illness mainly affecting adults.
Bronchopulmonary Dysplasia
Bronchopulmonary dysplasia (BPD) can occur in newborns (usually those who are premature) who are being treated with oxygen or are on a ventilator for another breathing problem.
The high amounts of oxygen and pressure used in these therapies can overstretch the alveoli, inflaming and damaging the inside lining of the airways.In some cases, BPD can have lifelong effects.
Bronchogenic Carcinoma
Bronchogenic carcinoma is an older term for cancers in the bronchi and bronchioles. Now this term is used interchangeably with lung cancer of all types.Non-small cell lung canceris the most common, responsible for 80% to 85% of cancers.
This type of lung cancer is more commonly found in non-smokers, women, and young adults.Small cell lung canceris responsible for around 15% of lung cancers. These aggressive lung cancers may not be found until they have metastasized (spread to other body parts).
Bronchopleural Fistula
Abronchopleural fistulais an abnormal passageway (a sinus tract) that develops between the bronchi and the space between the membranes that line the lungs (thepleural cavity).
How Bronchial Conditions Are Diagnosed
The following common imaging tests are used to diagnose problems that involve the bronchi.
Computed Tomography (CT)
A chest X-ray is often the first procedure used to visualize the lungs. 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.
Bronchoscopy
During abronchoscopy, a tube called a bronchoscope is inserted through the mouth and into the bronchi.
A bronchoscopy may evaluate symptoms such as a persistent cough or coughing blood. Still, it can also treat some conditions, such as bleeding in the airways or removing a foreign body.
Endobronchial Ultrasound
Anendobronchial ultrasoundcan look at tissues deeper in the lungs past the bronchial walls.
When a tumor is located, a needle biopsy may be performed under the guidance of the endobronchial ultrasound, making it possible to obtain tissue from a tumor without needing an open lung biopsy.
Treating Bronchial Issues
Because many different conditions and diseases can affect the bronchi, treatments vary widely, ranging from medications and rehabilitation to surgery.
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.
Bronchodilators
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
When a bronchial condition leads to low oxygen levels in the blood, supplemental oxygen is often necessary, either temporarily for an acute illness or permanently, as with a chronic disease such as COPD.
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.
Airway Clearance Devices
Hand-held devices, including Oscillating Positive Expiratory Pressure (PEP) and Intrapulmonary Percussive Ventilation (IPV) devices, can help break up mucus.
Chest Physical Therapy (CPT)
CPT is a technique for loosening mucus that involves clapping on the chest in a certain way. Electronic chest clappers and vests are now available to help perform this technique.
Cancer Treatments
People with lung cancer may receive radiation, chemotherapy, surgery, and immunotherapy medications, depending on the stage and extent of their cancer.
Pulmonary Rehabilitation
Pulmonary rehabilitation is a type 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.
It consists of two large airway tubes that start at the bottom of the trachea and split into progressively smaller structures on the right and left sides of the lungs. The smallest part of the bronchi is the bronchioles, which end at the alveoli, where oxygen is exchanged for carbon dioxide that travels back through the bronchi as we exhale.
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.
12 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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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.
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