Bronchi: Anatomy, Function, and 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. Pvc Shrink Films

Bronchi: Anatomy, Function, and Treatment

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 include bronchitis, 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.

The bronchi begin at the base of the trachea at the level of the fifth thoracic vertebra near 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.

The bronchi begin at the bottom of the trachea at a ridge of cartilage called the carina. The carina divides into two branches: the right bronchus and the left bronchus.

The right bronchus delivers 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.

The left bronchus delivers 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 10 bronchopulmonary segments in the right bronchi and eight to 10 in the left.

The bronchopulmonary segments subdivide into progressively smaller passageways known as bronchioles. These further divide into progressively smaller and narrower bronchioles that have different functions.

Air first enters the conducting bronchioles, then moves to the terminal bronchioles before entering the respiratory 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.

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.

The bronchi are made of a combination of tissue, including a few types of cartilage, smooth muscle, and mucous membranes.

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 cartilage provides 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 cartilage in 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.

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.

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 as ciliated 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 as simple cuboidal epithelium.

The mucous membranes of the bronchioles and alveoli take on a flatter shape and are known as simple squamous epithelium.

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.

The cilia in the upper part of the airway traps viruses and bacteria in mucus and helps move them away from the lungs. This can be done by coughing to expel phlegm or swallowing, which forces them into the digestive tract, where the body can dispose of them.

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.

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 requires general 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.

In acute 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 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.

Most cases of chronic bronchitis in the United States are caused by long-term cigarette smoking. Long-term exposure to secondhand smoke, air pollution, and chemical fumes can also play a role.

Chronic bronchitis is one manifestation of chronic 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.

Asthma is an illness characterized by constriction of the bronchi (bronchospasm), which in turn interferes with the passage of air from the environment to the alveoli of the lungs.

Allergies, exercise, or irritants can trigger asthma attacks in people with asthma.

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.

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 is caused by a viral infection, most commonly respiratory 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.

A rare and severe type of bronchiolitis, called bronchiolitis obliterans (also known as "popcorn lung"), is a chronic illness mainly affecting adults.

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 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 cancer is 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 cancer is responsible for around 15% of lung cancers. These aggressive lung cancers may not be found until they have metastasized (spread to other body parts).

A bronchopleural fistula is an abnormal passageway (a sinus tract) that develops between the bronchi and the space between the membranes that line the lungs (the pleural cavity).

It is a serious complication often caused by lung cancer surgery but may also develop after chemotherapy, radiation, or an infection. Bronchopleural fistula is a rare but dangerous condition that is fatal in 25% to 71% of cases.

The following common imaging tests are used to diagnose problems that involve the bronchi.

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. A computed tomography (CT) scan is needed. This imaging uses multiple X-rays to create a 3-D image.

During a bronchoscopy, 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.

An endobronchial ultrasound can 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.

Because many different conditions and diseases can affect the bronchi, treatments vary widely, ranging from medications and rehabilitation to surgery.

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.

These medications help relax the muscles around the air passages, which makes breathing easier by widening the airway openings. They are a mainstay of asthma treatment and are usually administered via a nebulizer or an inhaler with a spacer.

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 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.

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.

Hand-held devices, including Oscillating Positive Expiratory Pressure (PEP) and Intrapulmonary Percussive Ventilation (IPV) devices, can help break up mucus.

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.

People with lung cancer may receive radiation, chemotherapy, surgery, and immunotherapy medications, depending on the stage and extent of their cancer.

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.

Pulmonary rehabilitation is performed by a respiratory therapist who monitors your condition and works with you to strengthen your airways and improve oxygen intake.

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. 

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By Lynne Eldridge, MD  Lynne Eldrige, MD, is a lung cancer physician, patient advocate, and award-winning author of "Avoiding Cancer One Day at a Time."

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Bronchi: Anatomy, Function, and Treatment

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