Bronchioles: anatomy, function and treatment

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Bronchioles are the airways within the lungs that extend from the bronchi like the branches of a tree, the two main airways that carry air out of the windpipe (windpipe) after inhalation through the nose or mouth.

The bronchioles carry air into small sacs called alveoli , where oxygen and carbon dioxide are exchanged. They are vulnerable to conditions such as asthma, bronchiolitis , cystic fibrosis , and emphysema , which can cause narrowing and / or obstruction of the airways.

Anatomy

The bronchioles are part of the lower respiratory tract. As they branch out from the bronchi, they become smaller and smaller, crossing the inside of each lung before ending in groups of alveoli. There are three types, divided by size :

  • Lobular bronchioles (larger passages that enter the lobes of the lungs first)
  • Respiratory bronchioles (two or more branches of each terminal bronchiole, which in turn lead to two to 10 alveolar ducts)
  • Terminal bronchioles (50 to 80 smaller passages in each lung)

Lobular and terminal bronchioles are sometimes called "dead space" because there is no air exchange in these tubes.

The bronchioles themselves are tiny, 0.3 to 1 mm in diameter .

Composition

Bronchioles rely on bundles of protein fibers called elastin to maintain their shape by anchoring themselves in lung tissue .

The lining of the bronchioles, called the lamina propria, is thin and surrounded by a layer of smooth muscle that contracts when blood flow decreases and expands when blood flow increases.

The walls of the bronchioles are also lined with tiny finger-like projections called cilia, whose job is to remove debris and germs from the airways. The density of the cilia decreases as the bronchioles branch and become smaller and smaller.

The bronchioles are lined with club cells that secrete surfactants, compounds that reduce surface tension in the airways, allowing them to expand during inhalation and prevent them from collapsing during exhalation .

Club cells also secrete enzymes that break down waste and irritants so they can be easily removed from the lungs.

Function

The function of the bronchioles is to carry air into a diffuse network of about 300 million alveoli in the lungs. When you inhale, oxygenated air enters the bronchioles. The carbon dioxide collected by the alveoli is then expelled from the lungs when you exhale.

The bronchioles are not inert. The smooth muscles that surround the airways automatically contract (close) and expand (open) to control the flow of air in and out of the lungs.

Related conditions

Dilation of the airways (bronchodilation) occurs when the lungs require more oxygen, such as during exercise or at high altitudes.

On the contrary, the narrowing of the airways, the narrowing of the bronchi can occur when irritants or allergens are inhaled. While this is intended to prevent foreign matter from entering the lungs, it can restrict breathing, sometimes severely. Certain medications, inflammations, and diseases can do the same .

Symptoms of bronchospasm include:

  • Difficulty breathing and shortness of breath.
  • Chest tightness
  • Cough
  • Cyanosis (blue skin due to lack of oxygen)
  • Severe stress fatigue
  • Wheezing

Bronchospasm can be accompanied by a bronchiolar obstruction caused by a blockage in the airways, such as excessive mucus production. Symptoms of bronchiolar obstruction can overlap with symptoms of bronchospasm and include:

  • Chronic productive cough
  • Chest tightness
  • Cyanosis
  • Recurrent respiratory infections
  • Wheezing

The following conditions are associated with bronchioles:

Asthma

Asthma is an allergic condition caused by mainly due to allergens or irritants in the air, and in children, respiratory infections. When allergens enter the bronchioles, an immune cell called mast cells releases a substance called histamine that causes the smooth muscles in the bronchioles to contract.

Bronchiolitis

Bronchiolitis is an inflammation of the bronchioles. It is most common in babies between 3 and 6 months of age who contract a virus such as respiratory syncytial virus (RSV) or influenza .

Obliteration of bronchiolitis

Obliterative bronchiolitis is a rare inflammatory disorder that causes scarring (fibrosis) of the bronchioles to the point of blocking the airways.

Obliterative bronchiolitis, called popcorn lung, mainly affects adults and can be caused by :

  • Excessive or prolonged exposure to toxins such as ammonia, chlorine, formaldehyde, sulfur dioxide, nicotine, diacetyl (used to flavor oils), and acetaldehyde (found in e-cigarettes)
  • Organ transplant
  • Prolonged inhalation of fiberglass particles or coal fly ash;
  • Rheumatoid arthritis and other autoimmune diseases.
  • Viral infections of the lungs, including coronavirus (COVID-19)

Elimination of bronchiolitis is irreversible: in severe cases, a lung transplant may be necessary.

Cystic fibrosis

Cystic fibrosis is a life-threatening inherited disease that affects the lungs and digestive system.

Cystic fibrosis causes goblet cells to produce excessive amounts of mucus, which clogs the tubes, ducts, and ducts of the respiratory and gastrointestinal tracts. As the disease progresses, this can cause scarring of the bronchioles and collapse of the lung (atelectasis) .

There is no cure for cystic fibrosis, but it can be slowed down with medications, antibiotics, physical therapy, and vaccines.

Emphysema

Emphysema is one of the manifestations of congestive obstructive pulmonary disease (COPD), a group of lung diseases that block air flow and make breathing difficult. In emphysema, damage to the alveoli and lung tissue causes the bronchioles to collapse .

The main cause of emphysema is smoking. Others include air pollution, secondhand smoke, chronic respiratory infections, and exposure to dust and chemicals in the workplace.

Emphysema cannot be reversed, but it can be treated with bronchodilators, anti-inflammatory drugs, supplemental oxygen, and surgery to remove damaged tissue.

Treatment and rehabilitation

The course and duration of bronchiolar rehabilitation can vary depending on whether the condition is restrictive and / or obstructive. Some treatments are designed to relieve acute episodic symptoms (called flare-ups), while others prevent symptoms from getting worse or coming back.

Restrictive disorders

Rehabilitation and treatment options for bronchospasm include :

  • Avoid triggers such as allergens or environmental pollutants. This is a key aspect of asthma treatment .
  • Biologics , such as Xolair (omalizumab), that block the release of histamine in people for whom antihistamines don't work.
  • Oral or inhaled bronchodilators, including beta-adrenergic agonists like albuterol , anticholinergics like Spiriva (tiotropium), and methylxanthines like aminophylline
  • Inhaled corticosteroids , such as Flovent HFA (fluticasone) or QVAR RediHaler (beclomethasone), to reduce the frequency and severity of exacerbations.
  • Oral corticosteroids , such as prednisone , to treat exacerbations.
  • Oral leukotriene modifiers such as Singulair (montelukast) and Zyflo (zileuton), which help control airway inflammation.

Obstructive disorders

Acute conditions like bronchiolitis may require only short-term treatment to cure the underlying infection.

Chronic bronchiolar obstruction, as in COPD and cystic fibrosis, generally requires medication, physical therapy, and supportive care to slow the progression of the disease. Sometimes surgery is required.

Rehabilitation and treatment options for bronchiolar obstruction include :

  • Airway cleaning devices , including high intensity oscillators or positive expiratory pressure (PEP), to help clear mucus.
  • Bronchodilators to open airways blocked by mucus buildup.
  • Diaphragmatic breathing : inhale and exhale through the abdomen, not through the chest, to increase lung capacity.
  • Inhaled corticosteroids to reduce inflammation caused by the blockage.
  • Mucolytics that thin mucus, making coughing easier.
  • Nasal suction to remove excess mucus from the nasal passages and upper respiratory tract.
  • Oxygen therapy to provide supplemental oxygen to people with chronic breathing difficulties, either continuously or as needed.
  • Pulmonary rehabilitation , which includes techniques such as postural drainage and percussion , for regular mucus clearance in people with chronic bronchiolar obstruction.

Additionally, many people with chronic obstructive disorders like COPD and cystic fibrosis may find 20 to 30 minutes of exercise, five days a week, a beneficial part of treatment .

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