BRONCHIOLES: CHARACTERISTICS, FUNCTIONS AND DISEASES - ANATOMY AND PHYSIOLOGY - 2025

The bronchioles are small branches of the bronchi, conductors of the respiratory system, which ensure that the air reaches all parts of the lungs. They are divided into respiratory and terminal bronchioles.

The respiratory system is made up of a pair of lungs and the trachea. When we breathe, we draw air through the mouth or nose, it passes through the pharynx, larynx and trachea, which is the main airway. The trachea is made up of cartilage rings and branches into two bronchi, each corresponding to each lung.

In turn, the bronchi branch several times into even smaller divisions, until these branches are no longer supported by rings of cartilage. These branches are the bronchioles.

These bronchioles, in turn, are subdivided into even smaller terminal bronchioles, still in the conducting zone, which also divide into smaller bronchioles, marking the beginning of the respiratory region.

Characteristics and anatomy of the bronchioles

The bronchial network, like most airways, contains cilia (small cells) on its inner surface to help move air through the entire respiratory system. Starting from the bronchi, the bronchioles branch into terminal bronchioles and respiratory bronchioles.

Bronchioles are approximately 1 mm or less in diameter and their walls consist of ciliated cuboidal epithelium, with a thin inner lining, surrounded by a layer of smooth muscle. The diameter of each type of bronchiole is essential to control air flow, either to increase or decrease it.

Terminal bronchioles

The branching bronchioles divide into terminal bronchioles, even smaller, with a diameter of 0.5 mm or less. These, in turn, branch out and subdivide into smaller bronchioles, the respiratory bronchioles.

Respiratory bronchioles

The terminal bronchioles branch into respiratory bronchioles, these are the narrowest of the airways and are divided into alveolar ducts.

The terminal bronchioles constitute the most distal segment, marking the end of the division conducting airflow in the respiratory system, while the respiratory bronchioles mark the beginning of the respiratory division where gas exchange takes place.

Features

The bronchioles are responsible for conducting air to the alveoli. In addition, they participate in the metabolism of hormones and in the detoxification of toxic substances (xenobiotics).

The primary function of the bronchioles is to ensure that incoming air is supplied to each alveolus. The lungs have millions of alveoli responsible for allowing a high rate of gas exchange with the atmosphere.

To provide air to all the alveoli, the bronchioles successively branch into smaller and smaller bronchioles.

The bronchioles direct and prepare the air before it reaches the alveoli. To do this, they heat the inspired air and moisten it and saturate it with vapor, and subsequently filter it of foreign particles.

The terminal bronchioles also fulfill the important function of decontaminating the inspired air. The airways are lined by a layer of mucus that guarantees humidity and traps the small particles of inspired air, the cilia are in charge of mobilizing it, beating it and directing it towards the larynx.

Bronchioles can also trigger the cough mechanism, due to their sensitivity to corrosive chemical stimuli. In addition to its main function, the pulmonary capillary bed is an important reservoir of blood. It also performs important metabolic actions.

Bronchioles change in diameter to increase or decrease air flow. When there is an increase in diameter, we are faced with bronchodilation, stimulated by adrenaline or the sympathetic nerves to increase air flow.

In its opposite case, when there is a decrease in diameter, it is a bronchoconstriction, stimulated by histamine, parasympathetic nerves, cold air, chemical irritants and other factors to decrease the flow of air.

Related pathologies

Many respiratory diseases can affect the bronchioles. Lacking cartilage to support them, the bronchioles are susceptible to being affected by conditions that cause constriction and / or obstruction of the airways.

When the bronchioles are inflamed or infected, the most common symptoms include:

1. Wheezing
2. Rapid respiratory rate
3. Retraction
4. Nasal flapping (widening of the nostrils)
5. Cyanosis (a bluish tint to the skin due to low oxygen in the blood)

The most common medical conditions that affect the bronchioles include:

Bronchospasm

It occurs when the smooth muscle tissue of the bronchioles contracts, significantly narrowing their diameter and preventing the absorption of oxygen into the blood.

The most common causes are bronchitis, flu, asthma, and respiratory infections. Another cause may be due to anaphylactic shock caused by allergens.

Sometimes bronchospasm occurs due to medications such as beta-blockers and pilocarpine. It is commonly treated with oxygen therapy and bronchodilators.

Bronchiolitis

It is produced by inflammation of the bronchioles. It is a fairly common pathology during the first year of life in children, generally between 3 and 6 months of age.

Its symptoms are pictures of cough, shortness of breath and is usually due to a respiratory syncytial virus. Supportive treatment with oxygen, fluid, and nutrition is usually given through gastric tube or intravenous line.

Obliterative bronchiolitis

It consists of a chronic obstruction of the lower airway, it is a rare and serious disease, with a higher incidence in adults.

It occurs mainly after viral infections. The most common symptoms are non-productive cough (dry cough without mucus) and shortness of breath.

Asthma

It is an inflammatory disease of the airways, which results from a decrease in its diameter (bronchoconstriction). Its symptoms can vary and are recurring.

It usually presents reversible airflow obstruction and bronchospasm. It can also include episodes of wheezing, coughing, shortness of breath, and a feeling of tightness in the chest.

Treatment consists of medications to dilate the airways (bronchodilators), as well as avoid known allergens.

Almost all conditions related to the bronchioles can be treated with oxygen therapy or bronchodilation, or by treating the cause of the disease.

Bronchodilation is accomplished with medication or mechanical manipulation to widen the airways. In severe cases, such as obliterative bronchiolitis, a lung transplant may be necessary.

References

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