Anatomy & Organs

Bronchiolus – structure, function & diseases


bronchiole is a small branch of the bronchi . It belongs to the lower respiratory tract . A solitary inflammation of the bronchioli is called bronchiolitis .

What is a bronchiole?

The bronchioles are part of the lung tissue. The lung tissue is the tissue that makes up the lungs . It is formed on the one hand from the bronchi and on the other hand from the alveoli . The alveoli are the structural elements of the lungs. This is where the gas exchange between the blood and the inhaled air takes place.

The bronchi are also part of the airways. The tubular structures lead from the trachea to the lungs and transport the breathing air to the alveoli. The bronchioles are the smallest sections of the bronchi. The trachea initially divides into two main trunks at the so-called bifurcation. Out of these bronchi principalis dexter et sinister toward smaller branches. The bronchi lobaris superior, medius and inferior form the so-called bronchial tree. They ensure ventilation of the right or left lung.

The lobar bronchi are divided into ten segmental bronchi on the right and nine on the left. These are also called bronchi segmentales. The segmental bronchi give rise to the lobular bronchi (bronchi lobulares) and finally the bronchioli.

Anatomy & Structure

The bronchioli can be divided into bronchioli, terminal bronchioli and respiratory bronchioli. In contrast to the bronchial branches, the small branches of the bronchi have no cartilage and no seromucous glands.Seromucous glands produce liquid mucus. The diameter of the bronchioles is less than one millimeter. They are lined with a single layer of ciliated epithelium. In contrast to the rest of the respiratory tract, the cells here are cubic and not cylindrical. Between the epithelial cells are mucus-producing goblet cells, neuroendocrine cells, and scavenger cells. The scavenger cells of the bronchioli are called Clara cells. Clara cells are specialized cells of the respiratory epithelium. Underneath the respiratory epithelium lies a muscular layer. The muscles are smooth and therefore cannot be controlled voluntarily.

The bronchioles branch into four to five terminal bronchioles. These terminal bronchioles are the last segment of the air-carrying airways. They in turn branch into the respiratory bronchioles (Bronchioli respiratorii). The respiratory bronchioles are among the gas-exchanging parts of the airways. There are isolated air sacs (alveoli) in their wall. The respiratory bronchioles end in the alveolar sacs (saccus alveolaris) directly above the ducts of the alveoli (ductus alveolares).

Function & Tasks

The bronchioles are primarily used for air transport. During inhalation, the air enters the trachea via the mouth or nose and from there into the two main trunks. Via the branched bronchial tree, the air is conducted further to the bronchioli, which bring the air to the alveoli. The bronchioles, like the bronchi, also have defense functions. They are lined with ciliated epithelium.

The ciliated epithelium consists of small hairs that can move independently. They beat towards the oral cavity in a common rhythm . Foreign bodies, dust particles and pathogens get caught on the cilia and in the mucus that is produced in the goblet cells of the bronchioli epithelium. With the movement of the ciliated epithelium, they are transported towards the oral cavity. There the pathogens or particles are swallowed and rendered harmless in the stomach by the gastric acid . The Clara cells of the bronchioli epithelium also have an immune function. They secrete various proteins that serve the immune system. This includes the Clara cell secretory protein.

Surfactant factor components are also secreted by the Clara cells. The surfactant proteins SP-A and SP-D have an antimicrobial effect. They also act as opsonins . Opsonins are proteins that play a role in mediating phagocytosis . They are therefore an important part of the immune system. The opsonins of the Clara cells facilitate the scavenger cells of the alveoli , the so-called alveolar macrophages, the phagocytosis of pathogens, allergens and dust particles. Apparently, the Clara cells also assume a reserve function for cell replacement in the airways.


Inflammation of the bronchioli is also known as bronchiolitis. The small bronchioli become inflamed most commonly in young children and infants because their airways are more vulnerable than adult airways.The peak of bronchiolitis is between the ages of three and six months. The disease usually occurs only in the first two years of life. It is striking that children who are not breastfed fall ill more often than children who are breastfed. Children from smoking families also have a higher risk of developing the disease. The main triggers of bronchiolitis are respiratory syncytial viruses ( RS viruses ). The disease usually begins in spring or winter. Influenza viruses or adenoviruses can also cause bronchiolitis. The pathogens are usually transmitted via droplet infection .

The pathogens enter the body through the mucous membrane of the nose or through the conjunctiva. Adenoviruses in particular can also be transmitted via contaminated objects such as toys. The incubation period is between two and eight days, depending on the pathogen. After the entry of the pathogen, there is a rapid multiplication on the mucous membrane of the bronchi. Depending on the course, a distinction can be made between acute and persistent bronchiolitis. However, persistent bronchiolitis is much less common. It is observed almost exclusively in infections with adenoviruses.

The bronchioles have a very small diameter, so that the inflammation-related swelling of the bronchial mucosa leads to a significant restriction in breathing. Accordingly, typical symptoms are coughing , rapid and shallow breathing, the flaring of the nostrils when inhaling and exhaling and the drawing in of the chest. The respiratory symptoms are accompanied by fever and fatigue . In most cases, bronchiolitis heals on its own after a week.

Typical & common bronchial diseases

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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.