A bronchiolus is a small branch of the bronchi. It belongs to the lower respiratory tract. Solitary inflammation of the bronchioli is called bronchiolitis.
What is a bronchiolus?
The bronchioli are part of the lung tissue. Lung tissue is the tissue that makes up the lungs. It is formed partly by the bronchi and partly by the alveoli. The alveoli are the structural elements of the lungs. This is where the exchange of gases between the blood and the inhaled air takes place. The bronchi are also part of the respiratory tract. These tubular structures lead from the trachea to the lungs and transport the air breathed to the alveoli. The bronchioles are the smallest sections of the bronchi. The trachea first divides into the two main trunks at the so-called bifurcation. From these bronchi principalis dexter et sinister against smaller branches arise. The bronchi lobaris superior, medius and inferior form the so-called bronchial tree. They provide ventilation to the right or left lung. The lobar bronchi in turn divide 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 to the bronchioli.
Anatomy and structure
The bronchioli can be divided into bronchioli, bronchioli terminales, and bronchioli respiratorii. The small branches of the bronchi, unlike the bronchial branches, no longer have cartilage or seromucous glands. Seromucous glands produce liquid mucus. The diameter of bronchioles is less than one millimeter. They are lined with a single-layered ciliated epithelium. Unlike the rest of the respiratory tract, the cells here are cubic rather than cylindrical. Between the epithelial cells are mucus-producing goblet cells, neuroendocrine cells, and phagocytes. The phagocytes of the bronchioli are called Clara cells. Clara cells are specialized cells of the respiratory epithelium. Beneath the respiratory epithelium is a layer of musculature. The musculature is smooth and thus cannot be controlled at will. The bronchioles each branch into four to five bronchioli terminales. These terminal bronchioles are the last segment of the air-transporting airways. They in turn branch into the respiratory bronchioles (bronchioli respiratorii). The respiratory bronchioles belong to the gas-exchanging parts of the respiratory tract. In their wall there are isolated pulmonary alveoli (alveoli). The bronchioli respiratorii terminate in the alveolar sacs (saccus alveolaris) directly above the ducts of the alveoli (ductus alveolares).
Function and Tasks
The bronchioles serve primarily to transport air. During inhalation, air enters the trachea via the mouth or nose and from there into the two main trunks. Through the branched bronchial tree, the air is further conveyed to the bronchioli, which bring the air to the alveoli. However, similar to the bronchi, the bronchioli also perform defensive functions. They are lined with ciliated epithelium. The ciliated epithelium consists of small hairs that can move independently. They beat in a common rhythm in the direction of the oral cavity. Foreign bodies, dust particles and pathogens get stuck on the cilia and in the mucus produced in the goblet cells of the bronchiolar epithelium. With the movement of the ciliated epithelium, they are transported toward the oral cavity. There, the pathogens or particles are swallowed and rendered harmless in the stomach by gastric acid. The Clara cells of the bronchiolar epithelium also have an immune function. They secrete various proteins that serve the immune defense. These include the Clara cell secretory protein. Components of surfactant factor are also secreted by Clara cells. The surfactant proteins SP-A and SP-D have antimicrobial activity. They also function as opsonins. Opsonins are proteins that play a role in mediating phagocytosis. Thus, they are an important part of the immune defense system. Clara cell opsonins facilitate the phagocytosis of pathogens, allergens, and dust particles by the phagocytic cells of the alveoli, called alveolar macrophages. Apparently, Clara cells also perform a reserve function for cell replacement in the airways.
Diseases
Inflammation of the bronchioli is also known as bronchiolitis.Small bronchiolitis is most common in infants and young children because their airways are more susceptible than adult airways. The peak of the disease of bronchiolitis is between three and six months of age. Normally, the disease occurs only in the first two years of life. It is striking that children who are not breastfed get sick more often than breastfed children. Children from smoking families also have a higher risk of contracting the disease. The main triggers of bronchiolitis are respiratory syncytial viruses (RS viruses). The disease usually begins in the 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 entry of the pathogens, rapid multiplication occurs on the mucous membrane of the bronchial tubes. Depending on the course, a distinction can be made between acute and persistent bronchiolitis. Persistent bronchiolitis, however, is much rarer. It is observed almost exclusively in infections with adenoviruses. The bronchioles have only a very small diameter, so that the swelling of the bronchial mucosa due to inflammation leads to a significant restriction in breathing. Typical symptoms include coughing, rapid and shallow breathing, flaring of the nostrils during inhalation and exhalation, and chest constriction. Respiratory symptoms are accompanied by fever and fatigue. In most cases, bronchiolitis heals on its own after one week.
Typical and common bronchiolitis
- Bronchitis
- Irritative cough
- Chronic bronchitis
- Asthma
