A bronchus (plural bronchi, adjective bronchial) is a caliber of airways in the the respiratory tract that conducts air into the lungs. No gas exchange takes place in this part of the lungs.
The trachea (windpipe) divides into two main bronchi, the left and the right. These subdivide in two (left lung) or three (right lung) bronchi that each serve one lobe. The bronchi divide several more generations until they become bronchioles. There is a bronchus going to each segment of each lobe of the lung. Bronchi are generally greater than one millimetre in diameter.
There is still cartilage present in the bronchi, present as irregular rings in the larger bronchi (and not as regular as in the trachea), and as small plates and islands in the smaller bronchi. Smooth muscle is present continuously around the bronchi.
Role in disease
Bronchitis is viral or bacterial infection of the bronchi. Asthma is hyperreactivity of the bronchi with an inflammatory component, often in response to allergens. Chronic bronchitis (COPD) is smoking- or coal dust-induced chronic inflammation of the bronchi that leads to obstruction of the airways.
961) is a cartilaginous and membranous tube, extending from the lower part of the larynx, on a level with the sixth cervical vertebra, to the upper border of the fifth thoracic vertebra, where it divides into the two bronchi, one for each lung.
The first cartilage is broader than the rest, and often divided at one end; it is connected by the cricotracheal ligament with the lower border of the cricoid cartilage, with which, or with the succeeding cartilage, it is sometimes blended.
It consists of areolar and lymphoid tissue, and presents a well-marked basement membrane, supporting a stratified epithelium, the surface layer of which is columnar and ciliated, while the deeper layers are composed of oval or rounded cells.
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