Name = Bronchus
GraySubject = 237
GrayPage = 1084
Caption = Conducting passages.
Caption2 = Front view of cartilages of larynx, trachea, and bronchi.
System = respiratory
pulmonary branches of vagus nerve
MeshName = Bronchi
MeshNumber = A04.411.125
DorlandsPre = b_23
DorlandsSuf = 12198294
A bronchus (plural bronchi, adjective bronchial) is a caliber of airway in the
respiratory tractthat conducts air into the lungs. [cite book
last = Maton
first = Anthea
coauthors = Jean Hopkins, Charles William McLaughlin, Susan Johnson, Maryanna Quon Warner, David LaHart, Jill D. Wright
title = Human Biology and Health
publisher = Prentice Hall
date = 1993
location = Englewood Cliffs, New Jersey, USA
isbn = 0-13-981176-1] No
gas exchangetakes place in this part of the lungs.
The trachea (windpipe) divides into two main bronchi (also mainstem bronchi), the left and the right, at the level of the
sternal angle. The right main bronchusis wider, shorter, and more vertical than the left main bronchus. The right main bronchus subdivides into three segmental bronchi while the left main bronchus divides into two. The lobar bronchi divide into tertiary bronchi. Each of the segmental bronchi supplies a bronchopulmonary segment. A bronchopulmonary segment is a division of a lung that is separated from the rest of the lung by a connective tissue septum.. This property allows a bronchopulmonary segment to be surgically removed without affecting other segments. There are ten segments per lung, but due to anatomic development, several segmental bronchi in the left lung fuse, giving rise to eight. The segmental bronchi divide into many primary bronchioles which divide into terminal bronchioles, each of which then gives rise to several respiratory bronchioles, which go on to divide into 2 to 11 alveolar ducts. There are 5 or 6 alveolar sacs associated with each alveolar duct. The alveolus is the basic anatomical unit of gas exchange in the lung.
hyaline cartilagepresent 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 muscleis present continuously around the bronchi.
mediastinum, at the level of the fifth thoracic vertebra, the trachea divides into the right and left primary bronchi. The bronchi branch into smaller and smaller passageways until they terminate in tiny air sacs called alveoli.
cartilageand mucous membraneof the primary bronchi are similar to that in the trachea. As the branching continues through the bronchial tree, the amount of hyaline cartilagein the walls decreases until it is absent in the smallest bronchioles. As the cartilage decreases, the amount of smooth muscle increases. The mucous membrane also undergoes a transition from ciliated pseudostratified columnar epithelium to simple cuboidal epitheliumto simple squamous epithelium.
alveolar ductsand alveoliconsist primarily of simple squamous epithelium, which permits rapid diffusion of oxygenand carbon dioxide. Exchange of gases between the air in the lungs and the blood in the capillariesoccurs across the walls of the alveolar ducts and alveoli.
Role in disease
Bronchitisis defined as inflammation of the bronchi. There are two main types: acute and chronic. Acute bronchitis is usually caused by viral or bacterial infections. Chronic bronchitisis a form of COPD, usually associated with smoking or long-term exposure to irritants. Asthmais hyperreactivity of the bronchi with an inflammatory component, often in response to allergens.
While the left mainstem bronchus departs from the trachea at an angle, the right mainstem bronchus is almost a vertical continuation of the trachea. This anatomy predisposes the right lung to several problems:
*If food, liquids, or foreign bodies are aspirated, they often will lodge in the right mainstem bronchus.
Aspiration pneumoniamay result.
endotracheal tubeused for intubationis inserted too far, it usually lodges in the right mainstem bronchus. This allows ventilation of the right lung, but leaves the left lung useless.
*Patients with inadequate
coughreflexes may develop chronic right middle lobe lung infections such as the Lady Windermere Syndrome.
* Moore, Keith L. and Arthur F. Dalley. "Clinically Oriented Anatomy, 4th ed." (1999). ISBN 0-7817-5936-6
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