Monday 15 October 2012
Definition: A bronchus (plural bronchi, adjective bronchial) is a passage of airway in the respiratory tract that conducts air into the lungs. The bronchus branches into smaller tubes, which in turn become bronchioles. No gas exchange takes place in this part of the lungs.
Main bronchi or pulmonar bronchi
The human trachea (windpipe) divides into two main bronchi (also mainstem bronchi), the left and the right, at the level of the sternal angle and of the fifth thoracic vertebra or up to two vertebrae higher or lower, depending on breathing, at the anatomical point known as the carina. The right main bronchus is wider, shorter, and more vertical than the left main bronchus.
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 pneumonia may result. If the endotracheal tube used for intubation is inserted too far, it usually lodges in the right mainstem bronchus. This allows ventilation of the right lung, but leaves the left lung useless.
The right main bronchus subdivides into three lobar bronchi, while the left main bronchus divides into two.
The lobar bronchi divide into tertiary bronchi, also known as segmental bronchi, each of which supplies a bronchopulmonary segment. A bronchopulmonary segment is a division of a lung 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.
superior segmental bronchus of right lower lobe (Nelson bronchus)
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 two to 11 alveolar ducts. There are five or six alveolar sacs associated with each alveolar duct. The alveolus is the basic anatomical unit of gas exchange in the lung.
Bronchitis is 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 bronchitis is a form of COPD, usually associated with smoking or long-term exposure to irritants.
Asthma is hyperreactivity of the bronchi with an inflammatory component, often in response to allergens.