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The bronchioles (/ ˈ b r ɑː ŋ k i oʊ l s / BRONG-kee-ohls) are the smaller branches of the bronchial airways in the lower respiratory tract. They include the terminal bronchioles, and finally the respiratory bronchioles that mark the start of the respiratory zone delivering air to the gas exchanging units of the alveoli .
A bronchopulmonary segment is a portion of lung supplied by a specific segmental bronchus and its vessels. [1] [2] These arteries branch from the pulmonary and bronchial arteries, and run together through the center of the segment. Veins and lymphatic vessels drain along the edges of the segment.
Bronchial atresia is a rare congenital disorder that can have a varied appearance. A bronchial atresia is a defect in the development of the bronchi, affecting one or more bronchi – usually segmental bronchi and sometimes lobar. The defect takes the form of a blind-ended bronchus.
Further divisions of the segmental bronchi (1 to 6 mm in diameter) [7] are known as 4th order, 5th order, and 6th order segmental bronchi, or grouped together as subsegmental bronchi. [8] [9] Compared to the 23 number (on average) of branchings of the respiratory tree in the adult human, the mouse has only about 13 such branchings.
The lobar bronchi branch into tertiary bronchi also known as segmental bronchi and these supply air to the further divisions of the lobes known as bronchopulmonary segments. Each bronchopulmonary segment has its own (segmental) bronchus and arterial supply. [8] Segments for the left and right lung are shown in the table. [5]
It branches off into two bronchial tubes, a left and a right main bronchus. The bronchi branch off into smaller sections inside the lungs, called bronchioles. These bronchioles give rise to the air sacs in the lungs called the alveoli. [10] The lungs are the largest organs in the lower respiratory tract.
Bronchial buds continue to branch as development progresses until all of the segmental bronchi have been formed. Beginning around week 13, the lumens of the bronchi begin to expand in diameter. By week 16, respiratory bronchioles form. The fetus now has all major lung structures involved in the airway.
The nodules may also have a segmental or lobar distribution. Air alveolograms and air bronchograms can also be seen which indicate fluid in the alveoli with air in the terminal bronchioles indicating disease is alveolar. [1] These findings appear soon after the onset of symptoms and change rapidly thereafter.