Bronchial tree


The bronchial tree is aptly named for its resemblance to the branches of a tree, as larger tubes perpetually concede to smaller tube in an intricate framework of branches. Right around the level of the sternal angle, just posterior to the manubrium, the trachea splits off into the right and left primary bronchi. Surrounding the lumen of each extending principle branch, rings of cartilage keep the larger airways open as they branch off into smaller tubes.

The right primary branch lies at a more upright angle, which increases the chances of foreign particles slipping through into the tubular formation. Each principle bronchi is then segregated off once again as it descends into the lungs, forming the lobar and then the segmental bronchi, also known as the secondary and tertiary bronchi, respectively. From there, the network continues to branch off into smaller tubes known as bronchioles.


The bronchioles contain very little cartilage, and are controlled via thicker, smoother muscles. The muscle controls whether or not these smaller airways contract or expand. As it refers to air flow resistance, bronchioles provide the most resistance of the air flow passages, similar to the functions associates with the arterioles in the circulatory system.


Bronchial tree
Image: Bronchial Tree

The inner walls of the bronchi are lined with pseudostratified columnar epithelial cells while the bronchioles are lined with a more simplistic cuboidal epithelium. The network into the air sacs is rather delicate and fine, as numerous terminal bronchioles adjoin with the respiratory bronchioles which then adjoin with the alveolar ducts. The alveolar ducts then lead to the alveolar sacs.


The tubular network inside the lungs is actually divided into two basic sections. The network of air conduction ends at the terminal bronchioles while the respiratory segment starts with the respiratory bronchioles.

The medical condition known as asthma is either the result of an infection or an allergy. An asthma attack means that the smooth muscle in the respiratory bronchioles is going into spasm. The respiratory bronchioles are devoid of cartilage to keep the airway open, and thus the passage of air becomes constricted along with the muscle.
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