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After the lung buds have formed, they begin to grow and branch forming a primitive version of the bronchial tree, determining how the lobes of the lung will be arranged in the mature organ. [2] The first stage of alveolar development, spanning between the fifth and the 16th week of development, is called the pseudoglandular stage . [ 5 ]
A bronchus (/ ˈ b r ɒ ŋ k ə s / BRONG-kəs; pl.: bronchi, / ˈ b r ɒ ŋ k aɪ / BRONG-ky) is a passage or airway in the lower respiratory tract that conducts air into the lungs.The first or primary bronchi to branch from the trachea at the carina are the right main bronchus and the left main bronchus.
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.
At the end of the fourth week, the lung bud divides into two, the right and left primary bronchial buds on each side of the trachea. [56] [57] During the fifth week, the right bud branches into three secondary bronchial buds and the left branches into two secondary bronchial buds. These give rise to the lobes of the lungs, three on the right ...
The afferents of the tracheobronchial glands drain the lungs and bronchi, the thoracic part of the trachea and the heart; some of the efferents of the posterior mediastinal glands also end in this group.
It is defined as ratio between the thickness of the submucosal mucus secreting glands and the thickness between the epithelium and cartilage that covers the bronchi. The Reid index is not of diagnostic use in vivo since it requires a dissection of the airway tube, but it has value in post mortem evaluations and for research.
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The submucosal glands are a companion to goblet cells which also produce mucus, and are found lining the same tubes. [2] In the upper respiratory system of mammals there are submucosal glands in the airways, notably in the sinuses, the trachea and the bronchial tubes. [1] In the visual systems of mammals. In the auditory systems of mammals.