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The ducts number between two and eleven from each bronchiole. [10] Each duct opens into five or six alveolar sacs into which clusters of alveoli open. Each terminal respiratory unit is called an acinus and consists of the respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli. New alveoli continue to form until the age of eight years.
alveolar duct. alveolar sac. alveolus; At each division point or generation, one airway branches into two smaller airways. The human respiratory tree may consist on average of 23 generations, while the respiratory tree of the mouse has up to 13 generations. Proximal divisions (those closest to the top of the tree, such as the bronchi) mainly ...
The terminal bronchioles are the most distal segment of the conducting zone. They branch off the lesser bronchioles. Each of the terminal bronchioles divides to form respiratory bronchioles which contain a small number of alveoli. Terminal bronchioles are lined with simple ciliated cuboidal epithelium containing club cells. Club cells are non ...
The respiratory bronchiole gives rise to the alveolar ducts that lead to the alveolar sacs, which contain two or more alveoli. [20] The walls of the alveoli are extremely thin allowing a fast rate of diffusion. The alveoli have interconnecting small air passages in their walls known as the pores of Kohn. [20]
Alveolar glands, also called saccular glands, are glands with a saclike secretory portion, in contrast with tubular glands. They typically have an enlarged lumen (cavity), hence the name: they have a shape similar to alveoli , the very small air sacs in the lungs.
This blood gas barrier is extremely thin (in humans, on average, 2.2 μm thick). It is folded into about 300 million small air sacs called alveoli [23] (each between 75 and 300 μm in diameter) branching off from the respiratory bronchioles in the lungs, thus providing an extremely large surface area (approximately 145 m 2) for gas exchange to ...
Within the lungs, the ventilation process specifically involves organs like respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli. For the perfusion process, the circulatory organs of the cardiovascular system such as the heart, pulmonary arteries, pulmonary veins, and alveolar capillaries are involved.
Collateral ventilation is a back-up system of alveolar ventilation that can bypass the normal route of airflow when airways are restricted or obstructed. The pathways involved include those between adjacent alveoli ( pores of Kohn ), between bronchioles and alveoli (canals of Lambert), and those between bronchioles (channels of Martin).