Lungs
The lungs have a spongy, elastic structure and are enclosed in the throax. They can be expanded or compressed by the movementof the throax in such a way that the air is repeatedlyy taken in and expelled.
Lung Structure
The trachea divides into two bronchi which enter the lungs and divide into smaller branches. These divide furthur into bronchioles which terminate in a mass of little thin-walled, pouch-like air sacs or aveoli.
Air Passages
Rings of cartilage keep the trachea and bronchi open and prevent their closing up when the pressure inside them falls during inspiration. The lining of the air passaes is covered with numerous cilia. These are minute hairs which constantly flick to and fro. Mucus is secreted by glandular cells, also in the lining. Dust particles, bacteria, etc., which are carried in with the air during inspiration become trapped in the mucus film and,
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