breathing system

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During breathing in: (1) Air enters the breathing system through the nose (or the mouth) (2) Air travels along the [blank_start]trachea[blank_end] and then the two [blank_start]bronchi[blank_end]. (3) Air travels along smaller and smaller tubes. (4) Air reaches the [blank_start]air[blank_end] [blank_start]sacs[blank_end] at the end of the smallest tubes.

Gaseous exchange inside the lungs  The trachea branched to two [blank_start]bronchi[blank_end] (singular: bronchus).  Each bronchus divides into smaller and smaller tubes, ending in a large number of [blank_start]air[blank_end] [blank_start]sacs[blank_end].  The air sacs are surrounded by tiny blood vessels ([blank_start]blood[blank_end] [blank_start]capillaries[blank_end]).  The blood in the blood vessel flowing from other parts of the body carries higher [blank_start]carbondioxide[blank_end] content and lower [blank_start]oxygen[blank_end] content.  Gaseous exchange occurs between through the thin wall of the air sac and blood vessels.  Carbon dioxide leaves the [blank_start]blood[blank_end] to the [blank_start]air[blank_end] and oxygen enters the blood from the air.

compare with inhaled air, exhaled air contains [blank_start]less[blank_end] oxygen, [blank_start]more[blank_end] carbon dioxide, [blank_start]more[blank_end] water vapour, has a [blank_start]higher[blank_end] temperature