air sacs expand 气囊扩张
The lungs consist of millions of tiny air sacs.
肺包含数百万个小肺泡。
Anatomically precise support for the heel and ankle, air sacs for extra spring and comfort each year bring apparent new refinements.
在结构上来说，对脚跟和脚踝的恰好支撑，还有气囊带来的额外弹性和舒适度，每年都会有明显的改进。
The air sacs are surrounded by a dense network of minute blood vessels, or capillaries, which connect to the heart.
这些气囊被连接着心脏的浓密的毛细血管网包围着。
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