An aneurysm is an outpouching of a vessel, which weakens its wall even further.

动脉瘤是指血管的突出，进一步增加了管壁的脆弱性。

These outpouchings are called alveoli, and there are about 500 million of them within the lungs.

这些突起称为肺泡，在肺部大约有5亿个肺泡。