A membranous structure in a hollow organ or passage, as in an artery or a vein, that folds or closes to prevent the return flow of the body fluid passing through it.

• 瓣，瓣膜在中空器官或管道，例如静脉或动脉血管中的膜状结构，能够收紧或关闭以防止通过其的体液倒流