Sentence:  The natural anatomical and physiological defensive features of the upper respiratory tract , such as the turbinates of the nose and the cilia of the trachea and larger bronchi , are capable of impinging out the larger <WSD>particles</WSD> to which we are ordinarily exposed in our daily existence . 
Meaning of the word marked with <WSD> tags:  (nontechnical usage) a tiny piece of anything