Sentence:  The natural anatomical and physiological <WSD>defensive</WSD> 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 particles to which we are ordinarily exposed in our daily existence . 
Meaning of the word marked with <WSD> tags:  intended or appropriate for defending against or deterring aggression or attack