Well, an interjection is a part of speech, so they're words of often indiscernable meaning.

I like the observation about the topography above. However, I must say that one of the brightest, most creative women I know uses uhs regularly in speech--and her topography is rich and broad. I like her by far too much to suggest that she drain those swamps. It's worth wading through them to get over to the mountains to which she ascends. Ah [that's an interjection, too], what vistas she provides!