Learning Russian like any other language does not end with grammar. Russian is all the more very lively language, rich in words and expressions which can diverse speech, make it more vivid and picturesque, help to convey thoughts and emotions truly, express a wide range of feelings.
There is a special part of speech in Russian which helps to express feelings and motives - this is interjection. It should be noted that interjection itself does not describe the feeling of a person. It does not contain information about motive. You might as well say interjection is a verbal expression of emotion.
We do not decline interjections and refer them to any part of a sentence.
Interjections can be compound. These are the words which are not derived from other parts of speech but are initially belonged to pronouns category. Here are the examples of such words (as a rule, they are very short):
А (ah), э (yo), у (huh), ах (ah), эх (heh), ну (er), увы (alas) and some other.
There are also compound interjections, derived from a content word: