Function of "up" in verb phrases functioning as a noun?

What part of speech is the word "up" playing in these verb phrases that function as nouns?

Mix-up

Smash up

Meet up

Pop up

Pin up

Hold up

Stick up

These never seem to be used as nouns.

Show up

Beat up

Take up

Give up

Ante up

Put up

These are used as nouns and verbs.

Beat down

Take down

Thanks for you response, John. This is an interesting form of speech. In doing some research on this topic, I found an interesting paper titled, "VERB-PARTICLE NOMINALS IN ENGLISH," accessed at: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.453.8819&rep=rep1&type=pdf

The author of this paper says:

"Particles in English can appear to the right or left of a stem—verb, noun, or adjective—to produce a verbal, nominal, or adjectival construction. All of these patterns are productive in English (albeit with diachronic variableness), but none occur without directional constraint in certain cases. For example, there is income (n.), come in (phrasal verb), but no to income (v.) or a come in (nominal).

"Since early Modern English one of the most productive patterns in English has been the verb-particle construction. The verb-particle verbal combination (e.g., run down, bring about, cast off, play on, bowl over, blend in, come by, bounce back, dish up, etc.), commonly called phrasal verbs, is extremely productive with thousands of examples catalogued in stand-alone dictionaries, receiving extensive scrutiny in the literature, seeking the explanation for their combinatorial constraints. The verb-particle nominal construction, on the other hand, although less common than the verbal counterpart, is still a fixture in both spoken and written English today.

"Only in Late Middle English to Early Modern English did the verb-particle nominal form become evident (gravup 1324, runabout 1377, lean-to 1453, sit-up 1483, startup 1517, passover 1530, runaway 1547, put by 1549, put off 1549, pass-by 1550, wind-up 1573, start-away 1578, hang-by 1579, pull-down 1588, stand-up 1590, hop-about 1593, Walkup 1595, sneakup 1596)."