Preposition question

[TutorT]

Hi All, I'm a little confused.... In the following sentences - I am up against the odds. AND - I am up against the wall, etc, is the word "up" part of a prepositional phrase - up against? Or is "against" the only preposition in the sentence?
thanks heaps

[Syl]

up against : close to or in contact with: crowds pressed up against the police barricades.

(informal) confronted with: I began to think of what teachers are up against today.

up against are both prepositions:)