You have to decide if, at the end of the day, you are still happy with your job.
I get very frustrated sometimes b/c I too see things at my job that I know are not right, and need to be changed, but I have no power to do anything about it. But I also have had a pretty honest talk with myself, and I have decided that I like my job anyway and that I dont want to leave right now. So with that decision to stay, I have to be OK with knowing that sometimes I will be frustrated and that I wont always be able to change the things I want to change. So I have to just find ways to deal with my own feelings and move forward anyway. If it ever gets to the point where the frustration is too much and I am not happy anymore, then I will know it is time to move on from my job and find a new one.
When I am "in the moment" and feeling really frustrated (which sometimes makes me react emotionally), I get up and walk away from my desk for 10 minutes. Go outside, get a drink of water, talk to a work friend, or whatever. It gets my mind out of it for a moment, which is normally enough for me to return to business as usual.