I don't think there is any one resource that magically lets you understand and answer them. The "arrow questions" are really just a way of asking you four or five things all in one question.
My advice for how to approach them... read the question, and figure out one of the variables that you know you understand. So if they say that renin is high in the stem, and you know that aldosterone is going to go up, then focus on that. Look at all of the choices where aldosterone is not increased and mark them out. Then move to the next variable that you understand, and mark out all remaining options that do not fit what that one variable does. You can usually very quickly get your choices down to two or three (sometimes just one), in those first two "easy" variables.
There's usually a variable or two that is trickier to understand, but it helps if you get rid of the other answer choices first so that you can focus on just that part.
IMO, it's much tougher to try to assemble in your head all of the things that you think are going to happen (this up, that down, this down, that up...) and then look for the corresponding answer choice. Even when you understand it all, it's too easy to make a careless error that way, and if you don't understand it all you feel lost. Be systematic. Rule out what you know you can rule out. Get it down to only the parts of the question/variables you aren't as sure about, and then if you have to take a guess at least your odds are much better.
