Question

how do kidneys help maintain pH? What is the countercurrent multiplier mechanism?

Answer 1

either through secreting H+ or bicarbanoate, by intercalated called types a and b respectively in the distant collecting ducts

Answer 2

and through the secretion of buffers, especially ammonia

Answer 3

Thanks, complete awesomeness!! =3

Answer 4

You will find a very clear animation on counter current multiplication here:
http://www.colorado.edu/intphys/Class/IPHY3430-200/countercurrent_ct.html

Hope this helps