Each of these sections has a main function in adjusting the amount and kind of solutes in the urine. Different drugs and diuretics work at distinct areas, some diuretics are potassium sparing while others (like Lasix/furosemide) are potassium wasting.
Check out this Cartoon on how your thyroid works. Thyroid issues can get complicated, so this might help explain a little bit better what dotors do not explain to their patients. Check out that T-shirt here: