Nephrology gives me a cold sweat

Just began studying the kidney, hint, the study of it may never end.  My initial thoughts are that it exists to filter waste from the blood which is a nice service to the function of the body, but more critical is its role in maintenance of blood pressure.  BP too high?  Excrete water.  BP too low?  Retain sodium.  According to Dr. Najeeb each kidney actually has over one million blood pressure and sodium sensors.  Now is this the reason for those sudden urges to pee 35 miles before the next rest stop?  An amazing system, that I probably abuse daily out of ignorance.  It tirelessly maintains my body in homeostasis despite repeated stresses, the coffee, the protein, oh my.