Why are the kidneys essential to regulate drastic changes in blood pressure?

Answer 1

All of your blood flows through the kidneys. Everything is filtered there. They help control sodium levels in the blood - which in essence controls fluid balance. Heck, the more urine your kidney's put out, the lower the blood pressure.

Then again, is the key word to your question "drastic" changes? I'll have to mull on that one for a bit.

Here, we'll cheat a bit, here's the Wiki answer, "Aldosterone stimulates an increase in the reabsorption of sodium ions from the kidney tubules which causes an increase in the volume of water that is reabsorbed from the tubule. This increase in water reabsorption increases the volume of blood which ultimately raises the blood pressure."

Again, it's from the Renin-Angiotensin System article.

Answer 2

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