Question: How DO the kidneys control blood pressure?

Keith Siew answered on 28 Jun 2013:

The kidneys can control the amount of salt in our bodies… if you excrete salt you will lose water in your urine… so the kidneys can control the amount of water in our bodies too… this will alter the volume of blood in our cardiovascular system and can either increase or decrease the blood pressure.

The kidneys can also instruct the bone marrow with a hormone called EPO to make more red blood cells and increase the thickness of the blood which can effect blood pressure.

Finally the kidneys can release hormones like Renin that is part of a system called the RAAS (Renin-Aldosterone-Angtiotensin-System) which can effect how much the blood vessels contract… so this is yet another point that the kidneys can control blood pressure