How are the kidneys involved in controlling blood volume? How is the volume of blood in the body related to arterial pressure?

Explanation

The activation of Rennin - Angiotensin - Aldosterone (RAA) system causes increased sodium retention by the kidneys, which leads to reduced water loss into the urine, and therefore it results in blood volume expansion. When formation of angiotensin II, is blocked due to drugs, it enhances sodium and water loss there by reducing the blood volume. Hence any mechanism or drug that alters the activity of the RAA system will affect blood volume. Changes in the blood volume affects atrial pressure by changing cardiac output. Increase in the blood volume increases the atrial pressure.