Aldosterone - Blood volume and blood pressure

Question

I was doing this problem that asks:

What would happen to blood volume and blood pressure if aldosterone deficiency (failure to reabsorb Na ) were to occur in the kidney?

The answer is: decreased blood volume and decreased pressure

Can someone tell me why this happens?

Answer 1

Failure to reabsorb Na means that there will be a high concentration of Na in the precursor to urine. As the precursor goes through the kidneys water will move down the osmotic gradient into the urine precursor. This will reduce the water content of the blood, and thus its volume and pressure.

Answer 2

Within the nephron,  aldosterone is used to increase blood volume, which causes to increase blood pressure.  Now the mechanism is via Na+

reabsorption. With each Na+ taken in from the collecting duct,  water is also reabsorbed with it.   Now,  if it fails to take Na in, the water can't be reabsorbed and will be secreted as urine., which will lead to lowered blood volume and BP.  

Addison's disease is a condition with low alsdosterone.