Renin and Aldosterone

[reising1]

It seems that the kidney secretes renin when blood volume is low, and renin cleaves angiotensin into angiotensin I, which is converted to angiotensin II. Angiotensin stimulates release of aldosterone from the adrenal cortex. (as per Examkrackers).

But here's where I get confused: doesn't aldosterone decrease blood volume?

So why would renin be secreted when blood volume is low if it only further decreases blood volume?

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[ashtray81]

Aldosterone INCREASES blood volume by increasing sodium reabsorption in the tubules. Water, in turn, always follows sodium, so an increase in Na+ will cause water to be reabsorbed as well back into the capilliaries.