Na is transported across the peritubular membrane by Na,K-ATPase. This segment also is water impermeable. Na is passively reabsorbed down its electrochemical gradient through Na channels. Peritubular Na transport is by the activity of Na,K-ATPase. Regulation of Na reabsorption occurs in these segments.
Aldosterone is a steroid hormone that is produced and secreted by the adrenal glands.
The adrenal glands are located adjacent to the anterior pole of the kidney. Angiotensin II, formed through the renin-angiotensin system, stimulates the release of aldosterone. I circulating in the blood to angiotensin II which circulates to the adrenal glands and stimulates aldosterone secretion. Aldosterone increase ATP production by the mitochondria to provide more energy for Na,K-ATPase. Thus, without compensation, a decrease in GFR would produce Na excess and increased GFR would produce a Na deficit.