KEY POINTS

1. The renal tubule reabsorbs filtered substances.

2. Renal tubule function may be assessed by determining fractional excretion and fractional reabsorption rates.

3. The proximal tubule reabsorbs the bulk of filtered solutes.

4. The proximal tubule secretes organic ions.

5. The distal tubule segments reabsorb salts and dilute the tubule fluid.

6. The collecting duct reabsorbs sodium chloride and can secrete or reabsorb potassium.

7. The distal tubule and collecting duct respond to systemic signals to alter salt excretion as required.

8. Aldosterone enhances sodium reabsorption and potassium secretion.

9. Other hormones regulate sodium transport, including angiotensin II, antidiuretic hormone, endothelin, and atrial natriuretic peptide.

W. Calcium is reabsorbed in the distal nephron and connecting segment, regulated by parathyroid hormone, vitamin D₃, and calcitonin.