1. What is the principle function of the proximal convoluted tubule (PCT)?

This structure is the kidney's major site for reabsorption of solutes – in fact, 70% of filtered solutes are reabsorbed at the PCT.

2. What kinds of solute?

The most important are sodium, chloride and potassium ions. In addition, nearly all of the glucose and amino acids filtered by the glomerulus are reabsorbed here.

The first half of the PCT also absorbs phosphate and lactate.

3. Which membrane pump system is key to the PCT reabsorptive abilities?

The Na+-K+ ATPase pump.

4. What are the basic functions of the loop of Henle?

• Solute reabsorption: about 20% of filtered sodium, chloride and potassium ions are absorbed in the thick ascending limb of Henle

• Water reabsorption: about 20% of filtered water is absorbed at the thin descending limb of Henle

• Formation of the counter current multiplication system: this is an efficient way of concentrating the urine over a relatively short distance along the nephron with minimal energy expenditure

5. Why there is no water reabsorption at the ascending limb of Henle?

This portion of the loop of Henle is impermeable to water.

6. What is the basic function of the DCT and collecting duct?

• Reabsorption of solute: about 12% of filtered sodium and potassium are absorbed here

• Secretion: variable amounts of potassium and protons are secreted here

• Reabsorption of water: this occurs only at the most distal portions of the DCT and collecting duct, since the more proximal areas are impermeable to water

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