Which statement best describes proximal tubule reabsorption?

Which statement best describes proximal tubule reabsorption?

• A. The proximal tubule reabsorbs a wide range of substances including water, Na+, glucose, amino acids, and bicarbonate
• B. The proximal tubule reabsorbs only water
• C. The proximal tubule reabsorbs none of the filtered solutes
• D. The proximal tubule reabsorbs all electrolytes except bicarbonate

Answer: (D)

The proximal tubule reclaims a broad array of the filtered load, making it the major site for reabsorption of both water and many solutes. It uses sodium-linked transport mechanisms to bring in glucose and amino acids, and it also reabsorbs bicarbonate through a carbonic anhydrase–driven process that couples with Na+ reabsorption. In fact, most of the filtered bicarbonate is reabsorbed in this segment. Because of this extensive reabsorption of multiple solutes, the description that fits best is that the proximal tubule reabsorbs a wide range of substances including water, Na+, glucose, amino acids, and bicarbonate. The claim that it reabsorbs all electrolytes except bicarbonate isn’t correct, since bicarbonate is reabsorbed here as well, along with other electrolytes.

The proximal tubule reclaims a broad array of the filtered load, making it the major site for reabsorption of both water and many solutes. It uses sodium-linked transport mechanisms to bring in glucose and amino acids, and it also reabsorbs bicarbonate through a carbonic anhydrase–driven process that couples with Na+ reabsorption. In fact, most of the filtered bicarbonate is reabsorbed in this segment. Because of this extensive reabsorption of multiple solutes, the description that fits best is that the proximal tubule reabsorbs a wide range of substances including water, Na+, glucose, amino acids, and bicarbonate. The claim that it reabsorbs all electrolytes except bicarbonate isn’t correct, since bicarbonate is reabsorbed here as well, along with other electrolytes.