Question

Human urine is usually acidic because:

• A. Hydrogen ions are actively secreted into the filtrate
• B. The sodium transporter exchanges one hydrogen ion for each sodium ion, in peritubular capillaries
• C. Excreted plasma proteins are acidic
• D. Potassium and sodium exchange generates acidity

Answer 1

The correct option is A Hydrogen ions are actively secreted into the filtrate

In the DCT, hydrogen ions are actively secreted into the tubular filtrate, so as to maintain the acid balance of the blood. This increases the acidity of urine.
Plasma proteins do not get excreted out in urine. And potassium-sodium exchange cannot generate acidity because one cation is being exchanged for another.
The sodium transporter however, that exchanges sodium for a hydrogen ion does play a crucial role in increasing acidity of urine, but unlike what the statement says it functions in the PCT and in the intercalary cells of the DCT and not in the peritubular capillaries. Peritubular capillaries are involved in the uptake of reabsorbed substances from the renal medulla back into blood.