Human urine is usually acidic because
- potassium and sodium exchange generates acidity
- hydrogen ions are actively secreted into the filtrate
- the sodium transporter exchanges one hydrogen ion for each sodium ion, in peritubular capillaries.
- excreted plasma proteins are acidic
Answer
(2) hydrogen ions are actively secreted into the filtrate
Solution
As per NCERT, the proximal convoluted tubule (PCT) and distal convoluted tubule (DCT) help to maintain the pH and ionic balance of the body fluids by selective secretion of hydrogen ions, ammonia and potassium ions into the filtrate.
∵ H+ ions are actively secreted into the filtrate (and HCO3- is reabsorbed), the urine becomes acidic (average pH ≈ 6).
∵ Plasma proteins are not filtered or excreted normally.
∴ Human urine is usually acidic because hydrogen ions are actively secreted into the filtrate.
Answer: (2)