Human urine is usually acidic because

Human urine is slightly acidic (pH 6.0) because H⁺ is actively secreted into the filtrate and HCO₃- is reabsorbed. 

(1) Acidity is not related to the exchange of Na⁺ and K⁺.

(3) The Na^+-H⁺ antiporters are found in the epithelial cells of the nephron but not in peritubular capillaries.

(4) Most plasma proteins are slightly acidic but large plasma proteins are neither filtered nor excreted.