Which of the following statement(s) is/are true concern renal tubular acidosis?

a. Renal tubular acidosis is primarily caused by reduction in ammonia excretion

b. The renal tubular defect in renal tubular acidosis can either be at the distal or proximal renal tubule

The impaired ability of the kidney to excrete acid and hence generate bicarbonate may be secondary to a decrease in the number of functioning nephrons and is termed uremic acidosis or renal tubular acidosis. Renal tubular acidosis, which can occur both in acute and chronic renal failure, is primarily caused by reduction in ammonia excretion secondary to a reduction in the number of functioning proximal tubular cells. In addition, decreased proximal tubular bicarbonate reabsorption contributes to the development of acidosis. Although the onset of uremic acidosis is related to declining renal function, its appearance may be influenced by diet-dependent protein and organic anion ingestion. Renal tubular acidosis may be classified as distal or proximal, depending on the primary site of the renal tubular defect leading to acidosis. In renal tubular acidosis with hyperkalemia, the mechanism is decreased luminal negativity secondary to impaired sodium reabsorption. In distal renal tubular acidosis with hypokalemia, mechanisms including increased tubular permeability with backleak of secreted H+ into the tubular cell and reduced H+ pump activity are proposed mechanisms.