through the proximal tubule into the urine. Nearly all of the water, glucose, potassium, and amino acids are reabsorbed from the renal tubules by passive transfer. Those substances that are ionized remain in the urine and are excreted. The pH of the urine affects reabsorption. In alkaline urine, weak acids are ionized and mostly excreted. In acidic urine, the weak acids are less ionized and will undergo reabsorption. Some drugs and diet influence urinary pH. For example, a high-protein diet results in acidic urine.