AP BIOLOGY

Detailed explanation-1: -The proximal convoluted tubule avidly reabsorbs filtered glucose into the peritubular capillaries so that it is all reabsorbed by the end of the proximal tubule. The mechanism for glucose reabsorption was described in Chapter 7.4. The proximal tubule is the only site for glucose reabsorption.

Detailed explanation-2: -Under normal circumstances, up to 180 g/day of glucose is filtered by the renal glomerulus and virtually all of it is subsequently reabsorbed in the proximal convoluted tubule.

Detailed explanation-3: -The proximal tubules reabsorb about 65% of water, sodium, potassium and chloride, 100% of glucose, 100% amino acids, and 85-90% of bicarbonate.

Detailed explanation-4: -Firstly, the glucose in the proximal tubule is co-transported with sodium ions into the proximal convoluted tubule walls via the SGLT2 cotransporter.

Detailed explanation-5: -Most of the glucose entering the tubular system is reabsorbed along the nephron segments, primarily in the proximal tubule, such that urine is almost free of glucose. This is different in diabetes, where the filtered glucose exceeds the transport capacity of the tubular system for glucose and glucosuria occurs.