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What happens to water and glucose in the proximal convoluted tubule?
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renal system
Diagram showing the location of the kidneys in the abdominal cavity and their attachment to major arteries and veins.
In the proximal convoluted tubule, both water and glucose are reabsorbed from the glomerular filtrate back into the blood capillaries surrounding the tubule.123
- Glucose: Under normal physiological conditions, all glucose present in the filtrate is completely reabsorbed in the proximal tubule. However, this process has a maximum reabsorptive capacity; if plasma glucose levels become excessively high—such as in cases of diabetes—the glucose arrives at the tubule cells faster than it can be processed, resulting in the excretion of the surplus in the urine.12
- Water: Approximately 70 to 80 percent of the water in the filtrate is reabsorbed in this section. This process occurs passively in response to the active reabsorption of sodium ions. Because the tubule is highly permeable to water, it moves to follow the sodium, which helps maintain the fluid within the tubular lumen at a concentration roughly isosmotic with the original glomerular filtrate.13