Glucose is absorbed

Options

A. Passively by DCT
B. Actively by DCT
C. Actively by PCT
D. Passively by PCT

Answer

### Step-by-Step Solution:

1. **Understanding Glucose Absorption**: Glucose is a vital nutrient for the body, primarily absorbed in the kidneys.

2. **Renal Threshold**: The renal threshold is the maximum concentration of a substance in the blood that can be reabsorbed by the kidneys before it starts appearing in urine. For glucose, this threshold is approximately 180 mg/dL.

3. **Glycosuria**: When blood glucose levels exceed the renal threshold (180 mg/dL), glucose will start to appear in the urine, a condition known as glycosuria. This is not normal and typically indicates a pathological condition, such as diabetes mellitus.

4. **Active Transport in Proximal Convoluted Tubule (PCT)**: Glucose is actively reabsorbed in the proximal convoluted tubule (PCT) of the nephron. This means that glucose is transported against its concentration gradient, which requires energy.

5. **Conclusion**: Under normal physiological conditions, glucose is not found in urine because it is completely reabsorbed by the kidneys until the renal threshold is exceeded. Therefore, the correct answer to the question of glucose absorption is that it is actively absorbed by the PCT.

### Answer:
Glucose is actively absorbed by the proximal convoluted tubule (PCT) of the nephron in the kidneys, and it does not appear in urine until blood glucose levels exceed the renal threshold of 180 mg/dL, leading to a condition known as glycosuria.

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