An uncontrolled diabetic patient may occasionally have glucose appear in the urine. Which of the following statements is the best explanation for this phenomenon ?

Options

A. High plasma levels of glucose cause glucose to be secreted by the proximal tubule.
B. The kidney is a significant site for glucose synthesis, which causes glucose to occasionally appear in urine
C. The high concentration of glucose saturates the reabsorption pumps, causing glucose to appear in the urine
D. The vasa recta transports glucose into urine.

Answer

To answer the question about why glucose may appear in the urine of an uncontrolled diabetic patient, we can analyze the provided options step by step.

### Step-by-Step Solution:

1. **Understanding the Condition**: In uncontrolled diabetes, the blood glucose levels are significantly elevated. This condition is known as hyperglycemia.

**Hint**: Remember that diabetes affects how the body processes glucose.

2. **Role of the Kidneys**: The kidneys filter blood and are responsible for reabsorbing glucose back into the bloodstream. Under normal circumstances, the kidneys can reabsorb all the glucose that is filtered.

**Hint**: Consider how the kidneys function in filtering and reabsorbing substances.

3. **Reabsorption Mechanism**: Glucose is reabsorbed in the proximal convoluted tubule of the nephron through specific transport proteins. These proteins have a maximum capacity, known as the transport maximum (Tm).

**Hint**: Think about the limits of how much glucose can be reabsorbed by the kidneys.

4. **Saturation of Reabsorption Pumps**: When blood glucose levels are excessively high, the concentration of glucose in the filtrate (the fluid filtered by the kidneys) also increases. If this concentration exceeds the transport maximum of the reabsorption pumps, the pumps become saturated.

**Hint**: What happens when the transport proteins are overwhelmed by too much glucose?

5. **Glucose in Urine**: Once the reabsorption pumps are saturated, the excess glucose cannot be reabsorbed and is instead excreted in the urine. This is why glucose appears in the urine of uncontrolled diabetic patients.

**Hint**: Consider the outcome when the kidneys cannot keep up with the amount of glucose present.

6. **Evaluating the Options**:
- **Option A**: Incorrect, as glucose is not secreted by the proximal tubule.
- **Option B**: Incorrect, since the kidneys do not primarily synthesize glucose.
- **Option C**: Correct, as it accurately describes the saturation of reabsorption pumps leading to glucose in urine.
- **Option D**: Incorrect, as vasodilators do not transport glucose into urine.

### Final Answer:
The best explanation for glucose appearing in the urine of an uncontrolled diabetic patient is **Option C**: "The high concentration of glucose saturates the reabsorption pumps causing glucose to appear in the urine."

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