## Core Concept
The transport maximum (Tm) of glucose in renal tubules refers to the maximum rate at which glucose can be reabsorbed by the renal tubules. This concept is crucial in understanding renal physiology and glucose handling by the kidneys. The reabsorption of glucose in the renal tubules is primarily facilitated by **sodium-glucose cotransporters** (SGLTs) in the proximal convoluted tubule.

## Why the Correct Answer is Right
The correct answer, . The proximal convoluted tubule has a high capacity for glucose reabsorption, which is nearly complete under normal conditions. This reabsorption is facilitated by **sodium-glucose cotransporter 2 (SGLT2)**, which has a high transport capacity. The Tm for glucose is approximately 325 mg/min in a normal adult. When the plasma glucose concentration exceeds the threshold for glucose reabsorption (about 180 mg/dL), the transport maximum is exceeded, and glucose appears in the urine.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because it does not accurately represent the transport maximum of glucose in renal tubules. Without a specific value, it's hard to directly refute, but typically, Tm values are given in specific units like mg/min.
- **Option B:** This option is incorrect for similar reasons as option A; it lacks specificity and does not align with known physiological values for glucose transport maximum.
- **Option D:** This option is incorrect as it suggests a much lower transport maximum than what is physiologically known.

## Clinical Pearl / High-Yield Fact
A key clinical pearl is that the **threshold for glucose appearance in urine** is around 180 mg/dL. This threshold is slightly below the transport maximum because it represents the plasma concentration at which glucose starts to appear in the urine due to the saturation of reabsorption mechanisms. Remembering that the Tm for glucose is about **325 mg/min** can help in understanding how the kidneys handle glucose under different conditions.

**Correct Answer: .**