Which of the following is reabsorbed along with sodium in early poion of proximal tubules?
**Core Concept**
Reabsorption of ions and water in the proximal tubules is a critical process for maintaining electrolyte balance and fluid homeostasis in the body. This process is primarily driven by the reabsorption of sodium ions, which creates an osmotic gradient that facilitates the reabsorption of other solutes and water.
**Why the Correct Answer is Right**
Glucose is reabsorbed along with sodium in the early portion of the proximal tubules through a sodium-glucose cotransporter (SGLT2). This cotransporter is a membrane-bound protein that uses the energy from the electrochemical gradient of sodium ions to transport glucose molecules from the lumen into the renal epithelial cells. This process is essential for maintaining normal blood glucose levels and preventing excessive glucose loss in the urine.
**Why Each Wrong Option is Incorrect**
* **Option A:** Glutamine is reabsorbed in the proximal tubules, but it is not reabsorbed along with sodium in the same manner as glucose.
* **Option B:** Amino acids are reabsorbed in the proximal tubules, but the primary mechanism of reabsorption is through a sodium-amino acid cotransporter, which is different from the sodium-glucose cotransporter.
* **Option D:** Bicarbonate ions are reabsorbed in the proximal tubules, but the primary mechanism of reabsorption is through the sodium-bicarbonate cotransporter, which is also different from the sodium-glucose cotransporter.
**Clinical Pearl / High-Yield Fact**
The sodium-glucose cotransporter (SGLT2) is a key target for the treatment of diabetes mellitus, and inhibitors of this enzyme have been developed as a novel class of antidiabetic medications.
**Correct Answer:** C. Glucose.