**Core Concept**
GLUT3 is a glucose transporter that plays a crucial role in the uptake of glucose in cells, particularly in neurons and red blood cells. It is a member of the facilitative glucose transporter family and is responsible for basal glucose uptake in the brain.

**Why the Correct Answer is Right**
GLUT3 is primarily located in neurons, where it facilitates the uptake of glucose for energy production. This is essential for maintaining proper neuronal function, particularly in the brain. GLUT3 has a high affinity for glucose, allowing it to transport glucose even at low glucose concentrations.

**Why Each Wrong Option is Incorrect**
**Option A:** GLUT3 is not primarily located in the kidney, which is the primary site of glucose reabsorption in the body. While GLUT3 is present in the kidney, it is not its primary location.

**Option B:** GLUT1 is another glucose transporter, but it is not the same as GLUT3. GLUT1 is primarily located in the blood-brain barrier, red blood cells, and the placenta, where it facilitates glucose transport to these tissues.

**Option C:** GLUT2 is a glucose transporter primarily located in the liver, pancreas, and small intestine, where it plays a role in glucose sensing and regulation of glucose metabolism.

**Option D:** GLUT4 is a glucose transporter primarily located in adipose tissue and skeletal muscle, where it is insulin-responsive and plays a key role in glucose uptake in response to insulin.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that GLUT3 has a high affinity for glucose, making it a critical transporter for maintaining proper neuronal function, particularly in the brain.

**Correct Answer:** D. GLUT4 is primarily located in adipose tissue and skeletal muscle.