**Question:** The glucose transporter which is stimulated by insulin is located in:

A. Insulin-sensitive tissues
B. Liver cells
C. Muscle cells
D. Fat cells

**Core Concept:** Insulin is a hormone produced by the pancreas that plays a crucial role in regulating blood glucose levels. One of its actions is to facilitate glucose uptake into cells, particularly in insulin-sensitive tissues like liver, muscle, and adipose tissue.

**Why the Correct Answer is Right:** The correct answer is D: Fat cells (adipocytes). Insulin stimulates glucose uptake in adipocytes by increasing the expression and activity of glucose transporter type 4 (GLUT4), a specific glucose transporter. GLUT4 is responsible for facilitating glucose transport across the cell membrane and plays a critical role in glucose homeostasis.

**Why Each Wrong Option is Incorrect:**

A. Insulin-sensitive tissues (including liver, muscle, and adipose tissue) all have glucose transporters that are stimulated by insulin, but adipocytes are specifically mentioned because they are the correct answer.

B. Liver cells (hepatocytes) contain glucose transporters, but the correct answer is adipocytes, as insulin stimulates glucose uptake in adipocytes and not liver cells.

C. Muscle cells (myocytes) have glucose transporters that are stimulated by insulin, but adipocytes are specifically mentioned because they are the correct answer.

**Clinical Pearl:** Insulin-stimulated glucose uptake in adipocytes plays a vital role in maintaining glucose homeostasis, preventing hyperglycemia and reducing the risk of type 2 diabetes mellitus. A better understanding of this process aids in appreciating the importance of insulin action on glucose transport in different cell types.