**Question:** Which of the following is a correct description of the mechanism of action of insulin in glucose homeostasis?

A. Insulin stimulates gluconeogenesis
B. Insulin inhibits glycolysis
C. Insulin promotes glycogen synthesis
D. Insulin stimulates lipolysis

**Core Concept:** Insulin is a hormone produced by the beta cells of the pancreas, which plays a crucial role in maintaining glucose homeostasis. One of its primary functions is to lower blood glucose levels by facilitating glucose uptake into cells and promoting glucose storage.

**Why the Correct Answer is Right:** Insulin acts on target cells, such as muscle, liver, and adipose tissue, to promote glucose uptake and utilization. Insulin inhibits glycolysis (the initial stage of cellular respiration) and gluconeogenesis (the process of glucose production in the liver), which decreases glucose production and increases glucose uptake into cells.

**Why Each Wrong Option is Incorrect:**

A. Insulin stimulating gluconeogenesis would increase blood glucose levels, contradicting its role in glucose homeostasis.
B. Insulin inhibiting lipolysis (breakdown of fats) is incorrect as insulin promotes glucose uptake and storage, not lipid mobilization.
C. Insulin promoting glycogen synthesis is correct, as it increases glycogen storage in the liver and muscles, helping to lower blood glucose levels. However, this option is less important compared to its effect on glycolysis and gluconeogenesis.
D. Insulin stimulating lipolysis is incorrect as mentioned above in the explanation of insulin's role in glucose homeostasis.

**Clinical Pearl:** Understanding the role of insulin in glucose homeostasis is crucial for maintaining optimal blood glucose levels and preventing complications associated with hyperglycemia or hypoglycemia.

**Correct Answer:** C. Insulin promotes glycogen synthesis.