Why is insulin referred to as the key in glucose metabolism?

Insulin is often referred to as the "key" in glucose metabolism because it facilitates the entry of glucose (sugar) into the body's cells. When insulin is released into the bloodstream, it binds to specific receptors on the surface of cells, effectively "unlocking" them. This process allows glucose to enter the cells, where it can be used as a source of energy for cellular functions.

This role is crucial for maintaining normal blood sugar levels and providing energy to various tissues, especially muscle and fat cells. Without insulin, glucose struggles to enter the cells, leading to elevated blood sugar levels and potentially resulting in conditions such as diabetes.

In contrast, the other answer choices do not accurately describe the primary function of insulin in glucose metabolism. While oxygen is vital for cellular respiration, it is not directly affected by insulin's action. Protein synthesis is influenced by insulin but is not its primary role concerning glucose metabolism. Blood pressure regulation is not a function of insulin at all.