Regarding the action of insulin, which of the following is true?
**Core Concept**
Insulin is a hormone secreted by the beta cells of the pancreas that plays a crucial role in glucose homeostasis. It facilitates glucose uptake in cells, thereby lowering blood glucose levels. Insulin acts by binding to its receptor on the surface of cells, triggering a cascade of intracellular signaling pathways.
**Why the Correct Answer is Right**
Insulin binds to the insulin receptor, a tyrosine kinase receptor, on the surface of cells, particularly in muscle and adipose tissue. This binding causes autophosphorylation of the receptor, which in turn activates downstream signaling pathways, including the PI3K/AKT pathway. Activation of this pathway leads to the translocation of GLUT4 glucose transporters to the cell surface, increasing glucose uptake into the cells. This results in a decrease in blood glucose levels.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because insulin does not primarily act by increasing glycogen synthesis. While insulin does stimulate glycogen synthesis, this is not its primary action.
**Option B:** This option is incorrect because insulin does not primarily act by increasing lipolysis. In fact, insulin inhibits lipolysis, promoting the storage of fatty acids as triglycerides.
**Option C:** This option is incorrect because insulin does not primarily act by increasing gluconeogenesis. Insulin actually inhibits gluconeogenesis, promoting the storage of glucose as glycogen or its utilization as energy.
**Clinical Pearl / High-Yield Fact**
It is essential to remember that insulin resistance, a condition where cells become less responsive to insulin, is a hallmark of type 2 diabetes. This can lead to hyperglycemia and increased risk of complications.
**Correct Answer:** C.