**Question:** Not done by insulin

**Core Concept:** Insulin is a hormone produced by the beta cells of the pancreas that plays a crucial role in regulating blood glucose levels by stimulating cellular uptake of glucose and inhibiting gluconeogenesis and glycogenolysis in hepatocytes.

**Why the Correct Answer is Right:** Insulin is responsible for lowering blood glucose levels by facilitating glucose uptake into cells, particularly in the liver, muscle, and adipose tissues. Insulin does not directly inhibit gluconeogenesis, the process of glucose production in the liver, nor glycogenolysis, the breakdown of glycogen into glucose in the liver and muscles.

**Why Each Wrong Option is Incorrect:**

A. Insulin does stimulate glucose uptake into hepatocytes but does not directly inhibit gluconeogenesis, making it incorrect.
B. Similar to option A, insulin promotes glucose uptake but not inhibition of gluconeogenesis.
C. Insulin does stimulate glucose uptake but does not directly inhibit glycogenolysis, making it incorrect.
D. Insulin enhances glucose uptake, but it does not directly inhibit gluconeogenesis or glycogenolysis, rendering it incorrect.

**Clinical Pearl / High-Yield Fact:** Understanding the specific actions of insulin and its role in glucose regulation helps prevent confusion and misconceptions regarding insulin's effects on glucose homeostasis.

**Correct Answer:** D. Insulin enhances glucose uptake, but it does not directly inhibit gluconeogenesis or glycogenolysis, making option D the correct answer. Insulin's primary action is to enhance glucose uptake and utilization in target cells, such as hepatocytes and muscle cells, thereby lowering blood glucose levels indirectly. Its effects on glucose homeostasis involve promoting glucose uptake, inhibiting gluconeogenesis, and stimulating glycogen synthesis in the liver.