What is the hormone responsible for stimulating appetite?

Ghrelin is the hormone that plays a significant role in stimulating appetite. It is often referred to as the "hunger hormone" because its levels rise before meals and fall after eating. Produced predominantly in the stomach, ghrelin signals the brain to increase food intake and promote fat storage. This hormone acts on the hypothalamus, the area of the brain involved in regulating hunger and energy balance, making it a crucial player in appetite regulation.

Insulin, while important for glucose metabolism and storage, primarily functions to lower blood sugar levels and does not have a direct stimulatory effect on appetite. Leptin, produced by adipose (fat) tissue, is involved in signaling satiety; it informs the brain about energy stores, leading to a reduction in appetite. Glucagon is primarily known for its role in increasing blood sugar levels by promoting the release of glucose from the liver, and it does not stimulate appetite directly. Therefore, ghrelin's unique role in appetite stimulation distinguishes it as the correct answer.