FIGURE 9.7 The appetite hormonesGhrelin: Hormone secreted by empty stomach; sends “I’m hungry” signals to the brain. Insulin: Hormone secreted by pancreas; controls blood glucose. Leptin: Protein hormone secreted by fat cells; when abundant, causes brain to increase metabolism and decrease hunger. Orexin: Hunger-triggering hormone secreted by hypothalamus. PYY: Digestive tract hormone; sends “I’m not hungry” signals to the brain.