FIGURE 30.3The appetite hormones • Ghrelin: 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.