Beta-adrenergic receptors are a type of protein found on the surface of cells that respond to hormones like epinephrine and norepinephrine. These receptors play a crucial role in the body's response to stress, helping to regulate functions such as heart rate, blood pressure, and airflow in the lungs. There are three main subtypes of beta-adrenergic receptors: beta-1, beta-2, and beta-3. Each subtype has different functions and is located in various tissues throughout the body. For example, beta-1 receptors are primarily found in the heart, while beta-2 receptors are mainly located in the lungs and blood vessels.