Adrenergic receptors are a type of protein found on the surface of cells that respond to the neurotransmitters norepinephrine and epinephrine. These receptors play a crucial role in the body's response to stress, regulating functions such as heart rate, blood pressure, and airflow in the lungs. There are two main types: alpha and beta adrenergic receptors, each with different effects on the body. When norepinephrine or epinephrine binds to these receptors, it triggers a series of cellular responses that help the body react to various situations. For example, activation of beta receptors can increase heart rate, while alpha receptors can cause blood vessels to constrict. This complex signaling is essential for maintaining homeostasis and responding to environmental changes.