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. For example, activation of beta-1 adrenergic receptors increases heart rate, while alpha-1 adrenergic receptors can cause blood vessels to constrict. Understanding these receptors is important for developing medications that treat conditions like asthma, hypertension, and heart failure.