Adrenergic receptors are a group of proteins located on the surface of cells that respond to the neurotransmitters norepinephrine and epinephrine. They 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 receptors, each with subtypes that have different effects on various tissues. When activated, alpha receptors generally cause blood vessels to constrict, increasing blood pressure, while beta receptors can lead to increased heart rate and relaxation of airway muscles. These receptors are important targets for medications used to treat conditions like asthma, hypertension, and heart failure.