Alpha-adrenergic receptors are a type of protein found on the surface of certain cells in the body. They respond to hormones like norepinephrine and epinephrine, which are involved in the body's fight-or-flight response. These receptors play a crucial role in regulating various physiological processes, including blood vessel constriction and blood pressure. There are two main subtypes of alpha-adrenergic receptors: alpha-1 and alpha-2. Alpha-1 receptors primarily cause blood vessels to constrict, increasing blood pressure, while alpha-2 receptors can inhibit the release of norepinephrine, leading to a decrease in blood pressure. Together, they help maintain balance in the body's response to stress.