Alpha-adrenergic receptors are a type of protein found on the surface of certain cells in the body. They play a crucial role in the sympathetic nervous system, which is responsible for the body's "fight or flight" response. When activated by hormones like norepinephrine and epinephrine, these receptors help regulate various functions, including blood vessel constriction and increased heart rate. There are two main subtypes of alpha-adrenergic receptors: alpha-1 and alpha-2. Alpha-1 receptors primarily cause blood vessels to constrict, leading to increased blood pressure, while alpha-2 receptors can inhibit the release of norepinephrine, providing a calming effect. Together, they help maintain balance in the body's response to stress.