Alpha-1 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 or epinephrine, these receptors cause various physiological effects, such as vasoconstriction, increased blood pressure, and pupil dilation. These receptors are primarily located in smooth muscle tissues, including blood vessels and the urinary tract. Their activation leads to muscle contraction, which can affect blood flow and organ function. Understanding alpha-1 adrenergic receptors is important for developing medications that target conditions like hypertension and certain urinary disorders.