What is a major action of Alpha 1 receptors?

Alpha 1 receptors are primarily associated with the sympathetic nervous system and are responsible for various physiological effects when stimulated. A major action of these receptors is mydriasis, which refers to the dilation of the pupils, and vasoconstriction, the narrowing of blood vessels. When alpha 1 receptors are activated, they cause smooth muscle contraction in the vascular system, leading to increased peripheral resistance and blood pressure. This mechanism plays a crucial role in the body's response to stress or injury, allowing for the prioritization of blood flow to vital organs.

While other options mention different actions, they do not accurately reflect the primary role of alpha 1 receptors. For instance, bronchodilation and vasodilation are mainly associated with beta receptors, while decreased sympathetic outflow does not align with the stimulating action that alpha 1 receptors exert in response to stress. Thus, understanding the specific physiological impact of alpha 1 receptor activation clarifies why mydriasis and vasoconstriction are significant actions attributed to these receptors.