Final answer:
Beta-1 receptors are mainly located in the heart, enabling increased cardiac output when stimulated, while beta-2 receptors are found in the lungs and other smooth muscles, causing relaxation upon stimulation.
Step-by-step explanation:
Beta-1 receptors are primarily located in the heart; whereas beta-2 receptors are primarily located in the lungs and smooth muscles of various organs. The binding of catecholamines such as adrenaline (epinephrine) and noradrenaline (norepinephrine) to these adrenergic receptors triggers the fight-or-flight response in the body.
Beta-1 adrenergic receptors when activated, lead to an increase in cardiac output by raising the heart rate and increasing the volume expelled with each heartbeat. On the other hand, beta-2 adrenergic receptors, upon activation result in the relaxation of smooth muscle such as that found in the bronchi of the lungs. Adrenergic receptors, including both alpha and beta receptors, are all G protein-coupled receptors. Beta receptors are linked to the Gs protein and when activated, they increase intracellular cAMP activity. This leads to various responses such as heart muscle contraction in the case of beta-1 and smooth muscle relaxation in the case of beta-2 receptors.