Final answer:
Beta-2 adrenergic receptors are located in the smooth muscles, especially in the bronchi, and are responsible for smooth muscle relaxation, which is crucial for air passage during respiration.
Step-by-step explanation:
Where are Beta-2 Adrenergic Receptors Located and What Do They Do?
The beta-2 adrenergic receptors, also known as B2 receptors, are primarily found in smooth muscles of the body including the muscles in the bronchi. They play a crucial role in smooth muscle relaxation, particularly in the bronchi, which is important for managing the airway diameter and thus affects breathing.
When epinephrine binds to these receptors, a G-protein is activated which in turn activates adenylyl cyclase, converting ATP to cAMP. The increased levels of cAMP function as a second messenger, leading to the relaxation of smooth muscle tissue. This mechanism is particularly significant during an asthma attack when it's necessary to reduce bronchoconstriction and ease breathing.
Additionally, the beta-2 receptors can be found in other parts of the body and are involved in functions such as vasodilation of blood vessels and glycogenolysis in the liver. They are activated by epinephrine and norepinephrine, both originating from the adrenal glands, and their distribution in the body varies dependant on the function they mediate.