Final answer:
Beta-2 adrenergic receptors (ß2-receptors) are located in smooth muscles, particularly in the bronchi, and they mediate smooth muscle relaxation and bronchodilation when activated by catecholamines like epinephrine and norepinephrine.
Step-by-step explanation:
Beta-2 adrenergic receptors, often denoted as ß2-receptors, are a type of adrenergic receptor which can be found in various tissues throughout the body, notably in the smooth muscles of the bronchi. These receptors play a crucial role in the sympathetic nervous system, specifically in the smooth muscle relaxation process. When activated by their endogenous ligands, namely the catecholamines epinephrine and norepinephrine, the ß2-receptors trigger a series of cellular events.
These events involve coupling to a Gs protein, which ultimately leads to an increase in intracellular cyclic AMP (cAMP). The elevated cAMP levels promote relaxation of the smooth muscles, which is especially significant in the bronchi, resulting in bronchodilation. This action is essential in the management of conditions such as asthma, where bronchodilation improves air flow and eases breathing.