Final answer:
Beta agonists facilitate bronchodilation by stimulating beta-2 adrenergic receptors, which increase cAMP levels and activate PKA, resulting in smooth muscle relaxation.
Step-by-step explanation:
Beta agonists cause bronchodilation by activating beta-2 adrenergic receptors on the bronchial smooth muscle, which results in smooth muscle relaxation. This activation occurs via a mechanism that involves Gs proteins leading to the conversion of ATP to cyclic AMP (cAMP) by adenyl cyclase. The increase in cAMP activates protein kinase A (PKA), which in turn phosphorylates target proteins, eventually causing muscle relaxation and bronchodilation.