Final answer:
Ipratropium treats COPD by competitively inhibiting cholinergic M3 receptors, causing bronchodilation and relieving respiratory symptoms.
Step-by-step explanation:
In patients with chronic obstructive pulmonary disease (COPD), ipratropium acts by A. Competitive inhibition of cholinergic M3 receptors. Ipratropium is a bronchodilator that exhibits its effects by blocking muscarinic cholinergic receptors in the lungs. This blockage prevents acetylcholine from binding to these receptors, inhibiting the parasympathetic nervous system effects that would normally result in bronchoconstriction. Since muscarinic M3 receptors are responsible for bronchoconstriction in the lungs, the competitive inhibition by ipratropium leads to relaxation of the airway smooth muscles, thereby helping to relieve respiratory symptoms associated with COPD.