Pharmacology · single question
Which molecule is responsible for the bronchoconstriction symptoms in a 12-year-old asthma patient who begins wheezing and states her chest feels tight?
Show answer and explanation
Correct answer: C. Acetylcholine
Bronchoconstriction in asthma is mediated by the parasympathetic nervous system via acetylcholine acting on M3 muscarinic receptors in bronchial smooth muscle. Acetylcholine causes bronchoconstriction and increased secretions. This is why anticholinergic drugs (ipratropium) are used in COPD/asthma. Epinephrine (beta-2 agonist effect) causes BRONCHOdilation — the opposite. Bronchodilators like albuterol work by activating beta-2 receptors to oppose acetylcholine-mediated bronchoconstriction.
- A. INCORRECT. Dopamine primarily affects cardiovascular and renal function. It does not play a significant role in bronchoconstriction.
- B. INCORRECT. Epinephrine stimulates beta-2 adrenergic receptors to cause BRONCHOdilation — it is used as TREATMENT for severe bronchospasm/anaphylaxis, not the cause of bronchoconstriction.
- C. CORRECT. Acetylcholine acting on M3 muscarinic receptors in bronchial smooth muscle causes bronchoconstriction. The parasympathetic nervous system mediates this via the vagus nerve. Anticholinergic drugs block this pathway to produce bronchodilation.
- D. INCORRECT. Serotonin can cause some bronchoconstriction in some species but is not the primary mediator of asthmatic bronchoconstriction in humans.