A new low-budget private health insurance company has just started up which sends its patients to second-year Physiology students for diagnosis and treatment. You work at their clinic called “University Health Services” on the weekends. (Note these questions aren’t necessarily true clinical issues or treatments, but instead designed to test your understanding of the Physiological concepts).
For the following conditions, select the most appropriate treatment option.

Reduced blood flow to the heart, liver and brain during periods of fear or arousal.

Question

A new low-budget private health insurance company has just started up which sends its patients to second-year Physiology students for diagnosis and treatment. You work at their clinic called “University Health Services” on the weekends. (Note these questions aren’t necessarily true clinical issues or treatments, but instead designed to test your understanding of the Physiological concepts).
For the following conditions, select the most appropriate treatment option.

Reduced blood flow to the heart, liver and brain during periods of fear or arousal.

BlackTom AI · Accepted Answer

β2-adrenergic receptor agonists cause vascular smooth muscle relaxation via Gs-mediated increases in cAMP, producing vasodilation in vascular beds (including coronary, hepatic and cerebral microvasculature) and thereby increasing blood flow to heart, liver and brain.

1) Relevant knowledge points and concepts
- Sympathetic adrenergic signaling: α1 receptors on vascular smooth muscle cause vasoconstriction (via Gq → IP3/Ca2+), whereas β2 receptors cause vasodilation (via Gs → ↑cAMP → smooth muscle relaxation).
- Distribution: Coronary, hepatic and many cerebral vessels express β2 receptors; activating these dilates those beds and raises local perfusion.
- Physiologic response to fear/arousal: catecholamine surges can increase α1-mediated vasoconstriction in some beds; if net effect is reduced perfusion to heart, liver, brain, a targeted β2 agonist will reverse constriction locally.

2) Step-by-step reasoning
- Problem: reduced blood flow to heart, liver and brain during fear/arousal implies excessive vasoconstriction of those vascular beds.
- Goal: selectively dilate those vessels to restore perfusion without undesired systemic effects.
- Mechanism choice: stimulating β2 receptors on vascular smooth muscle increases cAMP and relaxes the muscle, increasing lumen diameter and flow (Poiseuille’s principle: flow ∝ radius^4), so small increases in vessel radius produce large increases in flow.

3) Calculations/intermediate steps
- No numerical calculation required; physiologic principle: flow is highly sensitive to radius; β2-mediated relaxation increases radius → large increase in flow.

4) Why the correct answer is correct
- A β2-receptor agonist directly promotes vasodilation where β2 receptors are present (coronary, hepatic, cerebral vessels), reversing sympathetic-induced constriction and restoring perfusion.

5) Why other plausible options are incorrect
- α1 agonists would worsen vasoconstriction. α1 antagonists (e.g., prazosin) could dilate but are less targeted and risk systemic hypotension. β1 agonists increase heart contractility (and O2 demand) but do not dilate the vascular beds needed. Nonselective catecholamines (e.g., epinephrine) have mixed effects and may not selectively improve these beds.

6) Conclusion
This physiological reasoning supports the provided correct choice: g. β2-receptor agonist.

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