Emergency Medical Technician (EMT) Intermediate Practice Exam

What type of blood vessel narrows when alpha receptors are stimulated?

1. Capillaries

2. Veins

3. Arteries

4. All blood vessels

The correct answer is: Arteries

When alpha receptors are stimulated, the primary effect is vasoconstriction, which is most prominently observed in arteries. Alpha-adrenergic receptors are found in the smooth muscle walls of these blood vessels. When stimulated by catecholamines such as norepinephrine, these receptors cause the smooth muscle to contract, resulting in narrowing of the arteries. This constriction can increase blood pressure and redirect blood flow to vital organs during stressful situations by reducing the diameter of the arterial lumen. While veins can also constrict, the response is not primarily mediated by the alpha receptors to the same extent as in arteries. Capillaries are not responsible for significant changes in vessel diameter in response to alpha stimulation as they are more involved in the exchange of gases and nutrients, and their primary regulation comes from the arterioles that feed into them. Therefore, the specificity in regards to alpha receptor stimulation aligns with the arteries as the primary vessel affected.