Comprehensive Osteopathic Medical Licensing Examination (COMLEX USA) Practice

What is the primary effect of the parasympathetic nervous system on arterioles?

1. Dilation

2. Constriction

3. No effect

4. Increase blood pressure

The correct answer is: Dilation

The primary effect of the parasympathetic nervous system on arterioles is dilation. This effect results from the release of neurotransmitters, primarily acetylcholine, which interacts with muscarinic receptors on the smooth muscle cells of blood vessels. Activation of these receptors leads to a signaling cascade that causes smooth muscle relaxation, resulting in the widening of the arterioles. This dilation of arterioles plays a significant role in increasing blood flow to specific regions of the body, particularly during rest and digest states, facilitating processes such as digestion and conserving energy. In contrast, the sympathetic nervous system is mainly responsible for constricting blood vessels during the fight-or-flight response, which elevates blood pressure and redirects blood flow to vital organs and muscles. It's important to note that while the parasympathetic system primarily induces dilation, certain factors can influence vascular tone and blood flow based on physiological conditions, such as the metabolic needs of tissues. However, under typical circumstances, the dilation effect is a clear primary response associated with parasympathetic activation.