Comprehensive Osteopathic Medical Licensing Examination (COMLEX USA) Practice

What effect does the sympathetic nervous system have on general arterioles?

1. Dilation

2. Constriction

3. Increased blood flow

4. No effect

The correct answer is: Constriction

The sympathetic nervous system primarily exerts a constrictive effect on general arterioles. This is achieved through the release of norepinephrine, which binds to alpha-1 adrenergic receptors on smooth muscle cells of the arterioles. When these receptors are activated, smooth muscle contraction occurs, leading to vasoconstriction. This process reduces the diameter of the arterioles, which in turn increases vascular resistance and can elevate blood pressure. In the context of the body's "fight or flight" response, the constriction of arterioles serves to prioritize blood flow to vital organs, such as the heart and muscles, while reducing blood supply to less critical areas. This physiological mechanism is essential for preparing the body to respond to stress or danger by ensuring that key systems receive adequate oxygen and nutrients. While the sympathetic nervous system can also influence blood flow through vasodilation in specific vascular beds (like skeletal muscles during exercise), the general effect on arterioles throughout the body is one of constriction. Other options, such as dilation or increased blood flow, do not accurately reflect the predominant action of the sympathetic nervous system on arterioles in most situations.