Biological Systems MCAT Practice Exam

Which of the following is NOT a function of the sympathetic nervous system?

1. Pupil dilation

2. Decreased digestion

3. Increased urinary output

4. Stimulation of adrenal medulla

The correct answer is: Increased urinary output

The sympathetic nervous system is primarily responsible for the body's "fight or flight" response, preparing the body for action in stressful situations. This response includes several physiological changes to support immediate survival needs. Pupil dilation is a function of the sympathetic nervous system, as it allows more light into the eye, enhancing vision and awareness during stressful situations. Decreased digestion is another result of sympathetic activation; when the body is preparing for action, non-essential functions such as digestion are downregulated to allocate resources to more critical systems. Stimulation of the adrenal medulla is also part of the sympathetic response, leading to the release of adrenaline (epinephrine) and norepinephrine, which helps prepare the body for a rapid response to threats. In contrast, increased urinary output is not a function of the sympathetic nervous system. During times of stress, the body generally conserves resources, and functions like urination tend to decrease rather than increase. Therefore, the correct answer identifies increased urinary output as a function not associated with sympathetic nervous system activity.