Biological Systems MCAT Practice Exam 2026 – The Comprehensive All-in-One Guide for Exam Success!

The parasympathetic nervous system is primarily responsible for promoting "rest and digest" functions, which are essential for conserving energy and maintaining homeostasis in the body. When the parasympathetic system is activated, it leads to several physiological responses that facilitate digestion and relaxation. For instance, it enhances gastrointestinal activity by stimulating peristalsis and the secretion of digestive enzymes, allowing for efficient processing of food. Additionally, it promotes salivation and stimulates the production of insulin to help regulate blood sugar levels after eating.

This system counterbalances the more stimulating effects of the sympathetic nervous system, which is associated with the "fight or flight" response characterized by heightened alertness, increased heart rate, and elevated blood pressure. The parasympathetic system, on the other hand, works to lower heart rate, decrease blood pressure, and promote overall relaxation, reinforcing its role in "rest and digest" activities. Therefore, the correct answer accurately reflects the primary functions of the parasympathetic nervous system.