The parasympathetic nervous system is a part of the autonomic nervous system, which controls involuntary bodily functions. It is often referred to as the "rest and digest" system because it helps the body relax and conserve energy after stressful situations. This system promotes activities such as digestion, slowing the heart rate, and lowering blood pressure. When activated, the parasympathetic system releases neurotransmitters like acetylcholine, which signal various organs to function optimally. For example, it stimulates the salivary glands to produce saliva and encourages the stomach to secrete digestive enzymes, facilitating the process of digestion and nutrient absorption.