Final answer:
The parasympathetic division is called the "rest-and-digest" system because it promotes energy conservation and supports digestive processes by slowing down the heart rate and stimulating the digestive organs.
Step-by-step explanation:
The parasympathetic division is known as the "rest-and-digest" system because it conserves energy and promotes processes that occur during relaxed states, such as digesting food and lowering the heart rate. This division of the autonomic nervous system resets organ function after activation of the sympathetic nervous system, which is responsible for fight-or-flight responses.
The parasympathetic system achieves its restful effects by decreasing the heart rate, narrowing air passages in the lungs, and stimulating the digestive system to start working again. It does this through the release of neurotransmitters like acetylcholine, which act on the target organs to promote relaxation and digestion.