The system that regulates functions rapidly but has short-lived effects is the nervous system.

Here's why:

* Speed: The nervous system uses electrical signals that travel very quickly along nerves, allowing for rapid responses to stimuli.

* Short-lived effects: The effects of nerve impulses are typically short-lived because neurotransmitters, the chemical messengers of the nervous system, are quickly broken down or reabsorbed. This allows for precise control and rapid adjustments to changing conditions.

In contrast, the endocrine system, which uses hormones for communication, is much slower but has longer-lasting effects.

Let me know if you'd like more information about the nervous system or the endocrine system!