Final answer:
Jenny's body is maintaining homeostasis through sweating, which is regulated by the effector sweat glands as part of the body's negative feedback loop.
Step-by-step explanation:
Jenny is running for more than an hour on a pleasant sunny morning. Her body is sweating to maintain homeostasis, which is caused by the action of a/an effector. In the process that maintains homeostasis, the body temperature regulation is a key example of a negative feedback loop.
When Jenny's body temperature rises, sensors within her body detect the increase in temperature and send a signal to the control center, typically the hypothalamus in the brain, which then signals the effectors to initiate sweating. The sweat glands are the effectors in this scenario; they release sweat, which cools the body through evaporation and helps return the body temperature to its set point, thereby maintaining homeostasis.