Final answer:
Jen's "runner's high" is likely due to high levels of endorphins and endocannabinoids, which are neurotransmitters that create feelings of well-being. So the correct answer is option (A).
Step-by-step explanation:
Jen's feeling of elation and the so-called "runner's high" after completing a marathon may be attributed to the abnormally high levels of neurochemicals known as endocannabinoids and endorphins in her brain. These chemicals act as neurotransmitters, which are released during vigorous activities such as running. Endorphins function as natural pain relievers, producing feelings of euphoria, while endocannabinoids play a role in the positive effects of exercise on mood and the sensation of the "runner's high." Therefore, the correct answer is a) neurotransmitters.
Specifically, the release of neurotransmitters called endorphins contributes to the feelings of euphoria and well-being commonly described as a "runner's high." Endorphins are natural chemicals produced by the body in response to stress and pain, and they act as neurotransmitters in the brain, binding to opioid receptors to reduce the perception of pain and promote a positive mood.
While other options (b) enzymes, (c) hormones, and (d) glucose play important roles in various physiological processes, the immediate cause of the mood-enhancing effects after strenuous exercise is often attributed to the release of endorphins, which act as neurotransmitters in the brain.