The image above to the left shows a detail of runners on a Greek amphora painted in the sixth century B.C. Athletic feats, as well as others as seemingly simple as the maintenance of blood-glucose levels, require elaborate metabolic integration. The representation at the right shows the organs that have essential roles in the metabolic integration that regulates blood-glucose levels during exercise and at rest. Insulin and leptin (secreted by adipocytes) are two of the hormones that modulate the metabolic pathways of organs throughout the body such that adequate energy is available to meet the demands of living.