Discuss the intricate relationship between the endocrine and nervous systems in regulating physiological processes such as stress response and metabolism. Include an analysis of the hypothalamic-pituitary-adrenal (HPA) axis, detailing the release of corticotropin-releasing hormone (CRH), adrenocorticotropic hormone (ACTH), and cortisol, and elucidate how neural signals from the brain can influence hormone secretion and vice versa.