RT Book, Section A1 Jameson, J. Larry A2 Jameson, J. Larry A2 Fauci, Anthony S. A2 Kasper, Dennis L. A2 Hauser, Stephen L. A2 Longo, Dan L. A2 Loscalzo, Joseph SR Print(0) ID 1155954048 T1 Mechanisms of Hormone Action T2 Harrison's Principles of Internal Medicine, 20e YR 2018 FD 2018 PB McGraw-Hill Education PP New York, NY SN 9781259644016 LK accessmedicine.mhmedical.com/content.aspx?aid=1155954048 RD 2024/03/28 AB Hormones function as a communication system within the body. The endocrine system, composed of various glands and the hormones they produce, interacts with essentially all other physiologic systems to regulate growth, metabolism, homeostasis, and reproduction. Because hormones circulate and act via receptors in target tissues, they serve to integrate physiologic responses to external or internal cues. For example, the light-dark cycle, sensed through the visual system, modulates hypothalamic corticotopin-releasing hormone (CRH), which increases pituitary adrenocorticotropin hormone (ACTH) production, leading to increased adrenal cortisol production before the time of waking in the morning. Increased cortisol, in turn, circulates throughout the body, acting via the nuclear glucocorticoid receptor, to activate numerous genetic programs that influence metabolism, the cardiovascular system, behavior, and the immune system. This chapter provides an overview of the different types of hormones and how they function at the cellular level to control myriad physiologic processes.