RT Book, Section A1 Jameson, J. Larry A2 Loscalzo, Joseph A2 Fauci, Anthony A2 Kasper, Dennis A2 Hauser, Stephen A2 Longo, Dan A2 Jameson, J. Larry SR Print(0) ID 1190523770 T1 Mechanisms of Hormone Action T2 Harrison's Principles of Internal Medicine, 21e YR 2022 FD 2022 PB McGraw-Hill Education PP New York, NY SN 9781264268504 LK accessmedicine.mhmedical.com/content.aspx?aid=1190523770 RD 2024/11/03 AB Hormones function to integrate physiologic systems in the body. The endocrine system, composed of various glands and the hormones they produce, interacts with essentially every organ to regulate growth, metabolism, homeostasis, and reproduction. Because hormones circulate and act via receptors in target tissues, they serve to coordinate physiologic responses to external or internal cues. For example, the light-dark cycle, sensed through the visual system, modulates hypothalamic corticotropin-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.