Neuroendocrine Physiology: Fundamentals and Common Syndromes

Abstract

Hormonal signaling systems are critical to basic homeostatic functions. They support the control of volume status, blood pressure, cellular metabolism, and intracellular signaling. The hypothalamic–pituitary–adrenal (HPA) axis, in particular, comprises systems to regulate sodium and water balance, steroid hormone production, glucose metabolism, and thyroid function. Each hormonal system is controlled via negative and positive feedback loops. In addition, activity levels are affected by intersystem modulation. These feedback mechanisms, with the goal of immediate homeostatsis, often cloud hormonal measurement and diagnosis in the critically ill patient. Any kind of intracranial pathology and, in particular, traumatic brain injury (TBI), stroke, or cerebral hemorrhage disequilibrate the HPA axis. This frequently results in deleterious clinical sequelae. In addition, endocrine disorders unrelated to neuropathology have significant impact on neurophysiology. Thus, dysfunction of the HPA axis must be recognized and carefully managed during the perioperative period.