The response to stress—be it physical or psychological, acute or chronic—involves activation of the Hypothalamic-Pituitary-Adrenal (HPA) axis. The HPA axis is part of the neuroendocrine system because it involves both neuronal and hormonal communication. Its function is to regulate homeostatic systems—metabolic, cardiovascular, and immune—providing the necessary means to respond to a stressor.

Overview

Hormones can be classified into three main types based on their chemical structures: steroids, peptides, and amines. Their actions are mediated by the specific receptors they bind to on target cells.