HPA Axis stands for Hypothalamus-Pituitary-Adrenal Axis. It's a system in our bodies that helps us respond to stress. It's made up of three parts: the hypothalamus (a part of the brain), the pituitary gland (a small gland at the base of the brain), and the adrenal gland (a gland that sits on top of each kidney). The hypothalamus and the pituitary gland work together to control the release of adrenal hormones, like adrenaline and cortisol. These hormones help us deal with things like danger, exercise, illnesses, and changes in the environment.