How does physical activity effect our hormone?

Referring to following statements, I would like to know on why physical activity can alleviate stress, and how does physical activity effect our hormone?

Does anyone have any suggestions?
Thanks in advance for any suggestions

"The hypothalamus, pituitary gland, and adrenal glands make up the HPA axis, which plays a pivotal role in triggering the stress response. By releasing certain chemicals, such as adrenocorticotropic hormone (ACTH) and cortisol, the HPA axis rouses the body for action when it’s faced with a stressor."

"Exercise. Physical activity alleviates stress and reduces your risk of becoming depressed."
Ref : http://www.patienteducationcenter.org/articles/hearts-minds-how-stress-negative-emotions-affect-heart