The progression of stress, anxiety, depression

Stress, whether physiological, biological or psychological, is an organism’s response to a stressor such as an environmental condition.[1] When stressed by stimuli that alter an organism’s environment, multiple systems respond across the body.[2] In humans and most mammals, the autonomic nervous system and hypothalamic-pituitary-adrenal (HPA) axis are the two major systems that respond to stress.[3] Two well-known hormones that humans produce during stressful situations are adrenaline and cortisol.[4]

Further readings

• Read about stress in the wikipedia
• Read about anxiety in the wikipedia