Breathing becomes rapid and shallow. Adrenaline and other hormones are released into the blood. The liver releases stored sugar into the blood to meet the increased needs for survival. Muscles tense for movement, either for flight or protective actions. Blood flow is greatly constricted to the digestive organs.
Blood flow increases to the brain and major muscles.
Blood flow is constricted to the extremities. The body perspires to cool itself, since increased metabolism generates more heat. Your stress response is appropriate if you are confronted by some threat to your life. But most often in our society stress is triggered by a situation which is stressful but not life threatening. Your consciousness has developed to the extent that emotions, ideas, memories and expectations can trigger stress.