The stress response also affects the heart, lungs, and circulation:
- As the bear comes closer, the heart rate and blood pressure increase instantaneously.
- Breathing becomes rapid, and the lungs take in more oxygen.
- The spleen discharges red and white blood cells, allowing the blood to transport more oxygen throughout the body. Blood flow may actually increase 300 - 400%, priming the muscles, lungs, and brain for added demands.
The Immune System's Response to Acute Stress
The effect of the confrontation with the bear on the immune system is similar to mobilizing a defensive line of soldiers to potentially critical areas. The steroid hormones reduce activity in parts of the immune system, so that specific infection fighters (including important white blood cells) or other immune molecules can be repositioned. These immune-boosting troops are sent to the body's front lines where injury or infection is most likely to occur, such as the skin and the lymph nodes.
The Acute Response in the Mouth and Throat
As the bear gets closer, fluids are diverted from nonessential locations, including the mouth. This causes dryness and difficulty talking. In addition, stress can cause spasms of the throat muscles, making it difficult to swallow.
The Skin's Response to Acute Stress
The stress effect moves blood flow away from the skin to support the heart and muscle tissues. This also reduces blood loss in the event that the bear causes a wound. The physical effect is cool, clammy, sweaty skin. The scalp also tightens so that the hair seems to stand up.
Metabolic Response to Acute Stress
Stress shuts down digestive activity, a nonessential body function during short-term periods of hard physical work or crisis.
The Relaxation Response: the Resolution of Acute Stress
Once the threat has passed and the effect has not been harmful (for example, the bear has not wounded the human), the stress hormones return to normal. This is known as the relaxation response. In turn, the body's systems also return to normal.
Review Date: 10/14/2010
Reviewed By: Reviewed by: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.