Why Zebras Don’t Get Ulcers August 6, 2009 Abstract Why Zebras Don’t Get Ulcers by Robert M. Sapolsky, gives a description of the inner workings of the human, and animal, stress response. He talks about what physiologically happens to people when they remain in a state of stress of a long period of time. The immune response, depression, aging and death, and sexual reproduction are just some of the topics Sapolsky discusses and how stress affects each of these. Why Zebras Don’t Get Ulcers
I chose Why Zebras Don’t Get Ulcers (1994) because I was intrigued by the similarities between humans and animals in regards to their responses to acute and chronic stress. As a medical professional, I feel that I have a strong background in human physiology and therefore could relate to this book. It did not disappoint. This book is written by Robert M. Sapolsky, a professor of biological sciences, as well as neurology and neurological sciences at Stanford University. As a neuroendocrinologist, he has done extensive research in the area of hormonal response to stress and their effects on the body.
As a research associate for the National Museums of Kenya, he spends time studying baboons in their natural habitat and the stressors that they endure along with stress related illnesses that their environment may bring about. In Why Zebras Don’t Get Ulcers, Sapolsky examines the adverse effects of long-term stress and the associated physical and mental damage it can cause. During the first five chapters, Sapolsky goes into great detail, engrained with humor, about the physiological changes that happen in our bodies during periods of stress.
He explains the principles of the “fight or flight” response brought on by the body’s sympathetic nervous system, which is responsible for preparing our bodies for exertion through the release of glucocorticoids. These hormones raise our heart rate in order to increase the flow of oxygenated blood to the working muscles; gut motility decreases as blood is shunted to the vital organs; pupils dilate to increase light perception; and our airway passages dilate allowing us to increase respiration in order to bring in more oxygen which is much needed for the exertion our body is under.
All of these changes occur in just fractions of a second; however it takes longer for these effects to leave the body once the threat or stressor is removed. Sapolsky goes on to explain to the reader why other changes or responses happen during activation of the sympathetic nervous system. He humorously details why we sometimes experience loss of urinary bladder or bowel control during a stressful encounter.
If we were to get up off of our couch, walk outside the front door and come face to face with a hungry lion, then our sympathetic nervous systems will take over, secrete the stress hormones, and put our bodies through the changes I described above. In addition to preparing our bodies for fight, it will also temporarily stop the digestive process, in order to expend the body’s energy where it is needed the most. By stopping this process, the small intestines stop their contractions; however the large intestines continue their peristalsis movement in order to rid the body of excess “baggage”, or fecal matter.
It’s much easier to move quickly for humans and animals alike, whether running from a shooting down the street, or running from a hungry lion across the grasslands, when you’re not carrying a couple of extra pounds of feces. The portions of this book that were of great interest to me were when the author talks about repeated stimulations of the sympathetic nervous system and its potential harmful effects on the body over time. These stimulations don’t always have to be at the level of being face to face with the hungry lion. In our everyday modern lives, we have stressors thrust upon us, and even sometimes without our knowledge.
Our reactions to the smaller stressors in life, such as driving in traffic, arguments with spouses, raising children, stress with work for example, can cause cardiac and cardiovascular damage without us even knowing about it. Our bodies secrete stress hormones whenever we experience one of these stressful encounters, large or small. This repeated activation can, over the long term, cause irreversible damage causing the formation of atherosclerosis, which is the chronic inflammatory response in arterial walls, eventually causing blockage and reducing blood flow.
This is a particularly serious condition when it occurs in the arterial walls of the small coronary arteries which feed oxygen to the heart muscle. In a typical fight or flight response, these coronary arteries will dilate in order to increase their capacity for delivering oxygen-rich blood to the heart, which is now beating faster to provide blood to the muscles. Sapolsky tells us that continued stress responses will decrease the vessel’s ability to dilate and may in fact constrict, therefore reducing oxygenated blood to reach the cardiac tissue when it needs it the most.
The chest pain that these people feel during stressful times unfortunately may be the first and only indicator of cardiac disease. This damage is not just limited to the cardiovascular system. With enough stress, humans are at a higher risk for developing adult-onset diabetes. This is due to the body releasing glucose and fatty acids into the bloodstream during stress, again in order to feed the exerting muscles. At the same time, the body tends to block insulin production, and we remember from basic physiology that insulin is the key hormone that allows glucose to enter the cells.
Without insulin there to make this happen, excess glucose remains in the blood if it’s not used by the muscles. Continued stress responses over time can eventually cause the uptake of glucose into the cells to be hindered, thereby creating a diabetic condition. Sapolsky goes on to explain how stress in our lives can also lead to loss of libido and reproduction. During periods of stress, males can see a decrease in circulating testosterone due to a release of specific hormones in the brain which basically shut down the activity of the testes, which are responsible for testosterone release.
On the female side, the author tells us that studies have shown how stress suppresses estrogen production, which in turn disrupts sexual behavior in women. (Sapolsky, 1994. p. 124) Another interesting part of this book, talks about the decreased immune response during times of stress. Hans Selye, one of the godfathers of stress physiology, discovered the first evidence of stress-induced immunosuppression back in the 1930s. Selye learned that the same glucocorticoids that are responsible for sympathetic response, was also a large contributor in immune system suppression.
Glucocorticoids stop the formation of lymphocytes as well as inhibit the release of interleukins and interferons which make already circulating lymphocytes less responsive to infections. Sapolsky hypothesized why evolution would create this process from happening. He wanted to know why the immune system is disabled during periods of stress. As he states in this book, it appears that no one knows just yet why this makes sense. In the later chapters, Sapolsky talks about the effects of stress on aged organisms.
Compared to younger generations, the elderly function just the same as long as they are not stressed. Once a stressor is introduced, the elderly may have numerous problems coping with that stress. There may be a lack of a stress response, or a decreased sympathetic response because the heart itself and the blood vessels have lost their elasticity which allow them to dilate and constrict, and therefore may not be able to respond appropriately to physiological changes. Another problem may be that they have too much of a stress response.
It will take longer for hormone levels to return to their pre-stress levels and return to baseline. The author concludes this section by revealing that in more than a dozen species, excess glucocorticoid levels is the cause of death during aging. (Sapolsky, 1994, p. 237) Overall I was very pleased with this book. I was very surprised at the immense detail Sapolsky went into in describing the hormonal response during stress. His background and experience as a neuroendocrinologist was very apparent in his writing.
For someone without formal knowledge of human physiology, I could see this being a difficult read. He does however take the time to explain these processes with his humorous tone, and this makes it a much more enjoyable read. As a result of reading this book, I am committing myself to the following changes. I always understood the adverse effects that stress had on the body, but I received somewhat of a wake-up call when I read about how the continued release of stress hormones over the years can have such a damaging effect on the heart.
I will do my best to avoid being upset by the little things in life and take the stress relief measures that I have learned and apply them to my own life so that I can prevent cardiac problems, diabetes and other stress-induced diseases. I may not be under the threat of being gored by an elephant or sized up by a hungry lion each day, but I can still take Sapolsky’s lessons and use that knowledge to better my life by improving how I perceive the stressors I encounter. References Sapolsky, R. (1994). Why Zebras Don’t Get Ulcers. New York, New York. W. H. Freeman and Company
