Robert Sapolsky’s Why Zebras Don’t Get Ulcers hooked me from the title. At first read the title may sound irreverent but it actually is a true statement. I took copious notes based on his explanation of the science of stress and his suggestions, at the end, for managing stress. I’ve written about the nervous system in prior blog posts, but this is the first time the physiology has made its way front and center in my blogging and understanding.
As Sapolsky notes, our sympathetic and parasympathetic nervous systems work in opposition to one another. The sympathetic system turns on with excitement or alarm, causing the release of epinephrine (adrenaline) from the adrenal glands and norepinephrine (noradrenaline) from all other glands. This, in turn, speeds up the heart and sends blood to the muscles, allowing for a fast and efficient response to whatever caused the initial response. When the mellow parasympathetic system is activated via the vagus nerve, it slows down the heart and diverts blood from the muscles, making it possible to calm, slow down, or sleep. Each of these nervous system responses causes different, opposing reactions within the body. What intrigued me, and to the best of my recollection I have not written about, is the actual science of what happens in the body when it undergoes a stress response.
The Physiologic Details, in other words, the chemical flow
Within 15 seconds of being triggered by a stressor, the Hypothalamus releases CRH (corticotropin releasing hormone) which turns on the sympathetic nervous system and also suppresses appetite. CRH signals the Pituitary to release ACTH (adrenocorticotropic hormone or, simply, corticotropin). The pituitary regulates peripheral glands, and within a few minutes ACTH reaches the adrenal gland. The adrenal gland, in turn, releases glucocorticoid, which also stimulates appetite for starch, sugar and fat, those being energy sources which would be necessary if you needed to move your muscles and get out of a situation quickly! The adrenal glands also release the epinephrine and norepinephrine noted in the paragraph above.
The adrenals hand off to the pancreas, which releases glucagon, causing increases in the levels of glucose (glucose being sugar). The pituitary and brain release endorphins and enkephalins to blunt pain perception. The pituitary also releases vasopressin, which impacts cardiovascular response.
You might begin to see a cascading chemical soup that, depending upon the magnitude of the stressor, can begin to saturate the body. You might also wonder why the body might both suppress or stimulate appetite from the same series of signals. Turns out that the type of stressor, its duration and the time it takes to recover from the stressor all determine if appetite is suppressed or stimulated. According to Sapolsky, two-thirds of people eat more when under stress (hyperphagic) and one-third eat less (hypophagic). (I am of the first type and my husband is of the second. The good news is, once you know your tendencies you can work to adjust accordingly.)
Stress and the Heart
The heart’s sole job is to pump blood thru the “hoses” – the veins and arteries snaking thru the body. Blood pressure is the force with which the blood flows thru these “hoses.” If you’ve had your blood pressure measured in a doctor’s office, you likely know there are two numbers generated. Systolic pressure is the upper number and is the force with which blood leaves the heart thru the arteries. Diastolic pressure is the lower number and is the force with which blood returns to the heart thru the veins.
Ideally, to keep a healthy heart, the hoses need to be free of obstructions and the blood pressure needs to be able to return to a healthy level after engaging in a stress response. What makes the difference is whether the body is undergoing an acute response to stress (quick and over soon) or a chronic response (ongoing, which provides insufficient opportunity to recalibrate at healthy levels).
Our breathing has an effect on our heart. Generally, inhaling turns on the sympathetic nervous system, allowing it to energize, and exhaling turns on the parasympathetic, sending the signal to calm. The interplay of the inhales and exhales is what can stimulate the relaxation response (more about the response here and here).
The length of time between heartbeats is HRV (heart rate variability). A higher HRV signifies short interbeat intervals during inhale and long interbeat intervals during exhale. A minimal HRV means it is difficult to turn on the parasympathetic and turn off the sympathetic. To quote what I wrote about HRV in a prior post:
Typically, during an INhale the message is to speed up the heart rate, which in turn activates the sympathetic nervous system. This automatically kicks in when we feel stress. During an EXhale the heart rate slows and that, in turn, activates the parasympathetic nervous system. The other piece of this process is HRV (heart rate variability). Whereas heart rate refers to the number of beats per minute, and can be measured by taking a pulse, heart rate variability is the time between each heart beat and requires an EKG machine for measurement. The higher HRV, the more parasympathetic activity there is, which bodes well for long-term health. Curiously, this is a measurement that is rarely provided during an annual physical!
A Visual Summary
I have taken numerous yoga trainings with Jillian Pransky and in just about every training she has shared imagery that distills what happens in the body when the stress response is activated. From Jillian’s imagery I created the graphic below, which also includes the Relaxation Response.
Imagine a house with six rooms: reproduction, immunity, growth and repair, elimination, digestion, and a safe room. As a result of the FIGHT or FLIGHT response being activated, resources are channeled via a hormonal response to the safe room and shut off to the other rooms. In the safe room the brain is primed to isolate, build a wall, and separate and protect.
With activation of the REST and DIGEST response, resources are channeled via a hormonal response to the five main rooms and shut off to the safe room. When these other rooms are functioning the brain is primed to “tend and befriend.” The LARLAR at the upper left is Jillian’s acronym for how to manage the body’s response to stress and return to homeostasis: Land (the body internally and on the ground), Arrive (with your breath, guiding it deeper), Relax (arriving with a deeper breath will stimulate relaxation), Listen to yourself, Allow space for what you hear, Repeat because “the LARLAR is never done.”