While I have professed the psychological effects of meditation in my previous blog posts, I now want to move onto some of the physiological effects that the practice can bring. Intuitively, common sense can already tell us what kind of consequences bringing the body to a contemplative resting state will induce. Meditation is a relaxing process, so symptoms associated with relaxation like the lowering of the heart rate, changes in metabolism, respiration and blood pressure are not surprising.
It is thought that these effects are elicited by the activation of the parasympathetic nervous system. After eating food, or having sex, the parasympathetic nervous system kicks into gear and focuses the body’s attention to things like digestion and rest. When someone begins a meditative routine we basically trick our parasympathetic nervous into action, which is why we see these symptoms like the lowering of the heart rate and heightened activity in the gut. The parasympathetic nervous systems works in contrast to the sympathetic nervous system, which is responsible for our ‘fight or flight’ response at times of high stress. So meditating can subdue the effects of the sympathetic nervous system. While it is vital to our survival, the sympathetic nervous system releases hormones into our blood stream which help us cope with high-stress situations, not the type you want floating around while you are trying to chill out.
The Science of Siddhartha: Practicing Buddhist Philosophy 