text: From the supine (laying down position) to the standing positions, there are several changes that occur. When supine, the blood is all at the same level as the heart, and as such, all has the same gravitational potential energy. This means the heart doesn't have to work as hard to pump it. When someone stands up, the blood "falls" down, and Baroreceptors in the aorta (among other places) cease to be stimulated. This means there will be less inhibition of the RVLM (Rostral Ventral lateral Medulla). Less inhibition means more activity, and the RVLM is part of the Vasomotor Center (along with the IVLM, CVLM and NTS) which is responsible for speeding the heart rate, raising blood pressure, and increasing blood flow. This response is momentary, as once pumping increases, flow is maintained, and the heart rate can return to normal.