The mean arterial pressure is the average blood pressure within the arterial walls of a persons circulatory system. Organs must receive blood to deliver nutrients and oxygen and also to pick up carbon dioxide and other waste products that are produced as a byproduct of cellular respiration. Organs can continue to function on a mean arterial pressure as low as 60 millimeters of mercury. The average mean arterial pressure is somewhere between 70 to 110 millimeters of mercury. The short-term response by the body when experiencing a drop in mean arterial pressure would be an increased heart rate, in an effort to rebuild the drop in pressure. Blood vessels could also constrict, causing a rise in blood pressure. The long-term responses of the body could be increased levels of epinephrine, which would increase the heart rate, and other hormones which would cause the blood pressure to increase.