Control Mechanisms

Abstract

The initiation of the heart beat and nervous control over its regularity, frequency and amplitude have been dealt with in chapter 6. These parameters are of course important in respiration, since the speed with which oxygen reaches the tissues and with which carbon dioxide is removed from them generally depend on the efficiency of the circulatory system. Thus, not only is some efficient pumping organ, the heart, necessary to meet the respiratory demands of the animal, but the closer the immediate requirements can be reflected by alterations in the velocity of blood flow, the more independent from the environment can the animal become, with the proviso that a very high rate of heart beat is clearly undesirable because of the energy required to maintain it.