The Cardiovascular System
and the Blood
Homeostasis in the mammalian cardiovascular system depends importantly on the interactions among blood pressure, blood flow, resistance to blood flow, and other hemodynamic variables. Moreover, there are several important reflexes such as the baroreceptor reflex and the Bainbridge reflex that help maintain an equilibrium in the above hemodynamics and that try to restore homeostasis when it is disturbed.
The mammalian cardiovascular system is best understood by analyzing its component parts. In the simplest terms, these are the heart, the blood vessels, and the blood. The hearts of all mammals have four chambers: a left and a right atrium and left and right ventricles. The atria are separated by a thin wall of muscle called the interatrial septum and the ventricles are separated by the thicker interventricular septum. There are effectively two cardiovascular systems in mammals: the pulmonary and systemic (peripheral) circulatory systems. Each is composed of a pump (right or left ventricle) and a set of blood vessels. The ventricles function as the pump mechanism for generating pressure and volume work, and need to create high enough internal pressures to overcome the arterial resistance to blood flow. The ventricles must also eject a sufficient volume of blood to initiate and sustain circulation. The main differences between the two cardiovascular systems are that (1) the pulmonary circulatory system supplies blood flow only to the lungs whereas the systemic circulatory system provides blood flow to all remaining organs and tissues, and (2) the pulmonary is a low-pressure system while the systemic is a high-pressure system. The pulmonary cardiovascular system begins at the right ventricle and ends at the left atrium. The systemic or peripheral cardiovascular system begins at the left ventricle and ends at the right atrium. All other organs and tissues of the body are interposed between these two chambers. All vessel components between the two end points in either system are an integral part of that particular system.