Cardiac Function and Circulatory Control

The heart is a muscular pump connected to the systemic and pulmonary vascular systems. Working together, the job of the heart and vasculature is to maintain adequate circulation of blood to the organs at rest and during periods of exercise. To understand perturbations that cause symptoms and disease, it is first necessary to understand the normal anatomy and physiology of the heart, its interaction with the vascular system, and its regulation by the autonomic nervous system.

[...] A second control of the magnitude of coronary blood flow under increased workload or demand conditions is nitric oxide, which is produced by coronary vascular endothelial cells and has a direct local vasodilating effect on coronary arteries and the more distal bed. Nitric oxide is a byproduct in a number of reactions that lead to an increase in the activity of nitric oxide synthase, an enzyme that produces nitric oxide from the amino acid L-arginine. In addition to adenosine and nitric oxide, other longer-acting coronary vasodilators such bradykinin, prostaglandins, and CO2 may have a direct effect in maintaining coronary artery blood flow. [...]

[...] These curves plot end-diastolic pressure versus either cardiac output or mean arterial pressure to provide an overall characterization of LV pump function in practical terms and to demonstrate the dependence of pump function on afterload resistance and contractility. DETERMINATION OF MYOCARDIAL OXYGEN CONSUMPTION AND ENERGY METABOLISM The heart relies almost exclusively on oxidation of fatty acids and glucose as an immediate source of energy. The heart normally extracts free fatty acids preferentially from the coronary perfusion for oxidative energy production. [...]

[...] Cardiac Muscle Physiology The ability of the ventricles to generate blood flow and pressure derives from the ability of individual myocytes to shorten and generate force. Myocytes are tubular structures. During contraction, the muscles shorten and generate force along their long axis. Force production and shortening of cardiac muscle are created by regulated interactions among contractile proteins, which are assembled in an ordered and repeating structure called the sarcomere. The lateral boundaries of each sarcomere are defined on both sides by a band of structural proteins at the Z lines to which the so-called thin filaments attach. [...]