Chapter 14: Cardiovascular Physiology

Cardiovascular Physiology establishes the fundamental physics of hemodynamics, explaining that blood flow is directly proportional to pressure gradients and inversely proportional to resistance, with vessel radius acting as the primary determinant of resistance as described by Poiseuille’s law. The anatomical review covers the heart's four chambers, the interventricular septum, and the connective tissue rings that support the atrioventricular (tricuspid and mitral) and semilunar (aortic and pulmonary) valves, which mechanically prevent backflow. At the cellular level, the text distinguishes between myocardial contractile cells, which utilize excitation-contraction coupling involving calcium-induced calcium release and exhibit a long refractory period to prevent tetanus, and autorhythmic pacemaker cells, which rely on unique If channels to generate spontaneous depolarizations. The sequence of electrical conduction is mapped from the sinoatrial node through the internodal pathways, the atrioventricular node (where conduction delays occur), the AV bundle, and finally to the Purkinje fibers, coordinating atrial and ventricular contraction. These electrical events are correlated with the P wave, QRS complex, and T wave of an electrocardiogram, which serves as a vital clinical tool for diagnosing arrhythmias and conduction blocks. The mechanical progression of the cardiac cycle is detailed through phases such as isovolumic ventricular contraction, ventricular ejection, and isovolumic relaxation, all of which are visualized through pressure-volume loops and the Wiggers diagram. The summary concludes by breaking down the regulation of cardiac output, defined as heart rate multiplied by stroke volume, examining how the sympathetic and parasympathetic divisions control rate and how stroke volume is modulated by length-tension relationships known as the Frank-Starling law of the heart, contractility changes via inotropic agents, and the resistance of afterload.