Chapter 12: Cardiovascular Physiology

The foundation rests on understanding blood flow dynamics, where pressure gradients and resistance determine volumetric flow according to fundamental hydraulic principles. The heart operates as two synchronized pumps separated into systemic and pulmonary circuits, with four chambers and unidirectional valves ensuring efficient propulsion. Myocardial architecture, characterized by intercalated disks and gap junctions, enables coordinated contraction essential for effective pumping. The cardiac cycle alternates between systole and diastole, encompassing distinct phases of ventricular filling, isovolumetric contraction, rapid ejection, and relaxation, each producing characteristic heart sounds reflecting valve closure events. The intrinsic conduction system, originating at the sinoatrial node and propagating through the atrioventricular node, bundle of His, and Purkinje network, coordinates electrical depolarization that triggers mechanical contraction. Pacemaker potentials and action potentials in specialized tissue generate spontaneous activity, while calcium-induced calcium release couples electrical events to myofilament shortening. Electrocardiographic patterns document these electrical events, with the P wave, QRS complex, and T wave representing sequential atrial and ventricular activity. Cardiac output, determined by stroke volume and heart rate, responds to sympathetic and parasympathetic influences, venous return mechanics following the Frank-Starling relationship, afterload conditions, and contractile state. The vasculature exhibits specialized regional functions: arteries serve as elastic reservoirs moderating pressure oscillations, arterioles regulate local blood distribution through resistance control, capillaries facilitate diffusion-based exchange governed by Starling forces balancing hydrostatic and oncotic pressures, and veins function as compliant capacitance vessels. Mean arterial pressure maintenance involves rapid baroreceptor reflexes and chemoreceptor responses, complemented by longer-term hormonal regulation including the renin-angiotensin-aldosterone system, antidiuretic hormone, and atrial natriuretic peptide. Clinical applications encompass pathophysiological states such as hypertension, hypotension, cardiogenic shock, and heart failure, illustrated through acute hemorrhage scenarios demonstrating integrated compensatory mechanisms.