Chapter 19: Arteries and Veins

Arteries are distinguished by their thick, muscular walls composed of smooth muscle and elastic fibers that enable them to withstand high pressure and maintain vessel tone, while veins possess thinner, more compliant walls that allow them to serve as capacitance vessels storing a significant portion of blood volume. The chapter explores the hemodynamic principles governing blood flow, including the relationship between pressure gradient, resistance, and flow rate as described by Ohm's law applied to circulation, and how these variables change progressively as blood moves from large elastic arteries through muscular arteries, arterioles, and finally into capillaries. Arterial compliance and the concept of pulse pressure are introduced to explain how elastic recoil of large arteries dampens pressure oscillations and facilitates continuous blood flow during diastole. The chapter addresses mechanisms of local vascular control through autoregulation, metabolic vasodilation, and endothelial-derived relaxing factors that allow tissues to regulate their own blood supply according to metabolic demand. Venous return mechanisms are emphasized, including the skeletal muscle pump, respiratory pump, and pressure gradients that ensure adequate blood volume returns to the heart. The integration of neural control through the sympathetic nervous system, hormonal regulation via the renin-angiotensin system and vasopressin, and local paracrine signaling collectively govern vascular resistance and blood distribution. Clinical applications include understanding how disruptions in arterial compliance contribute to hypertension, how venous insufficiency affects fluid balance, and how shock states represent failures in maintaining adequate perfusion pressure and tissue oxygenation across the systemic and pulmonary circuits.