Chapter 12: Circulatory Systems and Fluid Transport

Circulatory Systems and Fluid Transport describes the physical properties of blood and hemolymph, including their roles in transport, immune defense, and thermoregulation. The structure of the heart is analyzed across taxa, from the two-chambered fish heart to the four-chambered mammalian heart, emphasizing how cardiac anatomy aligns with oxygen demands and systemic organization. Key physiological processes are explained, such as cardiac muscle contraction, the conduction system (including the sinoatrial and atrioventricular nodes), and the cardiac cycle. Blood pressure, resistance, and flow are introduced using principles like Poiseuille’s law and Starling forces. The chapter also addresses vascular structure and function, comparing arteries, veins, and capillaries, and showing how vessel diameter, compliance, and smooth muscle contraction regulate circulation. Hemodynamics and perfusion control are explained in the context of local and systemic regulation, with hormones and autonomic input influencing blood flow. Comparative examples from insects, amphibians, birds, and mammals illustrate circulatory diversity and adaptability. The chapter concludes by tying circulation to other systems—like respiratory and renal—and by emphasizing its central role in maintaining homeostasis.