Structures that affect circulation - kidneys and blood volume and skeletal muscle pumping




• Kidneys regulate blood volume and blood osmolarity via salt and water reabsorption. • Increased reabsorption increases blood volume and venous return (and CO). • Decreased reabsorption Increases urine production, which decreases blood volume and venous return (and CO). • Systemic veins are the major blood reservoirs for the body. • Venous tone: Degree of contraction of smooth muscle in walls of the vein. • Changing venous tone changes reservoir size. • Venoconstriction: Increased venous tone that decreases venous storage and increases return (and CO). • Venodilation: Decreased venous tone that increases venous storage and decreases return (and CO). . During exercise, contraction of skeletal muscle causes veins in the muscle to be compressed. • The process milks blood toward the heart, increasing venous return. ▪ During inhalation, diaphragm moves inferiorly. ▪ Pressure in thoracic cavity drops; pressure in abdominal cavity increases. ▪ Abdominal veins are compressed, pumping more blood toward the heart, increasing venous return (and cardiac output).



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