Structures that affect circulation - kidneys, blood volume and venous tone Date Uploaded: 01/26/2020• 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). You must login to add videos to your playlists.