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V E N O U S RETURN

V E N O U S RETURN. Venous return. Volume of blood entering each atrium in each minute Factors enhancing VR sympathetically induced venous vasoconstriction Sk. Muscle activity Effect of venous valves Respiratory activity Cardiac suction effect. Venous return.

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V E N O U S RETURN

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  1. V E N O U S RETURN

  2. Venous return Volume of blood entering each atrium in each minute Factors enhancing VR • sympathetically induced venous vasoconstriction • Sk. Muscle activity • Effect of venous valves • Respiratory activity • Cardiac suction effect

  3. Venous return Sympathetically induced venous vasoconstriction • Veins are not very muscular • Little inherent tone • Abundant SN fiber supply SN stimulation _________ Vasoconstriction ___________ Elevates venous pressure _______ Increase pressure gradient from veins to RA

  4. Venous return Sympathetically induced venous vasoconstriction • Decreases venous capacity ______ • Less blood remains in veins ___________ • Continuous flow towards the heart ___ • Increased EDV ____ • Increased CO (frank starling mechanism).

  5. Venous return Sk. Muscle activity Compensatory measures to counteract G R A V I T Y • Sympathetically induced venous vasoconstriction • SM pump “interrupts” the column of blood by emptying vein segments intermittently

  6. Venous return Effect of venous valve • Large veins are equipped with one-way valves at 2-4cm interval

  7. Venous return • Respiratory pump • An externally applied pressure gradient exists b/w the lower veins (at atmospheric pressure) and • the chest veins (at 5mm Hg less than atmospheric pressure)

  8. Venous return Cardiac suction effect • During ventricular contraction , AV valves are drawn downwards enlarging the atrial cavities • Atrial pressure transiently drops <0 mm of Hg • Increasing vein –to-atria pressure gradient • during ventricular relaxation transient –ve pressure increases vein – to - atria – to - ventricle gradient

  9. CV changes during exercise • HR () • Increased SN activity &dec. PSN activity • VR () • SN induced venous vasoconstriction • Sk. M pump • SV () • Inc. VR (F/ S mechanism) • Sympathetically induced inc. in contractibility

  10. CV changes during exercise • Blood flow to muscle & heart muscle() • Locally controlled arteriolar vasodilatation • Blood flow to brain (unchanged) • S stimulation has no effect on brain arterioles • Local control mechanism maintain constant brain flow • Blood flow to skin () • Blood flow to GIT, KIDNEY (dec) • Generalized S induced art. Vasocon

  11. CV changes during exercise • PR (dec) • Resistance in SK M , heart and skin decreases • MAP (increase) • b/c CO increases to a greater extent than PR decrement

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