Blood Flow and Pressure (Fundamentals)

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Blood Flow and Pressure Intro

PROPERTIES OF FLUIDS All fluids exert hydrostatic pressure Blood pressure: hydrostatic force that blood exerts against vessel walls (propels blood through vascular system)

DIRECTION OF BLOOD FLOW Aorta (largest artery) ? smaller arteries ? arterioles ? capillaries ? venules ? veins ? vena cava (largest vein)

Blood Pressure (mm Hg)

Variables:

Stroke volume Heart rate Cardiac output Peripheral resistance: Total cross sectional area & Luminal diameter of vessels (vasoconstriction/vasodilation)

Average diastolic pressure: 75 mm Hg Average systolic pressure: 110 mm Hg

AORTA & ARTERIES > arterioles > capillaries > venules > veins and vena cava

Pressure drops in arterioles until 0 mm Hg in veins Mechanisms of venous return: 1. Skeletal muscle 2. Respiratory inspiration

Total Cross Sectional Area

Aorta < arteries < arterioles < CAPILLARIES > venules > veins > vena cava

Total cross sectional area: directly proportional to peripheral resistance Increase in total cross sectional area ? increase in surface area of vessel walls

Velocity

AORTA & ARTERIES > arterioles > capillaries < venules < VEINS & VENA CAVA

Velocity increases at venules because of venous return mechanisms (velocity in veins & vena cava < aorta & arteries)

Peripheral resistance

Vasoconstriction: smooth muscle contracts ? reduce diameter ? increase peripheral resistance

Vasodilation: smooth muscle relaxes ? increase diameter ? decrease peripheral resistance

All vessels can adjust diameter except capillaries (lack smooth muscle)

Blood Flow and Pressure (Fundamentals)

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