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)
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
AORTA & ARTERIES > arterioles > capillaries < venules < VEINS & VENA CAVA
Velocity increases at venules because of venous return mechanisms
(velocity in veins & vena cava < aorta & arteries)
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)
