IMG_NEW_0006_001

IMG_NEW_0006_001 - At any one time only about s-t of...

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Blood flow velocity and pressure (Fig' 42'LLl Number of capillaries is ENORMOUS! The TOTAL cross-sectional area of capillaries >>> arteries and veins Velocity of blood flow is SLOWEST in capillaries Blood pressure decreases from arteries to veins 6. Heart and blood vessel function requires regulation Blood flow needs to be regulated to match tissues' metabolic needs, e.g. inactivity vs' activitY Cardiac output = totalvolume of blood ejected from ventricle/minute Cardiac output = heart rate x stroke volume (beats/min) (amount of blood ejected/contraction) Contraction (vasoconstriction) a nd relaxation (vasodilation) of smooth muscle in artery walls modifies blood flow . Cardiac muscle and smooth muscle function controlled bY: . Signals from nervous system (sympathetic and parasympathetic NS) . Hormones in blood (e'g' atrial naturitic PePtide, ANP) . Local control bY endothelium (NO' endothelin)
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Unformatted text preview: At any one time only about s-t}% of capillaries have blood flowing through them Regulated bY: . Amount of blood coming from arteries and arterioles . Contraction of smooth muscle in precaPillary sPhincters Exchange of substances between blood and interstitial fluid across the thin endothelium of capillary walls . Simple solutes (e'g. 02, CO2, sugars, salts) diffuse across cells or through spaces between cells . Movement is aided bY "bulk flow" of fluid driven bY blood Pressure in capillary being >>>> then osmotic pressure (O.P.) . At far end of capillary, accumulation of large proteins increases O.P. and fluid moves back into caPillary . About 85% of fluid is recovered in this way 7. The lymphatic system works with the circulatorY system Lymphatic System returns fluid and proteins to blood (and also has functions in immunity) Fig' 43.7 l...
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