Renegade
Forum Elite
Topics: 18
Posts: 171
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a-t b-t c-f d-t (vis a tergo?) e-f
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«The desire to take medicine is perhaps the greatest feature which distinguishes man from animals.» W. Osler
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| vallmo
Forum Junior
Topics: 25
Posts: 37
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Almost: everything is true except e: (explanation given
Standing erect exposes a bloodcolumn to gravity, which raises the pressure in the dependent veins and diminishes venous return (compared with that in the supine position). Because the venous systeme is very compliant, the increase in pressure causes an increas in venous volume, which reduces venous return. Venokonstriktion, which is caused by sympathetic outflow during exercise, partially compensates for the peripheral pooling caused by the effects of gravity.
An increased depth of inspiration casues a more negative pressure in thorax, which increased the pressure gradient along the venous system and improves venous return. Contraction of the skeletal muscles compresses the veins and displaces the blood towards the heart: this effect is enhanced if the venous valves are competent and prevent a backflow of blood between contractions. A reduced arteriol resistance in the skeletal muscles raises capillary and venous presures and increases the flowrate through the systemic cirkúlation.
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