lecture17

lecture17 - Water along with its dissolved molecules...

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lecture 17 arterial end venous end Bulk Flow ! = 28mm Hg P = 35mm Hg Water along with its dissolved molecules (excluding proteins) also moves in and out of the capillaries due to small changes in pressure between the arterial and venous ends of the capillary beds. This is called Bulk Flow . •Water, just like everything else, will move down its concentration gradient. Since Bulk Flow leaves most of the proteins behind in the capillary, water in the interstitial space is more concentrated. This will create a force (pressure) to drive water back into the capillary. Plasma Colloid Osmotic Pressure ( ! ) ! 28 mmHg, and is fairly constant along the length of the capillary. •The blood pressure entering the capillaries has dropped to about 35mm Hg, as a result of passing through the aterioles. Resistance in the capillaries drops the pressure even more to about 15mm Hg at the venous end. The pressure of the interstitial fluid is very low, ! 1mm Hg. Because the capillaries are so permeable the pressure difference drives fluid out of the capillary into the interstitial fluid ( ultrafiltration ) •at the venous end, the plasma colloid osmotic pressure is greater than the capillary blood pressure, so fluid moves back into the capillary ( reabsorption ). ! = 28mm Hg P = 15mm Hg lymphatic system ! if =3 ! if =3 total pressure at arterial end = 35 - (28-3) = 10 mm Hg (positive pressure to leave capillary) total pressure at venous end = 15 - (28-3) = -10 mmHg (negative pressure, so fluid flows in)
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fgure 4-2
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Bulk Flow is important for buffering blood pressure against changes in blood volume: •if blood volume drops, ultrafiltration is reduced and net reabsorption of fluid into the capillary helps compensate by increasing blood volume.
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lecture17 - Water along with its dissolved molecules...

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