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In these capillaries mediated transport moves water

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In these capillaries, mediated transport moves water-soluble sub-stances across the capillary walls (see chapter 13 for a descriptionof the blood-brain barrier).Superficialtemporal arteryCommoncarotid arteryFacial arteryAxillary arteryBrachial arteryRadial arteryFemoral arteryPopliteal artery(behind knee)Dorsalispedis arteryPosteriortibial arteryFIGURE 21.35Major Points at Which the Pulse Can Be MonitoredEach pulse point is named after the artery on which it occurs.
747CHAPTER 21Cardiovascular SystemNet hydrostatic pressure=BPIFP=10(3)=13 mm HgThe concentration of proteins within capillaries and the con-centration of proteins within interstitial fluid do not change sig-nificantly because only a small amount of fluid passes from thecapillaries into the tissue spaces. Therefore, the net osmotic pres-sure moving fluid into capillaries by osmosis is still approximately20 mm Hg. At the venous end of capillaries, the NFP now causesfluid to reenter the capillary:NFP=Net hydrostatic pressureNet osmotic pressure=1320=7 mm HgExchange of fluid across the capillary wall and movement offluid into lymphatic capillaries keep the volume of the interstitialfluid within a narrow range of values. Disruptions in the movementof fluid across the wall of the capillary can result in edema, orswelling, as a result of increased interstitial fluid volume.The greater the osmotic pressure of a fluid, the greater thetendency for water to move into that fluid (see chapter 3). The netosmotic pressure results in the osmosis of water into the capillarybecause water has a greater tendency to move into the blood thaninto the interstitial fluid.The net filtration pressure at the arterial end of the capillaryis equal to the net hydrostatic pressure, which moves fluid out ofthe capillary, minus the net osmotic pressure, which moves fluidinto the capillary. Since the net hydrostatic pressure is greater thanthe net osmotic pressure at the arterial end of the capillary, thereis a net movement of fluid out of the capillary:NFP=Net hydrostatic pressureNet osmotic pressure=3320=13 mm HgBetween the arterial and venous ends of capillaries, the bloodpressure decreases from about 30 mm Hg to 10 mm Hg. This causesa reduction in the net hydrostatic pressure moving fluid out of thevenous end of the capillary:123The outward movement offluid due to the net hydrostaticpressure (red arrow; 33 mm Hg)is greater than the inwardmovement of fluid due tothe net osmotic pressure(blue arrow;20 mm Hg).1/10 volume to lymphatic capillaries9/10 volume returns to capillaryThe inward movement offluid due to the net osmoticpressure (blue arrow;20 mm Hg) is greater thanthe outward movement offluid due to net hydrostaticpressure (red arrow;13 mm Hg).At the arterial end of the capillary, thenet hydrostatic pressureis greaterthan thenet osmotic pressure.Whenthe net osmotic pressure is subtractedfrom the net hydrostatic pressure, theresult is a positivenet filtrationpressurethat causes fluid to move outof the capillary.33 mm Hg (Net hydrostatic pressure)20 mm Hg (Net osmotic pressure)13 mm Hg (Net filtration pressure)Approximately nine-tenths of the fluid thatleaves the capillary at its arterial endreenters the capillary at its venous end.About one-tenth of the fluid passes intothe lymphatic capillaries.At the venous end of the capillary, thenet hydrostatic pressureis less thanthenet osmotic pressure.When the netosmotic pressure is subtracted from thenet hydrostatic pressure, the result is anegativenet filtration pressurethatcauses fluid to move into the capillary.13 mm Hg (Net hydrostatic pressure)20 mm Hg (Net osmotic pressure)7 mm Hg (Net filtration pressure)

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Term
Summer
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Tags
Internal carotid artery, Common carotid artery, Arteries of the head and neck

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