lecture_notes_23_(ta)

lecture_notes_23_(ta) - Lecture 23 Cardiovascular System...

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Lecture 23: Cardiovascular System - Circulation and Blood Pressure III Reading: chapter 10, section: capillaries, pgs 358-373 (pgs 364-379, if using 5 th edition) Additional required reading not covered in lecture: Blood chapter 11, sections: intro, plasma, erythrocytes, pgs 385-390 (pgs 391-396, if using 5 th edition) chapter 11, section: leukocytes, platelets, pgs 392-397 (pgs 398-404, if using 5 th edition) Capillary Exchange - exchange of materials between the blood and the interstitial space ( i.e. extracellular spaces of tissues ) occurs by two passive mechanisms. Because the permeability of capillary walls is so high, the interstitial fluid takes on the same composition as the incoming arterial blood. ( R EMEMBER THAT I NTERSTITIAL F LUID IS ALL FLUID OUTSIDE CELLS THAT IS NOT BLOOD PLASMA . ECF IS ALL FLUID OUTSIDE CELLS ) (1) Diffusion - substances in the blood move independently of one another down their concentration gradients (Figure 10-21) . This is the principal mechanism by which solutes are exchanged between the blood and the tissues. ( EACH SUBSTANCE HAS ITS OWN PARTIAL PRESSURE GRADIENT ) (2) Bulk Flow - This is the principal mechanism by which the distribution of fluid is maintained between the blood and the extracellular space of the tissues. The pores in capillary walls permit the free flow of blood plasma into the interstitial space. The size of the pores is such that blood cells and plasma proteins cannot move into the tissues. Thus the capillary walls can act as a filter to retain some plasma constituents. Bulk flow can occur in both directions, into the tissues from the capillaries (ultrafiltration ( OUT ) ) or into the capillaries from the tissues (reabsorption ( BACK IN ) ) . There are four forces that control the direction of ( BULK ) flow (Figure 10-22) . (1) capillary blood pressure (P c ) - this is the hydrostatic pressure exerted on the inside of the walls of the capillaries. It acts to force fluid out of the capillaries and into the interstitial fluid. The average capillary pressure at the
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lecture_notes_23_(ta) - Lecture 23 Cardiovascular System...

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