32 - Chapter 32. BLOOD AS A TISSUE OF INTEGRATION This...

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BLOOD AS A TISSUE OF INTEGRAT ION This chapter reviews some of the material presented in various places in earlier chapters, then introduces a number of new aspects important to the operation of the major vital systems. Blood volume is approximately 6% to 10% by weight (assume 1 liter = 1 kg) of the adult animal. The adult pig is exceptional in having 3.5% to 4.5% of body weight as blood volume. The normal range of pH lies between 7.2 and 7.7, with a typical mean of about 7.4. Arterial blood may be slightly more basic and venous blood slightly more acid. This will be explained later in this section, when buffers are introduced. A. Plasma The non-cellular component of non- coagulated blood is plasma, which accounts for 55% to 70% of blood volume. The plasma volume is determined by measuring the proportion made up by packed cells, the packed cell volume , or hematocrit . The various constituents of plasma include gases, proteins, energy substrates, nonprotein nitrogenous molecules, inorganic salts, vitamins, lipids, and so forth. Some important functions of plasma are obvious: it is the extracellular fluid providing for the suspension and transport of blood cells. It provides for the transport of countless molecules in free solution and also for small hydrophobic molecules in association with the proteins. Lipids are generally hydrophobic and insoluble, but are transported efficiently when they are reversibly bound to plasma proteins. A major function of the plasma proteins is to provide colloid osmotic pressure (that arising from macromolecules) in the blood and thereby to offset ongoing water movement out of the capillary beds and into the tissues. The driving force for this efflux of fluid is simply the hydrostatic pressure present in the vascular bed, a result of the combined effects of the pumping action of the heart and peripheral resistance in the slightly leaky circulatory system. Factors influencing the movement of fluids into and out of the blood vessels are described in the next section. When plasma protein concentrations are subnormal because of malnutrition or chronic blood loss, osmotic recovery of filtered fluid is subnormal and tissue edema will result from net movement of fluid out of the blood and into the interstitium. The plasma proteins also contribute a little to the viscosity of blood, an important hemodynamic factor, as noted earlier in Chapter 18, Section D. B. The formed elements In cattle of about 500 kg live weight, blood volume is 40 L. There are approximately 7 million erythrocytes per mm 3 (i.e. per μ L) of blood. Thus the red blood cell population is of the order of 3 x 10 14 ; the total surface area of these erythrocytes is about 31,000 m 2 , or some 60 m 2 per kg body weight. Some comparative
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This note was uploaded on 03/23/2009 for the course ANSCI 1110 taught by Professor Brucecurrie during the Fall '08 term at Cornell University (Engineering School).

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32 - Chapter 32. BLOOD AS A TISSUE OF INTEGRATION This...

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