. A text-book of physiology : for medical students and physicians . nd the side pressure increases in a straight line from the point of exit 510 BLOOD-PRESSURE AND BLOOD-VELOCITY. 511 to the reservoir, and this in general is the picture presented bythe circulation. The reservoir, the head of pressure, is representedby the aorta, the exit for the outflow by the opening of the venaecavse into the right auricle, and the side pressure or internal tensionof the blood due to friction against the walls of the vessels increasesfrom the venae cavse back to the aorta. If from aorta to vena cav
. A text-book of physiology : for medical students and physicians . nd the side pressure increases in a straight line from the point of exit 510 BLOOD-PRESSURE AND BLOOD-VELOCITY. 511 to the reservoir, and this in general is the picture presented bythe circulation. The reservoir, the head of pressure, is representedby the aorta, the exit for the outflow by the opening of the venaecavse into the right auricle, and the side pressure or internal tensionof the blood due to friction against the walls of the vessels increasesfrom the venae cavse back to the aorta. If from aorta to vena cavathe vessels were of the same diameter the increase would be in astraight line, as in the case of the model. In this model it will benoticed that the straight line showing the side pressure does notstrike the top of the column of liquid in the reservoir, but corre-sponds to a certain height, hi. This expresses the fact that, of thetotal head of pressure in the reservoir, which we may designate asH, a certain portion only, but a large portion, hf, is used in over-. Fig. 208.—Schema to illustrate the side pressure due to resistance, and the velocity pres-sure (Tigerstedt): H, A reservoir containing water; 1, 2, 3, 4, 5,_ the outflow tube withgauges set at right angles to nieasure the side pressure; h, the portion of the total pressureused in overcoming the resistance to the flow; h, the portion of the total pressure used inmoving the column of liquid—the velocity pressure. coming the resistance along the tube. What is left—that is, H-h,represents the force that is employed in driving the liquid throughthe tube with a certain velocity; this portion of the pressure we mayspeak of as the velocity pressure, h. If in measuring the side pressureat any point the gauge were prolonged into the tube and bent so asto face the stream, this velocity pressure would add itself to theside pressure at that point and the water would rise to a higherlevel in this particular tube. There are tw
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