. Adventures with animals and plants. Biology. Fig. 219 In A a vem is bulged at the poiiit where a valve has stopped the backward flow of blood. In B a vem is ctit open through the valve. In which direction does blood flow in this vein? PROBLEM 3. How Materials Are Moved to and fro?H Cells reason a person whose blood pressure is abnormally high should not engage in strenuous exercise. The pressure may rise so much that some smaller vessel may burst, allowing the blood to escape into surrounding tissues. If this happens in the brain there is a cerebral hemorrhage. As the blood escapes and clots
. Adventures with animals and plants. Biology. Fig. 219 In A a vem is bulged at the poiiit where a valve has stopped the backward flow of blood. In B a vem is ctit open through the valve. In which direction does blood flow in this vein? PROBLEM 3. How Materials Are Moved to and fro?H Cells reason a person whose blood pressure is abnormally high should not engage in strenuous exercise. The pressure may rise so much that some smaller vessel may burst, allowing the blood to escape into surrounding tissues. If this happens in the brain there is a cerebral hemorrhage. As the blood escapes and clots, it causes temporary or permanent paralysis by damaging the delicate brain cells. Fainting. It sometimes happens, for a variety of reasons, that the heartbeat is not forceful enough to push the blood uphill into the arteries running into the head. You may have seen a person's face and lips grow pale suddenly. Blood in sufficient amounts is not being sent up into the head; the person loses conscious- ness and loses control of his skeletal muscles; he faints. Frequently he can avoid fainting by holding his head down between his knees or lying flat on his back. Fainting in most cases is not a sign of any special defect. But it should be called to the attention of a physician if it occurs repeatedly. An aviator may have a similar experi- ence. When he makes a very fast and sharp turn or pulls out of a fast dive sharply, the blood in his body is pushed toward the outside of the curve. Since this is away from the head, the blood pressure may not be great enough to force blood to the arteries of the head. As soon as the brain cells fail to receive the necessary oxygen unconsciousness occurs. This is the "blackout" pilots talk about. They "see black" as they faint. As soon as the pressure of blood coming from the heart is greater than the force pushing the blood back the aviator re- covers. 217. Please note that these images are extracted from scanned page images t
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Keywords: ., bookcentury1900, bookpublisherbostondcheath, booksubjectbiology
