Increase in Arterial Pressure During Muscle Exercise and Other Types of Stress
An important example of the ability of the nervous system to increase the arterial pressure is the increase in pressure that occurs during muscle exercise. During heavy exercise, the muscles require greatly increased blood flow. Part of this increase results from local vasodilation of the muscle vasculature caused by increased metabolism of the muscle cells. Additional increase results from simul-taneous elevation of arterial pressure caused by sym-pathetic stimulation of the overall circulation during exercise. In most heavy exercise, the arterial pressure rises about 30 to 40 per cent, which increases blood flow almost an additional twofold.
The increase in arterial pressure during exercise results mainly from the following effect: At the same time that the motor areas of the brain become acti-vated to cause exercise, most of the reticular activat-ing system of the brain stem is also activated, which includes greatly increased stimulation of the vasocon-strictor and cardioacceleratory areas of the vasomotor center. These increase the arterial pressure instanta-neously to keep pace with the increase in muscle activity.
In many other types of stress besides muscle exer-cise, a similar rise in pressure can also occur. For instance, during extreme fright, the arterial pressure sometimes rises to as high as double normal within a few seconds. This is called the alarm reaction, and it provides an excess of arterial pressure that can imme-diately supply blood to any or all muscles of the body that might need to respond instantly to cause flight from danger.
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