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Human Body
Blood-Pressure
Blood-pressure is the propelling force in the arteries. It is a measure of the pressure exerted on the walls of the arteries1 by the flow of blood.
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It depends upon-(a) the output of the heart, and (b) the resistance encountered by the flow in the smaller arteries and arterioles. The pressure in arteries and arterioles reaches a peak called the systolic pressure with each contraction of the heart and then gradually decreases to a minimum, the diastolic pressure, before the next contraction. It is commonly measured in the artery just above the elbow and is always expressed as two figures e.g. 120/80 in healthy young adults. When outside these limits, it is either high or low.
Blood-pressure is an extremely fluctuating physiological function and it is rather difficult to define 'normal' blood-pressure. Firstly, it rises and falls at different times of the day. Secondly, it is higher when one is actively exercising than when one is resting or sleeping. Again, when one is emotionally upset, it rises, and falls down when one becomes calm and quiet. And so the pressure is arbitrarily defined as 'normal' where more than 90 percent of the blood-pressure of population happens to be.
If the pressure is too low, the tissues may not receive adequate supply of nutrients. A few years ago, low pressure was considered undesirable. Nowadays, however, if there are no adverse symptoms, such as dizziness, fatigue or fainting, the low pressure is regarded a protection from the development of atherosclerosis or hardening of the arteris.
Constant high blood-pressure, on the other hand, is definitely injurious. Hardening of the arteries (atherosclerosis is caused by the deposition of the blood clots, fats and calcium on the inside walls of the arteries, making the normally soft elastic arteries to become hard, inelastic and partly or completely blocked.
The risk of developing atherosclerosis is directly related to the level of blood-pressure. If the arteries to the heart, 1. The blood-pressure in the veins is steady and close to zero.
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