The Arterial System |
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Our bodies contain a great network of arteries and veins which radiate through all tissues, supplying food and removing the end-products of combustion. In the study of blood-pressure it is the arterial part of the blood system that is the most important, and the path of cure is easier to understand if the reader has some idea of its working. The main arteries begin at the heart, where they are very large. They then decrease in size, until at the distal parts of the body, such as the head and feet, they are approximately only one cell thick. The arteries are in continual movement and have a much stronger construction than the veins; an extra muscular coat allows them to contract and expand in relation to the beau of the heart. When the heart beats strongly the blood is pumped in a surge through the artery, which enlarges slightly as a result of the pressure. The heart then relaxes and the artery contracts because of its elastic nature. This means that the flow of blood is kept more or less continuous by this interaction between the heart and the arterial wall. The arteries never close completely because of the amount of blood contained in the system, and a certain pressure of blood is always present. It follows, therefore, that everyone has a blood-pressure, although it must be understood that, in practice, this pressure is only recorded in the larger arteries. When the more distant parts of the body from the heart are reached by the arterial flow, the blood is oozing rather than flowing into the tissues. |
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