Physiology and Hygiene for Secondary Schools by Francis M. Walters;A.M.
page 55 of 527 (10%)
page 55 of 527 (10%)
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capacity than the system of arteries.
[Fig. 20] Fig. 20âVein split open to show the valves. *Why the Arteries are Elastic.*âThe elasticity of the arteries serves a twofold purpose. It keeps the arteries from bursting when the blood is forced into them from the ventricles, and it is a means of _supplying pressure to the blood while the ventricles are in a condition of relaxation._ The latter purpose is accomplished as follows: Contraction of the ventricles fills the arteries overfull, causing them to swell out and make room for the excess of blood. Then while the ventricles are resting and filling, the stretched arteries press upon the blood to keep it flowing into the capillaries. In this way _they cause the intermittent flow from, the heart to become a steady stream in the capillaries_. The swelling of the arteries at each contraction of the ventricle is easily felt at certain places in the body, such as the wrist. This expansion, known as the "pulse," is the chief means employed by the physician in determining the force and rapidity of the heartâs action. *Purpose of the Valves in the Veins.*âThe valves in the veins are not used for directing the _general_ flow of the blood, the valves of the heart being sufficient for this purpose. Their presence is necessary because of the pressure to which the veins are subjected in different parts of the |
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