Physiology and Hygiene for Secondary Schools by Francis M. Walters;A.M.
page 54 of 527 (10%)
page 54 of 527 (10%)
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layers, or coats, in their walls. The corresponding coats in the arteries
and veins are made up of similar materials, as follows: 1. _The inner coat_ consists of a delicate lining of flat cells resting upon a thin layer of connective tissue. The inner coat is continuous with the lining of the heart and provides a smooth surface over which the blood glides with little friction. 2. _The middle coat_ consists mainly of non-striated, or involuntary, muscular fibers. This coat is quite thin in the veins, but in the arteries it is rather thick and strong. 3. _The outer coat_ is made up of a variety of connective tissue and is also much thicker and stronger in the arteries than in the veins. [Fig. 19] Fig. 19âArtery dissected to show the coats. Marked differences exist between the arteries and the veins, and these vessels are readily distinguished from each other. The walls of the arteries are much thicker and heavier than those of the veins (Fig. 19). As a result these tubes stand open when empty, whereas the veins collapse. The arteries also are highly elastic, while the veins are but slightly elastic. On the other hand, many of the veins contain valves, formed by folds in the inner coat (Fig. 20), while the arteries have no valves. The blood flows more rapidly through the arteries than through the veins, the difference being due to the fact that the system of veins has a greater |
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