. Elementary physiology. Physiology; Physiology. 100 Elementary Fig. 6o.' the entire course of the circulation forms two nearly complete circuits, as shown in the accompanying diagram (Fig. 6i), and a given quantity of blood in a complete round comes twice to the heart. The upper chamber on each side is thin walled, and incapable of exerting or with- standing any great amount of pressure. It is called the auricle^ and its purpose is, by a preliminary contraction,^ to completely fill the lower cham- ber or ventricle before this contracts and drives the blood '.°hyToYd"i^"
. Elementary physiology. Physiology; Physiology. 100 Elementary Fig. 6o.' the entire course of the circulation forms two nearly complete circuits, as shown in the accompanying diagram (Fig. 6i), and a given quantity of blood in a complete round comes twice to the heart. The upper chamber on each side is thin walled, and incapable of exerting or with- standing any great amount of pressure. It is called the auricle^ and its purpose is, by a preliminary contraction,^ to completely fill the lower cham- ber or ventricle before this contracts and drives the blood '.°hyToYd"i^"e?;";rT"°' '"^ ^^e large artery leading away from it. The ventricle on each side is a chamber with very thick muscular walls capable of exerting considerable pressure, when it contracts, upon the blood contained within it. There is a valve arranged between each ventricle and its corresponding auricle which opens towards the ventricle, and another between each ventricle and the large artery which issues from it, open- ing towards the artery (see Figs. 65, (^6). On account of these valves the blood can only move in one direction when the ventri- cular wall contracts upon it, namely, from the ventricle into the artery. There is no valve placed between each auricle and the great veins which enter it, in order to prevent the blood from flowing, when the auricle contracts, from the auricle into these great veins, instead of into the ventricle, because there is less resistance in the direction of the ventricle than in the direction of the veins, and the auricle never gets up sufficient pressure under normal conditions to force the blood back into the veins instead of into the ventricle. When the auricle contracts, the blood is not under pressure in the ventricle, and the effect of ^ The contraction of either auricle or ventricle is known as its systole, and its relaxed or uncontracted condition as its Please note that these images are extracted
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