The Blood and its Circulation 



149 



valve into the left ventricle. As soon as the left ventricle 

 is full, it contracts. The mitral valve instantly closes and 

 blocks the passage backward into the auricle ; the blood, 

 having no other way open, is 

 forced past the semilunar valves 

 into the aorta. 



Now red in color from its 

 fresh oxygen, and laden with 

 nutritive materials, the blood is 

 distributed by the arteries to 

 the various tissues of the body. 

 Here it gives up its oxygen and 

 certain nutritive materials to 

 build up the tissues, and receives 

 certain products of waste, and, 

 changed to a purple color, passes 

 from the capillaries into the veins. 



All the veins of the body, 

 except the pulmonary veins and 

 those from the lungs and the 

 heart itself, unite into the two 

 large veins, as already described, 

 which pour their contents into 

 the right auricle of the heart, and 

 thus the grand round of circula- 

 tion is continually maintained. 



This is often called the syste- 

 mic, or greater, circulation. 

 /227. The Portal Circulation. 

 A certain part of the systemic, 

 or greater, circulation is often called the portal circulation. By 

 this is meant the flow of the blood from the abdominal vis- 

 cera through the portal vein and liver to the hepatic vein. 



FIG. 77. Diagram illustrating 

 the Circulation. 



1, right auricle; 2, left auricle; 3, 

 right ventricle ; 4, left ventricle ; 

 5, vena cava superior; 6, vena 

 cava inferior ; 7, pulmonary ar- 

 teries; 8, lungs; 9, pulmonary 

 veins ; 10, aorta ; 11, alimentary 

 canal; 12, liver; 13, hepatic ar- 

 tery; 14, portal vein ; 15, hepatic 

 vein. 



