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CIRCULATORY SYSTEM 



veins in the body. The veins from the organs below the heart 

 drain into the lower or inferior vena cava; the veins from 

 the organs above the heart, with the exception of the lungs, 

 lead into the upper or superior vena cava. Both of these large 

 veins empty into the right auricle. From there, blood passes 

 to the right ventricle. This completes the systemic circula- 

 tion. The systemic circulation enables the blood to supply 

 tissues with needed materials and collect excreted materials from 

 them. 



The pulmonary circulation. The right ventricle contracts and 

 sends the blood into the pulmonary artery which divides into two 

 sets of branches, one set going to each lung. In the lungs, these 

 arteries get smaller and smaller until they lead into the capillaries 

 of the lungs. The carbon dioxide, collected from the cells, is 

 given to the lungs and a new supply of oxygen is absorbed through 

 the capillary walls. The blood then travels through veins of in- 

 creasing size until it reaches the large pulmonary veins, which take 

 the blood to the left auricle. This is called the pulmonary or 

 lung circulation. The pulmonary circulation enables the blood to 

 give up the carbon dioxide and take in a new supply of oxygen. 



The portal circulation. 

 As the blood passes 

 through capillaries in the 

 stomach and small intes- 

 tine it absorbs food that 

 has been digested and 

 standardized into end- 

 products. Were all this 

 collected food to circulate 

 until utilized the amounts 

 of nutrients in the blood 



would vary considerably. The nutrients in the blood are kept 

 constant to a large extent by the activity of the liver. The 



The passageway between the left auricle and 

 left ventricle is guarded by a mitral, two-cupped valve. 

 The passageway between the left ventricle and the 

 aorta is also guarded by a valve. By their action, 

 valves allow the blood to flow in only one direction. 



