CHAPTER XI 

 THE CIRCULATION OF BLOOD 



THE PULMONARY CIRCULATION 



This is the circulation of the blood through the lungs, that it 

 may become aerated or purified. 



The pulmonary artery leaves the right ventricle, carrying 

 impure blood, and soon divides into two branches, the right and 

 left pulmonary arteries (one for each lung), which break up into a 

 capillary network around the air cells. From this network veins 

 arise which, by uniting, form two from each lung, making the four 

 pulmonary veins carrying purified blood to the left side of the heart. 

 They enter the left atrium. 



THE SYSTEMIC CIRCULATION 



This is the circulation of the blood through the entire body or 

 "system," that it may nourish the tissues and organs (Fig. 126). 



Arteries of the Systemic Circulation 1 



The aorta (Fig. 127), having received pure blood from the lungs, 

 leaves the left ventricle, arches over the root of the left lung to the 

 left side of the fourth thoracic vertebra, then (gradually coming 

 to the front of the spinal column) passes down through the 

 diaphragm, and ends by dividing at the fourth lumbar vertebra 

 (a little below the level of the umbilicus). Thus it consists of 

 three portions: the arch, the thoracic aorta, and the abdominal 

 aorta. 



The arch of the aorta extends from the heart to the body 

 (lower border) of the fourth thoracic vertebra. It reaches 

 almost as high as the sternal (or jugular) notch. 



It may be felt in thin persons by pressing the finger tip down behind the 

 bone. 



1 The names of all of the arteries are given in tabular form on page 379. Only 

 the principal ones are here described. 



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