CHAPTER XL 



THE VASCULAR SYSTEM CONTINUED: THE GENERAL CIRCULA- 

 TION; THE PULSE AND ARTERIAL PRESSURE; VARIATIONS 

 IN THE CAPILLARY CIRCULATION. 



The general circulation of the blood. — At each beat of the heart 

 the contraction of the ventricles drives a certain quantity of 

 blood, probably amounting to four ounces, with great force into 

 the aorta and pulmonary artery. The aorta delivers this sup- 

 ply of blood from the left ventricle, through its branches, to the 

 capillaries in all parts of the body. In the capillaries, the 

 blood is robbed of oxygen and other constituents necessary for 

 the life and growth of the tissues, is loaded with carbon diox- 

 ide and other waste matters, and is returned by the superior 

 and inferior vense cavoe to the right side of the heart. From 

 the right side of the heart, the blood is conveyed by the pul- 

 monary artery to the capillaries in the lungs,i where it receives 

 a fresh supply of oxygen and gives up the carbon dioxide with 

 which it has become loaded during its circulation through the 

 body. Thus a double circulation is constantly and simultane- 

 ously going on, the artery from the left side of the heart send- 

 ing the pure oxygenated blood to the general system, and the 

 artery from the right side of the heart sending the impure blood 

 to the lungs for purification. The more extensive circulation 

 is usually called the general or systemic circulation, while the 

 lesser circulation is generally known as the pulmonary. 



Some features of the arterial circulation. — The flow of blood 

 into the arteries is most distinctly remittent ; sudden, rapid 



1 It is to be observed that the lungs receive blood from two sources. From 

 the bronchial arteries (branches of the aorta) they receive arterial blood, by 

 means of which the tissues of the lungs are nourished ; and from the pulmonary 

 artery they receive venous blood, which, in passing through the lungs, is arte- 

 rialized by exposure to the air. 



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