CHAPTER IV 

 CIRCULATION OF BLOOD 



1. INTRODUCTION 



1. IF the blood is to fulfill its function of carrying 

 materials between the organs of the body, it must circulate 

 in the vascular system. 



2. The blood flows from the left ventricle through the 

 aorta and systemic arteries to the capillaries, and from these 

 through the veins and right auricle to the right ventricle; 

 thence through the pulmonary artery, capillaries, and veins 

 and through the left auricle back to the left ventricle 

 (Harvey, 1628). 



The portal vein, formed from the capillaries of the intestine, 

 branches again into capillaries in the liver, which in turn give rise 

 to the hepatic veins. 



3. The difference in blood pressure in the different parts 

 of the vascular system is the cause of the circulation of the 

 blood. The blood is driven from places of higher to those 

 of lower pressure. 



4. The differences in pressure are caused by the rhythmic- 

 ally contracting ventricles which, during their contraction 

 (systole) empty their contents into the aorta and pulmonary 

 artery and, during their relaxation (diastole), take the blood 

 from the auricles and veins. 



5. The valves of the heart prevent the regurgitation of the 

 blood from the ventricles into the veins and from the arteries 

 into the ventricles and thereby determine the flow of blood 

 in one direction. 



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