THE VASCULAR SYSTEM* 



The vascular system conveys food materials and oxygen 

 to the cells of the body, and carries away from these cells 

 the waste products of metabolism. The food substances 

 dissolved in the blood furnish energy for the cell's activi- 

 ties, and materials for replacing the protoplasm which 

 has disintegrated during metabolism. The blood stream 

 tends also to equalize the temperature throughout the 

 body. Still another function is the conveyance of hor- 

 mones from their sources to parts of the body whose activi- 

 ties the hormones accelerate or retard. 



The vascular system carries two fluids — blood and lymph. 

 The former consists of an almost colorless fluid, plasma, 

 and of red (erythrocytes), and white (leucocytes) blood 

 cells. When clotting occurs the plasma is resolved into the 

 fluid serum, which is incapable of clotting under ordinary 

 conditions, and the solid clot of fihri7i. The capacity of 

 blood to form a clot is of primary importance, since it 

 greatly reduces the chance of death through the loss of 

 blood following injury. The red blood cells contain hemo- 

 globin, which has the power of combining with oxygen in 

 the lungs, and carrying it to the tissues, where it is released. 

 Hemoglobin gives the blood its reddish color when exposed 

 to oxygen. There are several types of white blood cells. 



* The discussion of the vascular system is divided into three parts, 

 separated from one another by descriptions of other systems. Experi- 

 ence has shown the convenience of studying the heart and blood 

 vessels anterior to it early in the dissection, of examining the hepatic 

 portal system immediately before the abdominal organs are observed, 

 and of postponing the analysis of the vessels posterior to the heart 

 until after the study of the abdominal contents. 



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