210 



ANATOINIY FOR NURSES 



[Chap. XI 



channel by which blood can be conveyed from the lower part of the 

 body to the heart in case of obstruction in the inferior vena cava. 



The portal system. — The gastric, splenic, inferior and superior 

 mesenteric veins which bring back the blood from the intestinal 

 tract do not take it directly to the inferior vena cava. Just back 

 of the pancreas, the splenic and superior mesenteric unite to form 

 the portal vein, and the gastric and inferior mesenteric empty into 

 it. The portal vein runs upward and to the right for about three 

 inches, then enters the liver, where it divides into many small veins, 

 and these finally form plexuses of capillaries. These capillaries 

 unite with another set of capillaries which arise from the hepatic 

 artery, and form the hepatic vein, which carries the blood from the 

 liver to the inferior vena cava. Thus it will be seen that the 

 liver receives blood from two sources — (1) the portal vein which 

 carries blood to the liver in order that certain chemical changes 

 may take place, and (2) the hepatic artery which carries blood to 

 the liver for nutritive purposes. The blood from both sources of 

 supply is carried from the liver by the hepatic vein. 



The portal vein and all its branches constitute the portal system, 

 which is often described as a third or accessorv svstem. 



Arteries " 



SUMMARY 



' Begin as large trunks, grow smaller. 

 Usually deep seated for protection. 



(Two branches of nearlj' equal size. 

 Trunk gives off several branches. 

 One branch that serves as an axis. 

 Anastomosis or inosculation — distal ends unite. 

 Plexus — manj'^ inosculations within limited area. 

 Usually straight (facial and uterine are tortuous). 

 Provides for pulmonary circulation. 



Plight pulmonary artery 

 1. Pulmonary arterj' 



Divisions 



of the 



Vascular 



System 



Pulmonary 

 System 



General 

 System 



— right lung. 

 Left pulmonary artery — 

 left lung. 



2. Capillaries. 



3. Four pulmonary veins — two from each lung. 

 C Pro\'ides for systemic circulation. 



1. Aorta and all its branches. 



2. Capillaries. 



3. Veins empty into heart either directly or by 



means of inferior and superior vena cava. 



