ANGIOLOGY: THE VASCULAR SYSTEM 



Angiology is the description of the organs of circulation of the blood and 

 lymph — the heart and vessels. The heart is the central hollow muscular organ 

 which functions as a suction and force pump; the differences in pressure caused 

 by its contraction and relaxation determine the circulation of the l)lood and lymph. 

 It is situated in the middle mediastinal space of the thorax, between the two lungs, 

 and is inclosed in a fibro-serous sac — the pericardium. The vessels are tubular 

 and run through almost all parts of the body. They are designated according to 

 their contents as blood- and lymph-vessels. 



The blood- vascular system consists of: (1) the arteries, which convey l)loocl 

 from the heart to the tissues; (2) the capillaries, microscopic tubes in the tissues 

 which permit of the necessary interchange between the blood and the tissues; 

 (3) the veins, which convey the blood back to the heart. 



The blood-vessels are divided into the pulmonary and the systemic. The 

 pulmonary artery conveys the l^lood from the right ventricle of the heart to the 

 lungs, where it is arterialized, and is returned by the pulmonary veins to the left 

 atrium of the heart, and passes into the left ventricle. The systemic arteries 

 convey the blood from the left ventricle all over the body, whence it is returned by 

 the venae cavae to the right atrium, and passes into the right ventricle. 



It should be noted, however, that the lungs receive arterial blood through the systemic 

 bronchial arteries. This blood is returned in part by the bronchial veins to the right atrium 

 (indirectly), in part by the pulmonary veins to the left atrium. 



The term portal system is often applied to the portal vein and its tributaries 

 which come from the stomach, intestine, pancreas, and spleen. The vein enters 

 the liver, where it branches like an artery, so that the blood in this subsidiary 

 system passes through a second set of capillaries before being conveyed to the heart 

 by the hepatic veins antl the posterior vena cava. 



The arteries (Arteriae), as a rule, divide at an acute angle, giving off finer 

 and finer branches. In some cases branches come off at a right angle, and others 

 are recurrent, i. e., run in a direction opposite to that of the parent stem. The 

 intercommunication of l)ranches of adjacent arteries is termed anastomosis. Most 

 commonly the connections are made by a network of numerous fine branches 

 (Plexus vasculosus). Relatively large communicating branches (Rami connnuni- 

 cantes) occur in certain places; they may be transverse or in the form of arches. 

 Wide-meshed networks of vessels are termed Retia vasculosa. Terminal or end ar- 

 teries are such as form isolated networks, i. c, do not anastomose with adjacent ar- 

 teries. A rete mirabile is a network intercalated in the course of an artery. A 

 collateral vessel ( \'as coUaterale) is one which pursues a course near and similar 

 to that of a larger vessel. 



The veins (Venae) are in general arranged like the arteries, but are usually of 

 greater caliber. When a vein accompanies an artery, it is termed a vena comitans 

 or satellite vein ; in many places two veins accompany a single artery. The primi- 

 tive venous trunks do not run with the arteries, and most of the superficial veins 

 (Venae cutaneae) pursue independent courses. They anastomose even more freely 

 than the arteries, and large communicating ])ranches are very common. The veins 

 form ver}^ rich plexuses (Plexus venosi) in many places. Some veins which are 

 without independent walls and are inclosed by dense membranes and run usually 



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