THE GREAT VESSELS 317 



vena cava the direction of the blood-stream is upwards only, 

 towards the superior vena caval system. 



The hepatic veins, which are the last tributaries received 

 by the inferior vena cava, return the blood conveyed to 

 the liver both by the hepatic artery and by the portal vein 

 (p. 261). Regurgitation of blood into the inferior vena cava 

 from the right atrium will therefore produce not only the signs 

 of vena caval obstruction but also the signs of portal obstruc- 

 tion. In this condition the effects are first to be observed in 

 the liver, owing to the retardation of the outflow from the 

 hepatic veins. The organ becomes greatly distended and 

 projects downwards considerably beyond the costal margin. 

 On palpation, pulsations are readily detected and, when they 

 are carefully examined, they are found to occur just before the 

 apex-beat. Tracings of the hepatic pulse correspond precisely 

 to tracings of the jugular pulse, because they are both pro- 

 duced in the same way. 



Unless the right atrium recovers its tone, other signs of vena 

 caval obstruction follow dilatation of the liver. Owing to the 

 retardation of the outflow through the renal veins and the 

 consequent disturbance of the functions of the kidneys, the 

 urine is scanty in quantity and contains albumen. The 

 general venous congestion leads to an increased transudation 

 of serum into the peritoneal sac and, as the stomata (p. 240) 

 are unable to carry it away with sufficient rapidity, the con- 

 dition of ascites develops. 



The Pulmonary Veins convey the oxygenated blood from 

 the lungs to the left atrium. There are usually two on each 

 side, but they may unite to form a common trunk before 

 entering the heart. Dilatation of the left atrium (auricle) 

 retards the outflow from the pulmonary veins, and, as a result 

 of the venous congestion within the lung, an increased 

 transudation of serum occurs into the pleural sacs. As this 

 variety of hydrothorax is not inflammatory in origin, the fluid 

 in most cases is not limited by adhesions, and it therefore 

 gravitates down to the lowest recesses of the pleural sacs. 



