274 THE DIGESTIVE SYSTEM 



These, then, are the viscera which will be affected primarily 

 in portal obstruction. 



Portal Obstruction. The portal circulation may be 

 obstructed in the liver itself by hepatic cirrhosis the 

 commonest cause or by tumours, either of liver or stomach, 

 in the neighbourhood of the porta hepatis. More rarely, the 

 portal vein may be obstructed by malignant disease of the 

 head of the pancreas. Whatever the cause, the symptoms 

 referable to obstruction of the portal circulation are always the 

 same. The walls of the stomach become the site of venous 

 congestion, the veins become dilated and some may rupture, 

 causing haematemesis. A similar condition affects the walls 

 of the alimentary canal, for the larger veins of the portal 

 system do not possess any valves. On this account intestinal 

 derangement, which is usually characterised by alternate 

 periods of diarrhoea and constipation, is brought about and 

 internal haemorrhoids are found in the lower part of the 

 rectum. 



Backward pressure along the splenic vein causes venous 

 congestion of the spleen, which usually becomes enlarged 

 and may project from under the left costal margin. The 

 increase in size of the spleen is one of the most constant 

 concomitants of portal cirrhosis. 



Stasis of the mesenteric veins not only affects the intestinal 

 canal, but it also causes an increased transudation of serum 

 into the peritoneal cavity, and, as the peritoneal stomata 

 (p. 240) are not able to remove it with sufficient rapidity, the 

 condition of ascites is brought about. The subsequent action 

 of the stomata is further hampered by a chronic thickening of 

 the peritoneum, which usually accompanies the condition. 



Communications between the Portal and the Systemic 

 Veins. Although obstruction to the portal circulation is only 

 completely compensated in exceptional cases, the condition is 

 always accompanied by a dilatation of the normal channels 

 of communication which connect the systemic to the portal 

 system of veins. 



