The material chosen for inclusion in this review has been arbitrarily selected in the fields of interest to the reviewer. Because of the limit of time included, there has been no attempt to indicate priority of the articles cited or to include all of the publications concerning any single subject.
HEPATIC STRUCTURE AND FUNCTIONThe functional unit of the liver is described as an acinar structure which may be simple or compound or may occur as aggregates of acini (1). Because of the fissures of the liver in animals, the vascular divisions of the portal and hepatic systems branch off in the form of two parallel fans. In the compact liver of man, both systems overlap so that each suprahepatic vein collects blood from two neighboring portal regions and the liver possesses five regions and six segments furnished with afferent and efferent pcdicles (2, 3). Micro angiography of rabbit livers (4) shows that the branches of the portal vein come into the lobules and give rise to sinusoid bundles or divide into two or three venules before they resolve into capillaries. The great venous plexus surrounding the biliary ducts is derived from the portal vein and constitutes a portal system placed at the wall of the intrahepatic biliary pathways before the sinusoidal system. The hepatic artery gives branches to the walls of the biliary ducts, forming a capillary network, and also gives branches to the lobules, these branches opening into the peripheral and central sinusoids. The hepatic veins alternate with portal veins. No direct communications were observed between the branches of the portal vein and hepatic vein ex cept through the numerous sinusoids. After administration of epinephrine, the central vein is empty and marked dilatation occurs in the central sinus oids. The venous plexus of the biliary ducts is constricted. Acetylcholine produces vasodilation of the hepatic vascular system. In other animals, and in the normal human being, there are no nonsinusoidal anastomoses between the portal vein and the hepatic vein or between the hepatic artery and the portal vein (5). With cirrhosis or cancer of the liver there are many shunts from the portal to the hepatic vein and from the hepatic artery to the portal vein. A summary of present concepts ot the control of sinusoidal sphincters and blood flow through the liver suggests that portal-caval anastomoses do occur in normal animals and men (6).Good illustrations of rat liver as viewed with the electron microscope (7) show that the endothelial lining of hepatic sinusoids is predominantly continuous. The small gaps frequently seen are often near a semiattached 1 The survey of literature pertaining to this review was concluded in June 1960. 2 The Mayo Foundation, Rochester, Minnesota, is a part of the Graduate School of the University of Minnesota.