A dynamic and static study of hepatic arterioles and hepatic sphincters

The purpose of this investigation was to demonstrate the cytology of the sphincters of hepatic sinusoids, to elucidate further the pathway by which arterial blood is distributed to the sinusoids, and to study the hormonal and local regulation of arterial and portal venous blood flow through the sinusoids. The sphincters were found to consist of reticulo-endothelial cells and were the primary site for the regulation of blood flow through the sinusoids. By contracting independently or in unison the flow of blood was regulated through individual sinusoids, through sinusoids supplying a portion of a lobule, or through sinusoids supplying a whole lobule. When the sphincter cells contracted, their nuclear region bulged into the lumen, thereby occluding it. Hepatic arterioles were found to wind around adjacent portal venules with an average curvature of 42° and communicated with sinusoids via arterio-sinus twigs. No structural arterio-portal anastomoses were observed; however, functional “arterioportal anastomoses” were formed by short twigs which terminated in sinusoids near their origins. No branches were found to terminate near central venules. The data suggest that the local regulation of blood flow through the hepatic sinusoids is mediated by vasodilator metabolites (adenosine and/or potassium) released from hypoxic hepatic cells as a result of the rapid glycogenolysis that accompanies hepatic cellular hypoxia.