A dynamic and static study of hepatic arterioles and hepatic sphincters

Abstract

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.The liver consists of many identical morphological units that fulfill its numerous functions. Each unit is microscopic in size and consists of a sinusoid with its afferent and efferent vascular connections and the surrounding hepatic tissue with its biliary, lymphatic and nervous connections. As liver function is dependent upon the conveyance of substances to and from these functional units, a knowledge of the dynamic anatomic and physiologic relationships of the vascular system with each unit is required for an understanding of liver function.The current concept of the hepatic microvascular system is based primarily upon the investigation of the living liver of frogs by Knisely et al. ('48), and in mammals by Irwin and MacDonald ('53) and Bloch ('55). Several structures seen in the living liver by these investigators, however, were seen infrequently, were resolved incompletely, or have not been seen by others. As a result the following problems have been answered only partially: (1) the reason for the closure of most of the hepatic arterioles during anesthesia is unknown; (2) the cytology of the afferent Ann. J. ANAT., 119: 455-478. and efferent sphincters of the sinusoids is almost unknown; and (3) the local and hormonal regulation of blood flow through the sinusoids is understood poorly.The purpose of this investigation was to demonstrate in life the cytology of the afferent and efferent sphincters and to elucidate the local and hormonal factors that acted on these structures to regulate the flow of portal and arterial blood through the sinusoids. 455

Origins of Portal Hypertension in Nonalcoholic Fatty Liver Disease

“…Intralobular arterioles occasionally drain to sinusoids midway between zones 1 and 3 in the classic liver lobule [58]. The impact of these "arterial twigs" on sinusoidal flow is incompletely understood, although they may represent areas of higher pressure [59]. In a recent review of liver biopsies from patients with steatohepatitis, centrilobular arteries were common in cases with higher-stage fibrosis and occurred in 60% of livers with stage 1b (moderate zone 3 perisinusoidal) fibrosis [60].…”

The hepatic circulation in health and disease: Report of a single-topic symposium

“…The hepatic artery supplies distinct anatomic locations before anastomosing with portal vein-derived blood in the sinusoids. [49][50][51][52] These locations include the peribiliary plexus, the portal tract interstitium, portal vein vasa vasorum, Glisson' s capsule, and the vasa vasorum of the central, sublobular, and hepatic veins. 53 The arterioles that travel in the portal tract and supply blood to the wall of the portal vein, bile ducts, and portal tract interstitium form distinct collecting vessels termed the hepatic artery-derived portal system, which subsequently flow through the hepatic lobules, anastomosing with portal vein-derived blood.…”

Endothelin induced contractility of stellate cells from normal and cirrhotic rat liver: implications for regulation of portal pressure and resistance

“…After stabilization, bosentan was perdal or postsinusoidal mechanisms. [25][26][27][28][29] By modulating the di-fused continuously (flow rate of approximately 2.0 mL/gm/min) at concentrations of 2 mg% or 10 mg% for 50 minutes. The maximal change in portal ameter of sinusoids, stellate cells have been proposed to regupressure is shown.…”