Regulation of Hepatic blood flow

 

Blood supply of liver  25% of cardiac output, 1.5 L/ min Blood supply by hepatic artery (1/3 supply, 98% O2 saturation) and hepatic portal vein (2/3 supply, 70 - 85% O2 saturation) The hepatic triad is formed by the branches of the hepatic artery, hepatic portal vein and bile canaliculus which run together  Portal venue and hepatic arteriole join together to form hepatic sinusoid (specialised capillary system) which optimises exchange with hepatocyte  Venous drainage to IVC via right and left hepatic vein  Regulation of hepatic blood flow  Hepatic artery - extrinsic and intrinsic regulation mechanism  Portal vein - extrinsic regulation  mechanism  Intrinsic mechanism:  Myogenic autoregulation 👉🏻 if drop-in hepatic arterial pressure ➡️ flow is maintained by a decrease in hepatic arterial resistance  Hepatic arterial buffer response 👉🏻 if reduction of flow in portal vein ➡️ compensatory decrease in resistance of hepatic artery to increase arterial blood flow  Extrinsic mechanism: Sympathetic nervous system  The hepatic artery is intervened by alpha and beta receptors, the hepatic portal vein by alpha receptor  The stress response causes vasoconstriction and venosconstriction resulting in reduced hepatic blood flow  The stress response causes an autotransfusion of blood from the hepatic venous reservoir  Other factors affecting:  Right heart function 👉🏻 ⬆️ CVP causes hepatic congestion, ⬇️ CVP causes autotransfusion with venoconstriction  Positive pressure ventilation 👉🏻 ⬇️ hepatic blood flow during inspiration  Hypocapnia 👉🏻 ⬇️ hepatic blood flow due to increased resistance in the portal vein  Anaesthetic agents 👉🏻 hemodynamic effect  Surgical factors: Packing and retraction