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 


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