Anatomy and physiology The liver is the largest solid organ in the body, weighing about 1500 g. It has two lobes, the larger right and the smaller left. The right lobe has two additional lobes, the caudate and the quadrate lobes. Blood supply to the liver is about 1500 ml/min (25% of cardiac output), about 75% from the portal vein and the rest from the hepatic artery. However, each blood vessel supplies about 50% of the liver's oxygen requirements. Normal portal vein pressure is about 10 mm Hg, and normal hepatic artery pressure is arterial. The liver is supplied by sympathetic nerve fibers (T6–11), which when stimulated result in vasoconstriction of the hepatic artery, thereby decreasing the hepatic blood flow.Hepatic blood flow is decreased by any cause that lowers systemic blood pressure and cardiac output. These causes include general and regional anesthesia (spinal/epidural), volatile inhalation agents, positive pressure ventilation (and positive end-expiratory pressure [PEEP]), hypoxemia, β-blockers, and α1-agonists. The liver performs several important functions in the body, including metabolic functions (carbohydrate, fat, protein, and drug metabolism), bile secretion, bilirubin excretion, albumin production, ammonia excretion, and synthesis of all the clotting factors, except factor VIII.
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