Chapter 19
- Hepatic Physiology and Pathophysiology
- Phillip S. Mushlin
- Simon Gelman
HEPATIC ANATOMY AND CIRCULATION
Surface anatomy shows the liver to have four distinct topographical
lobes: left, right, caudate, quadrate ( Fig.
19-1
).[1]
The physiologic anatomy, however,
reveals eight functionally independent segments, collectively referred to as the
French (Couinaud) system ( Fig. 19-2
).
Each segment has its own vascular flow and biliary drainage. Couinaud anatomy simplifies
efforts to preserve healthy tissue and extirpate diseased regions, and has resulted
in improved clinical outcomes for patients undergoing hepatic surgery for neoplasms
or trauma-induced injuries.[2]
[3]
[4]
The liver accounts for about 2% of body weight in adults (1.5
kg per 70 kg) and 5% in neonates.[5]
The liver
holds around 10% to 15% of the total blood volume and serves as an important blood
reservoir for the body.[6]
About 20% of blood is
in arteries, 10% is in capillaries, and 70% is in veins.[7]
The hepatic venous circulation directly affects intravascular fluid homeostasis.
[8]
[9]
Even small
increases in hepatic venous pressure can shift large volumes of plasma into the lymphatics
or peritoneal cavity (through Glisson's capsule). The transudated fluid has a protein
concentration similar to that of plasma.
Hepatic Blood Flow
Roughly 25% of the cardiac output passes through the liver (1
mL blood per 1 g liver). The blood supply to the liver is from the hepatic artery
and portal vein ( Fig. 19-3
;
also see Fig. 19-1
).[1]
[10]
After branching from the celiac axis, the
common
hepatic artery divides into the gastroduodenal and proper hepatic arteries. The
latter artery provides 25% to 30% of the total hepatic blood flow and 45% to 50%
percent of the oxygen consumed by the liver. The portal vein—a valveless nutrient
vessel that transports the pooled effluent of pre-portal splanchnic beds—delivers
70% to 75% of the total blood flow to the liver and 50% to 55% of the hepatic oxygen
consumption.[7]
The hepatic artery and portal vein enter the liver at its hilum
(porta hepatis) and course through the liver in parallel, ramifying into consecutively
smaller branches, which end as terminal portal venules and hepatic arterioles. These
terminal branches drain into the hepatic sinusoids
Figure 19-1
Lobar anatomy of the liver. R, right lobe; L, left lobe;
Q, quadrate lobe; C, caudate lobe; v, vein. (From Mushlin PS, Gelman S:
Anesthesia and the liver. In Barash PG, Cullen
BF, Stoelting RK [eds]: Clinical Anesthesia, 4th ed. Philadelphia, Lippincott Williams
& Wilkins, 2001, pp 1067–1101.)
(i.e., capillaries of the liver), which are the main conduits for perfusing hepatocytes
( Fig. 19-4
).[11]
Lining the sinusoids are Kupffer cells, hepatic stellate cells (formerly called
lipid-storing or Ito cells), and fenestrated endothelial cells. Constituents of
blood pass through these fenestrations into the space of Disse, gaining direct access
to hepatic parenchymal cells. Blood leaves the sinusoids through the central veins
(i.e., terminal hepatic venules) and flows into sublobular, lobular, and major hepatic
veins (right, middle, and left, respectively). These veins, and many smaller vessels,
drain into the inferior vena cava ( Fig.
19-5
).[5]
