Thursday, August 21, 2008

Liver Anatomy

THE LIVER ANATOMY

Pictures from Lippincott Williams & Wilkins Atlas of Anatomy, 1st Edition. 2008


Fig. 1. The Liver (Click image to enlarge)

The liver takes up the majority of the right upper abdominal cavity and extends from the right lateral aspect of the abdomen 15 to 20 cm transversely toward the xiphoid. The weight of the adult liver varies from 1200 to 1800 g, dependent on the overall body size, and constitutes about 1.8% to 3.1% of the total body weight; however, at birth, the liver is larger compared to adjacent thoracic and abdominal viscera and constitutes about 5% to 6% of the body weight.The liver anatomically has four lobes: right, left, caudate, and quadrate. The right lobe accounts for one half to two thirds the total liver volume; however, functionally, the right and left lobes are of about equal size and are divided by a line extending from the inferior vena cava superiorly to the middle of the gallbladder fossa inferiorly. A total of eight functional segments are present, each demarcated by the vascular and biliary drainage: the lateral (segments VI and VII) and medial (segments V and VIII) divisions of the right lobe, the medial (segment IV) and lateral (segments II and III) divisions of the left lobe, and the caudate lobe (segment I), the latter a “watershed” area of the right and left lobe vasculature.

The hepatoduodenal ligament connects the liver to the superior aspect of the duodenum and supports the hilar vessels and duct structures. The transverse fissure separates anteriorly the right lobe from the caudate lobe, whereas the umbilical fissure is located to the left of the quadrate lobe, which itself is bordered on the right by the gallbladder. The peritoneal layers forming the falciform ligament, which extends between the liver and the anterior abdominal wall, separate to form the superior layer of the coronary ligament and the left triangular ligament. The ligamentum teres is located along the lower edge of the falciform ligament and contains the obliterated umbilical vein remnant. The total surface area of the liver is structured by direct continuity with the surrounding abdominal organs, ligaments, and fascia.


Fig.2. Liver Lobes and Ligaments

The portal vein is the main route of vascular drainage of the gastrointestinal tract and is formed through the merger of the superior mesenteric and splenic veins. It also receives blood from the coronary and cystic veins. The portal vein is located along the hepatoduodenal ligament posterior to the hepatic artery and common bile duct and ends at the porta hepatis at the main lobar fissure, dividing into the right and left main branches. The right branch divides early into anterior and posterior segments, whereas the left branch divides into two segments: the pars transversus which extends to the left in the porta hepatis, and the pars umbilicus which descends into the umbilical fossa in line with the left segmental fissure. The caudate lobe veins arise from both the right and left main portal vein branches.

The hepatic vein is composed of three major tributaries (right, middle, left), each having intrahepatic branches. The middle and left hepatic eins often converge to form a single outflow vessel before draining into the inferior vena cava, whereas the right hepatic vein opens through a separate ostium. The caudate lobe drains directly into the inferior vena cava.

Fig.3. Internal Features of Liver (Vascular)


The hepatic artery is a branch of the celiac artery and ascends along the hepatoduodenal ligament and eventually divides into the right and left main branches. The right hepatic artery is usually seen behind the common hepatic duct after giving rise to the cystic artery, and it eventually divides into the anterior and posterior segmental branches. The left hepatic artery obliquely passes upward and to the left in the porta hepatis, eventually dividing into the medial and lateral segmental branches. The quadrate lobe is fed by a middle hepatic artery branch, whereas the caudate lobe is fed by both right and left hepatic artery branches.

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