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An overview of the liver's anatomy, including its location, size, surface divisions, and the organs it relates to. It also discusses the liver's lobules, the functional unit of the liver, and the hepatic arteries, veins, and ducts.
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Typology: Summaries
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Bob C a r u t h e r s , CST, P h D AST D e p u t y E x e c u t i v e D i r e c t o r
ollowing the concavity of the diaphragm, the liver occupies much of the right upper abdomi- nal quadrant. The largest gland in the body, the liver represents approximately one-fortieth of adult body weight. At its most superior point, the liver lies behind the fifth rib in the right mammary line. The liver's left edge terminates just below the apex of
median line. The liver's inferior border cuts diagonally and at the median line passes approximately midway between the xiphoid process and the umbilicus. The inferior border reaches the right costal margin at the ninth costal cartilage and continues downward and posteriorly. ' The liver's diaphragmatic surface is divided into superior, anterior, right, and posterior sections. The heart produces a shallow fossa-the cardiac impres- sion-where it lies on the liver. The posterior and right parts of the diaphragmatic surface are in contact with the diaphragm and the ribs. The posterior surface contains a sulcus through which the inferior vena cava passes. The falciform ligament subdivides the anterior and superior surfaces, with the anterior surface lying against the diaphragm, costal margin, xiphoid process, and abdominal wall. The liver's visceral surface is separated from the superior section by the inferior border. Posteriorly, the border is rounded and blunt, while anteriorly, it is narrow and sharp. The ligamentum teres notches the inferior border just to the right of the median plane. The^ ' fundus of the gallbladder rests in another shallow fossa farther to the right. The visceral surface, which holds the gallbladder and is indented by the inferior vena cava posteriorly, relates to the other abdominal structures, which project into the right upper quad- rant. They include the right suprarenal gland, right kidney, and the right flexure of the colon, duodenum, and stomach. Hepatic arteries, veins, and ducts enter and exit in the portal region, near the midline of the visceral surface.' The liver can be subdivided into various anatomical and functional parts. Its lobes and
lobule-the basic functional unit of the liver-will be discussed later. 'j In the adult, the liver's peritoneal reflections include the ventral mesogastrium to the anterior abdominal wall and diaphragm, and to the stomach and the duodenum. These reflections produce the falciform ligament, the coronary ligament, and the left and right triangular ligament.' The left gastric artery may have a hepatic branch, which passes to the left lobe of the liver. The common hepatic artery runs along the upper border of the pancreas and passes from behind the peritoneum of the posterior body wall into the lesser omentum at the upper edge of the duodenum. Branches of this artery include the gastroduodenal, proper hepatics, and infrequently, the right gastric. The proper hepatic artery is a continuation of the common hepatic, which follows the gastroduodenal branch. It typically lies to the left of the common bile duct, which is located anterior to the portal vein. Branches of this T h e S u r g i c a l T e c h n o l o g i s t A u g u s t 1 9 9 7 3 1
Right lobe Left lobe Posterior Anterior Medial segment segment segment Lateral segment Figure I-The lobes, segments, and areas of the liver's parietal and visceral surfaces. The liver is the largest gland in the body and is a metabolic powerhouse; however, metabolic activity renders the liver a common site for diseases, many of which require surgical intervention.
right and left hepatic arteries. T h e right anatomical variations of the hepatic hepatic artery usually passes behind the arteries.) Venous drainage is accom- common hepatic duct to the right end of plished through short hepatic veins that the liver hilum, where it branches to open into the inferior vena cava.' enter the right lobe of the liver. T h e left T h e portal vein carries blood to the hepatic artery is longer and smaller than liver from the gastrointestinal tract and the right, and it runs to the left end of typically follows the same distribution as the porta hepatis. Branches reach the the arteries in the liver. T h e portal blood caudate and, occasionally, the quadrate contains products of digestion that serve 3 2 A u g u s t 1 9 9 7 T h e S u r g l a r l T e a h n o l o g l s t as the raw chemical materials on which
blood per minute flow through the liver via a portal vein entrance and a hepatic vein exit. Cirrhosis causes blockage of the portal vein system. In the normal liver, total blood volume is 450 ml, equaling 10% of the total blood volume in the body. High pressure in the heart's right atrium causes backup ptessure in the liver, which can expand as much as 1 L under some conditions. Increased liver pressure can cause fluid transudation from the liver and portal capillaries, leading to a condition known as as-
vessel and duct distribution. Bile ducts follow the distribution of the arteries and portal vein. However, the (^) u hepatic bile ducts do not cross the division between the liver's right and left lobes. Exiting from the liver, the right + and left hepatic ducts join to form the common hepatic duct. T h e common hepatic and cystic ducts then meet to form the common bile duct that empties into the duodenum.' T h e functional unit of the liver-the lobule-was mentioned previously. T h e human liver consists of between 50, and 100,000 individual lobules. Each lobule is cylindrical in structure, several
mm and 2 mm in diameter. Each lobule surrounds a central vein that empties into a hepatic vein. Lobules are composed of hepatic cellular plates radiating from the central vein. Each hepatic plate is one or two cells thick, with small bile canaliculi separating the adjacent cells. These bile canaliculi empty into bile ducts, which lie in the fibrous septa that separate the lobules. T h e fibrous septa also contain portal venules and hepatic arterioles. The
Right lobar Anterior superior area Let%lobar Medial superior area Anterior segmental Posterior inferior area Medial segmental Lateral inferior area Posterior segmental Posterior superior area Lateral segmental Lateral superior area Anterior inferior area Caudate lobar Medial inferior area Caudate process Figure 3-The distribution of hepatic vessels and ducts. Increased liver pressure resulting from pathological conditions can cause fluid transudation from the liver and portal capillaries, leading to the development of ascites. Figure &The structure of the lobule, which is the functional unit of the liver. Between 50,000 and 100.000 individual lobules are contained within the human liver. 3 4 A u g u s t 1 9 9 7 Tha S u r g l c a l Tachnologist