The liver is situated under the right diaphragm in the lower part of the right rib cage. The left lobe of the liver is in the epigastrium and is therefore not protected by the rib cage. The normal liver is firm and has a smooth surface.
The liver parenchyma is divided into functional units called lobules (Figures 42-1 and 42-2). Each lobule is 1–2 mm in diameter and is made up of a maze-like arrangement of interconnected plates of hepatocytes separated by endothelium-lined sinusoids (Figure 42-2). The liver cell plates are arranged radially around the central vein; the liver cells that surround a portal tract comprise the limiting plate. Liver cell plates are normally one hepatocyte in thickness. Individual hepatocytes are large, with a central round nucleus, a prominent nucleolus, and abundant granular cytoplasm.
Liver lobular architecture, showing blood and bile flow. The sinusoids receive blood from branches of the portal vein and hepatic artery and drain into the central vein (solid arrows). Bile drainage is in the opposite direction, toward the portal tracts (dotted arrows).
Detailed structure of the liver lobule, showing blood and bile flow.
The liver cells are separated from the sinusoids by a narrow space (space of Disse) that contains connective tissue and represents the scant interstitial compartment of the liver. Specialized cells of the macrophage system (Kupffer cells) are present in the sinusoids scattered among the endothelial cells.
The biliary system begins at the biliary canaliculi, which are small channels lined by the complex microvilli of surrounding liver cells. The biliary canaliculi form the intralobular bile ductules (canals of Hering), which drain into the bile ducts in the portal tract.
The normal liver has a huge reserve functional capacity. When the liver is normal, about 80% of it can be removed without compromising function. The liver has synthetic, excretory, and metabolic functions.
The liver is the source of plasma albumin; many plasma globulins, including α1-antitrypsin (α-antiprotease); and many proteins of the coagulation cascade.
Many substances are excreted by the liver in bile. The main component of bile is bilirubin. Cholesterol, urobilinogen, and bile acids are also present in bile.
The liver plays a central role in the metabolism of fat, carbohydrates, and protein and in detoxification.
Free fatty acids from adipose tissue and medium- or short-chain fatty acids absorbed in the intestine are brought to the liver. Triglycerides, cholesterol, and phospholipids are synthesized in the liver from the fatty acids and complexed with specific ...