The largest solid organ in the body, situated on the right side below the diaphragm. The liver occupies the right hypochondrium, the epigastrium, and part of the left hypochondrium, and is level with the bottom of the sternum. Its undersurface is concave and covers the stomach, duodenum, hepatic flexure of colon, right kidney, and adrenal capsule. The liver secretes bile and is the site of numerous metabolic functions.
LIVER AND GALLBLADDER
The liver has four lobes, five ligaments, and five fissures and is covered by a tough fibrous membrane, Glisson's capsule, which is thickest at the transverse fissure. At this point the capsule carries the blood vessels and hepatic duct, which enter the organ at the hilus. Strands of connective tissue originating from the capsule enter the liver parenchyma and form the supporting network of the organ and separate the functional units of the liver, the hepatic lobules.
The many intrahepatic bile ducts converge and anastomose, finally forming the secretory duct of the liver, the hepatic duct, which joins the cystic duct from the gallbladder to form the common bile duct or the ductus choledochus, which enters the duodenum at the papilla of Vater. A ring of smooth muscle at the terminal portion of the choledochus, the sphincter of Oddi, permits the passage of bile into the duodenum by relaxing. The bile leaving the liver enters the gallbladder, where it undergoes concentration principally through loss of water absorbed by the gallbladder mucosa. When bile is needed in the small intestine for digestive purposes, the gallbladder contracts and the sphincter relaxes, thus permitting escape of the viscid gallbladder bile. Ordinarily, the sphincter of Oddi is contracted, shutting off the duodenal entrance and forcing the bile to enter the gallbladder after leaving the liver.
The functional units of the liver are the liver lobules, six-sided aggregations of hepatocytes permeated by capillaries called sinusoids. Lining these sinusoids are Kupffer cells, the macrophages of the liver.
The blood supply consists of oxygenated blood from the hepatic artery, a branch of the celiac artery, and blood from all the digestive organs and spleen by way of the portal vein. The end products of digestion and other materials thus pass through the liver before entering general circulation.
The nerve supply consists of parasympathetic fibers from the vagi and sympathetic fibers from the celiac plexus via the hepatic nerve.
The liver is one of the most metabolically active organs of the body. Amino acid metabolism: It synthesizes nonessential amino acids, deaminates excess amino acids for use in energy production, and forms urea, which the kidneys excrete. Bile production: It is responsible for the production of bile salts, which emulsify fats in the small intestine; 800 to 1000 mL of bile is secreted in 24 hr, and the secretion rate is increased greatly during digestion of meals rich in fats. Carbohydrate metabolism: It converts monosaccharides other than glucose to glucose, and stores excess glucose as the starch glycogen, until such energy is needed. Detoxification: It produces enzymes to metabolize potentially harmful substances found in the portal circulation, e.g., alcohol, ammonia, indole, many medications, and skatole, into less toxic ones. Endocrine functions: It facilitates the conversion of levothyroxine to the more metabolically active thyroid hormone, triiodothyronine. Excretion: It discharges the breakdown products of hemoglobin (bilirubin and biliverdin) into the bile; these are eliminated in feces. Fat metabolism: It synthesizes cholesterol as well as lipoproteins for the transport of fat to other body tissues; it converts fatty acids to acetyl groups or ketones, so they may be used as energy sources. Phagocytosis: Its macrophages (Kupffer cells) scavenge bacteria, other pathogens, and senescent red blood cells from the portal circulation. Protein synthesis: It manufactures albumin, alpha-globulins and beta-globulins, complement components, and clotting factors, some of which are dependent on vitamin K. Storage: It stores copper, iron, vitamin B12, and the fat-soluble vitamins A, D, E, and K.
The liver is examined by inspection, auscultation, percussion, and palpation. Inspection of the organ includes indirect assessments, e.g., for jaundice (skin color), palmar erythema, and spider telangiectasias and other signs of chronic liver disease. Auscultation of the liver may reveal bruits associated with liver cancer; auscultation also is used to make a crude estimate of organ size. Percussion of the liver, which is performed in the right midclavicular line, provides another method for roughly estimating size. Palpation of the organ may reveal tenderness, irregular edges, masses, or tumors.
(A) LIVER AND GALLBLADDER, (B) LOBULE
An enlargement of the liver caused by the deposition of amyloid proteins.
SYN: SEE: lardaceous liver
The liver is enlarged, smooth, firm, and painless. Infiltration of other organs may cause kidney failure, intercerebral bleeding, heart failure, anemia, and other diseases and conditions.
The prognosis is unfavorable.
A biomechanical device typically combining a system of filters to remove toxins from the blood with hepatic cells or tissue. It is designed to support patients with hepatic failure temporarily until a donor liver becomes available for transplantation.
Cirrhosis of the liver caused by fibrous tissue formed, as a result of infection or obstruction of the bile ducts.
Degenerative changes in liver cells owing to fat deposits in hepatocytes.
SYN: SEE: steatohepatitis
An easily displaced liver.
SYN: SEE: wandering liver
The presence of gas bubbles in the liver as a result of infection with anaerobic bacteria. This produces a honeycomb appearance in the liver tissue.
Degeneration of the liver characterized by fatty changes, fibrous scarring, nodular degeneration, and atrophy of the liver with the surface covered with brown or yellow nodules. This condition is seen in chronic alcoholism and malnutrition.
SEE: Amyloid liver.
Chronic passive congestion of the liver, which produces a reddened central portal area and a yellowish periportal zone.
A colloquial term for injury to the liver resulting from insufficient blood flow, e.g., in patients who have suffered an episode of severe hypotension. A hallmark of this condition is a sudden and marked elevation in liver enzyme levels, such as alanine aminotransferase (ALT).
SEE: Floating liver.
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