liver (redirected from liver fluke disease)

liver, largest glandular organ of the body, weighing about 3 lb (1.36 kg). It is reddish brown in color and is divided into four lobes of unequal size and shape. The liver lies on the right side of the abdominal cavity beneath the diaphragm. Blood is carried to the liver via two large vessels: the hepatic artery carries oxygen-rich blood from the aorta, and the portal vein carries blood containing digested food from the small intestine. These blood vessels subdivide in the liver repeatedly, terminating in minute capillaries. Each capillary leads to a lobule. Liver tissue is composed of thousands of lobules, and each lobule is made up of hepatic cells, the basic metabolic cells of the liver. One of the liver's major functions is the manufacture and secretion of bile, which is stored in the gall bladder and released in the small intestine. Bile salts emulsify fats, a process that prepares the latter for digestion by the intestinal enzymes (see digestive system). The hepatic cells assimilate carbohydrates, fats, and proteins. They convert glucose to its stored form, glycogen, which is reconverted into glucose as the body requires it for energy. The ability of the liver to maintain the proper level of glucose in the blood is called its glucose buffer function. The end products of fat digestion, fatty acids, are used to synthesize cholesterol and other substances needed by the body. Excess carbohydrates and protein are also converted into fat by the liver. Digested proteins in the form of amino acids are broken down further in the liver by deamination. Part of the amino acid molecule is converted into glycogen and other compounds. Urea, a waste product of protein breakdown, is produced by the liver, a process which removes poisonous ammonia from the body fluids. The liver is also capable of synthesizing certain amino acids (the so-called nonessential amino acids) from other amino acids in a process called transamination. Some essential components of blood are manufactured by the liver, including about 95% of the plasma proteins and the blood-clotting substances (fibrinogen, prothrombin, and other coagulation factors). The liver also filters harmful substances from the blood. Phagocytic cells in the liver, called Kupffer cells, remove large amounts of debris and bacteria. In addition, the liver stores important vitamins and minerals, including vitamins A, D, K, and B₁₂. Several diseases states can affect the liver, such as hepatitis (an inflammation of the liver) and cirrhosis (a chronic inflammation that progresses ultimately to organ failure). Alcohol alters the metabolism of the liver, which can have overall detrimental effects over long periods of abuse. In 1994, a bioartificial liver, part machine, part cloned living liver cells, was used for the first time. Functioning somewhat like a kidney dialysis machine, the bioartificial liver can support patients with acute liver failure until their own livers regenerate, or it can be used by patients while waiting for a liver transplant.

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liver

Largest gland in the body, with several lobes. It secretes bile; metabolizes proteins, carbohydrates, and fats; stores glycogen, vitamins, and other substances; synthesizes coagulation factors; removes wastes and toxic matter from the blood; regulates blood volume; and destroys old red blood cells. The portal vein carries blood from the gastrointestinal tract, gallbladder, pancreas, and spleen to the liver to be processed. A duct system carries bile from the liver to the duodenum and the gallbladder. Liver tissue consists of a mass of cells tunneled with bile ducts and blood vessels. About 60% are hepatic cells, which have more metabolic functions than any other cells. A second type, Kupffer cells, play a role in blood-cell formation, antibody production, and ingestion of foreign particles and cell debris. The liver manufactures plasma proteins, including albumin and clotting factors, and synthesizes enzymes that modify substances such as nutrients and toxins, filtered from the blood. Liver disorders include jaundice, hepatitis, cirrhosis, tumours, vascular obstruction, abscess, and glycogen-storage diseases.

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liver

1. a multilobed highly vascular reddish-brown glandular organ occupying most of the upper right part of the human abdominal cavity immediately below the diaphragm. It secretes bile, stores glycogen, detoxifies certain poisons, and plays an important part in the metabolism of carbohydrates, proteins, and fat, helping to maintain a correct balance of nutrients

2. the corresponding organ in animals

3. a reddish-brown colour, sometimes with a greyish tinge

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liver [′liv·ər]

(anatomy)

A large vascular gland in the body of vertebrates, consisting of a continuous parenchymal mass covered by a capsule; secretes bile, manufactures certain blood proteins and enzymes, and removes toxins from the systemic circulation.

(materials)

Intermediate layer of dark-colored, oily material formed by hydrolyzation of acid sludge from sulfuric acid treatment of petroleum oil; insoluble in weak acid and oil.

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Liver

A large gland found in all vertebrates. It consists of a continuous parenchymal mass arranged to form a system of walls through which venous blood emanating from the gut must pass. This strategic localization between nutrient-laden capillary beds and the general circulation is associated with hepatic regulation of metabolite levels in the blood through storage and mobilization mechanisms controlled by liver enzymes.

Function

The large size of the liver is matched by its functional complexity and involvement in a diverse array of regulatory mechanisms. The liver plays a key role in assuring carbohydrate homeostasis (dynamic steady-state conditions) by removing simple sugars from the general circulation after ingestion of food and storing them as glycogen. In the intervals between ingestion of food, liver glycogen is broken down. This process tends to maintain blood sugar levels between 80 and 100 mg per 100 ml of blood. Under conditions of prolonged fast, where glycogen stores are exhausted, the liver is capable of converting noncarbohydrate metabolites such as amino acids and fats into glucose to maintain blood sugar levels. The complex steps involved in maintaining carbohydrate metabolism are subject to endocrine control, with the liver serving as a particularly sensitive target organ of hormone regulators such as insulin. See Carbohydrate metabolism, Glucose, Glycogen, Insulin

The liver is key in the interconversion of many metabolites. It is a major site of production of fatty acids, triglycerides, phospholipids, ketone bodies, and cholesterol. Steroid hormones are degraded in the liver. See Cholesterol, Ketone, Lipid, Steroid

The liver is the sole source of such necessary constituents of the blood as fibrinogen, serum albumin, and cholinesterase. In the embryonic stage of most vertebrates the liver serves as the major manufacturing site of erythrocytes, a process known as erythropoiesis. The liver also removes toxins from the systemic circulation and degrades them, as well as excess hormones. Particulate material may be removed through a phagocytic action of specialized cells (Kupffer cells) lining the lumen of the hepatic “capillary spaces,” or sinusoids. In addition to the products which the liver delivers directly to the general circulation (endocrine function), it secretes bile through a duct system which, involving the gallbladder as a storage chamber, eventually passes into the duodenum (exocrine function). Bile functions as an emulsifier of fats to facilitate their digestion by fat-splitting lipases, and may also activate the lipase directly. See Gallbladder

Anatomy

The human liver is a massive wedge-shaped organ divided into a large right lobe and a smaller left lobe. Its anterior surface underlies the diaphragm. The upper portion of the liver is partially covered ventrally by the lungs, whereas the lower portion overhangs the stomach and intestine. The entire liver is covered by Glisson's capsule, an adherent membranous sheet of collagenous and elastic fibers.

Venous blood from the intestine, and to a lesser extent from spleen and stomach, converges upon a short broad vessel, called the hepatic portal vein, which enters the liver through a depression in the dorsocaudal surface termed the porta hepatis. There the hepatic portal vein divides into a short right branch and a longer left branch. These vessels then ramify into the small branches which actually penetrate the functional parenchymal mass as the inner tubes of the portal canals.

The hepatic artery also enters at the porta hepatis and ramifies into smaller branches, which flank the portal venules within the portal canals. The branches of the portal vein and hepatic artery then empty into sinusoids, which are major regions of hepatovascular exchange. They communicate with small branches of the hepatic veins and, through the hepatic vein, the blood is returned to the heart by way of the vena cava.

The tiny bile canaliculi, which lie between grooves in adjacent parenchymal cells, communicate with tiny intralobular bile ducts. These intralobular bile ducts empty into increasingly larger interlobular bile ducts which lie within the portal canals and make up the third element of the so-called portal triad.