n. see bile pigments.
Form The liver is divided into four lobes, the greatest part being the right lobe, with a small left lobe, while the quadrate and caudate lobes are two small divisions on the back and undersurface. Around the middle of the undersurface, towards the back, a transverse ?ssure (the porta hepatis) is placed, by which the hepatic artery and portal vein carry blood into the liver, and the right and left hepatic ducts emerge, carrying o? the BILE formed in the liver to the GALL-BLADDER attached under the right lobe, where it is stored.
Position Occupying the right-hand upper part of the abdominal cavity, the liver is separated from the right lung by the DIAPHRAGM and the pleural membrane (see PLEURA). It rests on various abdominal organs, chie?y the right of the two KIDNEYS, the suprarenal gland (see ADRENAL GLANDS), the large INTESTINE, the DUODENUM and the STOMACH.
Vessels The blood supply di?ers from that of the rest of the body, in that the blood collected from the stomach and bowels into the PORTAL VEIN does not pass directly to the heart, but is ?rst distributed to the liver, where it breaks up into capillary vessels. As a result, some harmful substances are ?ltered from the bloodstream and destroyed, while various constituents of the food are stored in the liver for use in the body’s metabolic processes. The liver also receives the large hepatic artery from the coeliac axis. After circulating through capillaries, the blood from both sources is collected into the hepatic veins, which pass directly from the back surface of the liver into the inferior vena cava.
Minute structure The liver is enveloped in a capsule of ?brous tissue – Glisson’s capsule – from which strands run along the vessels and penetrate deep into the organ, binding it together. Subdivisions of the hepatic artery, portal vein, and bile duct lie alongside each other, ?nally forming the interlobular vessels,
which lie between the lobules of which the whole gland is built up. Each is about the size of a pin’s head and forms a complete secreting unit; the liver is built up of hundreds of thousands of such lobules. These contain small vessels, capillaries, or sinusoids, lined with stellate KUPFFER CELLS, which run into the centre of the lobule, where they empty into a small central vein. These lobular veins ultimately empty into the hepatic veins. Between these capillaries lie rows of large liver cells in which metabolic activity occurs. Fine bile capillaries collect the bile from the cells and discharge it into the bile ducts lying along the margins of the lobules. Liver cells are among the largest in the body, each containing one or two large round nuclei. The cells frequently contain droplets of fat or granules of GLYCOGEN – that is, animal starch.
Functions The liver is, in e?ect, a large chemical factory and the heat this produces contributes to the general warming of the body. The liver secretes bile, the chief constituents of which are the bile salts (sodium glycocholate and taurocholate), the bile pigments (BILIRUBIN and biliverdin), CHOLESTEROL, and LECITHIN. These bile salts are collected and formed in the liver and are eventually converted into the bile acids. The bile pigments are the iron-free and globin-free remnant of HAEMOGLOBIN, formed in the Kup?er cells of the liver. (They can also be formed in the spleen, lymph glands, bone marrow and connective tissues.) Bile therefore serves several purposes: it excretes pigment, the breakdown products of old red blood cells; the bile salts increase fat absorption and activate pancreatic lipase, thus aiding the digestion of fat; and bile is also necessary for the absorption of vitamins D and E.
The other important functions of the liver are as follows:
In the EMBRYO it forms red blood cells, while the adult liver stores vitamin B12, necessary for the proper functioning of the bone marrow in the manufacture of red cells.
It manufactures FIBRINOGEN, ALBUMINS and GLOBULIN from the blood.
It stores IRON and copper, necessary for the manufacture of red cells.
It produces HEPARIN, and – with the aid of vitamin K – PROTHROMBIN.
Its Kup?er cells form an important part of the RETICULO-ENDOTHELIAL SYSTEM, which breaks down red cells and probably manufactures ANTIBODIES.
Noxious products made in the intestine and absorbed into the blood are detoxicated in the liver.
It stores carbohydrate in the form of glycogen, maintaining a two-way process: glucose
glycogen.
CAROTENE, a plant pigment, is converted to vitamin A, and B vitamins are stored.
It splits up AMINO ACIDS and manufactures UREA and uric acids.
It plays an essential role in the storage and metabolism of FAT.... liver
The waste products in bile include the pigments bilirubin and biliverdin, which give bile its greenish-brown colour; bile salts, which aid in the breakdown and absorption of fats; and cholesterol. Bile passes out of the liver through the bile ducts and is then concentrated and stored in the gallbladder. After a meal, bile is expelled and enters the duodenum (the first section of the small intestine) via the common bile duct. Most of the bile salts are later reabsorbed into the bloodstream to be recycled by the liver into bile. Bile pigments are excreted in the faeces. (See also biliary system; colestyramine.)
bile duct Any of the ducts by which bile is carried from the liver, first to the gallbladder and then to the duodenum (the first section of the small intestine). The bile duct system forms a network of tubular canals. Canaliculi (small canals) surround the liver cells and collect the bile. The canaliculi join together to form ducts of increasing size. The ducts emerge from the liver as the 2 hepatic ducts, which join within or just outside the liver to form the common hepatic duct. The cystic duct branches off to the gallbladder; from this point the common hepatic duct becomes the common bile duct and leads into the duodenum.
(See also biliary system.)
bile duct cancer See cholangiocarcinoma. bile duct obstruction A blockage or constriction of a bile duct (see biliary system). Bile duct obstruction results in accumulation of bile in the liver (cholestasis) and jaundice due to a buildup of bilirubin in the blood. Prolonged obstruction of the bile duct can lead to secondary biliary cirrhosis. The most common cause of obstruction is gallstones. Other causes include a tumour affecting the pancreas (see pancreas, cancer of), where the bile duct passes through it, or cancer that has spread from elsewhere in the body. Cholangiocarcinoma (cancer of the bile ducts) is a very rare cause of blockage. Bile duc.
obstruction is a rare side effect of certain drugs. It may also be caused by cholangitis (inflammation of the bile ducts), trauma (such as injury during surgery), and rarely by flukes or worms.
Bile duct obstruction causes “obstructive” jaundice, which is characterized by pale-coloured faeces, dark urine, and a yellow skin colour.
There may also be itching.
Other symptoms may include abdominal pain (with gallstones) or weight loss (with cancer).
Treatment depends on the cause, but surgery may be necessary.
Gallstones may be removed with an endoscope (see ERCP).... bile
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