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
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.... Medical Dictionary
A localised (focal) form of liver disease in all tropical/subtropical countries results from invasive Entamoeba histolytica infection (amoebic liver ‘abscess’); serology and imaging techniques assist in diagnosis. Hydatidosis also causes localised liver disease; one or more cysts usually involve the right lobe of the liver. Serological tests and imaging techniques are of value in diagnosis. Whilst surgery formerly constituted the sole method of management, prolonged courses of albendazole and/or praziquantel have now been shown to be e?ective; however, surgical intervention is still required in some cases.
Hepato-biliary disease is also a problem in many tropical/subtropical countries. In southeast Asia, Clonorchis sinensis and Opisthorchis viverini infections cause chronic biliary-tract infection, complicated by adenocarcinoma of the biliary system. Praziquantel is e?ective chemotherapy before advanced disease ensues. Fasciola hepatica (the liver ?uke) is a further hepato-biliary helminthic infection; treatment is with bithionol or triclabendazole, praziquantel being relatively ine?ective.... Medical Dictionary
In?ammation of the liver, or HEPATITIS, may occur as part of a generalised infection or may be a localised condition. Infectious hepatitis, which is the result of infection with a virus, is one of the most common forms. Many di?erent viruses can cause hepatitis, including that responsible for glandular fever (see MONONUCLEOSIS). Certain spirochaetes may also be the cause, particularly that responsible for LEPTOSPIROSIS, as can many drugs. Hepatitis may also occur if there is obstruction of the BILE DUCT, as by a gall-stone.
Cirrhosis of the liver A disorder caused by chronic damage to liver cells. The liver develops areas of ?brosis or scarring; in response, the remaining normal liver cells increase and form regeneration nodules. Those islands of normality, however, su?er from inadequate blood supply, thus adversely a?ecting liver function. Alcohol is the most common cause of cirrhosis in the United Kingdom and the USA, and the incidence of the disorder among women in the UK has recently risen sharply as a consequence of greater consumption of alcohol by young women in the latter decades of the 20th century. In Africa and many parts of Asia, infection with hepatitis B virus is a common cause. Certain drugs – for example, PARACETAMOL – may damage the liver if taken in excess. Unusual causes of cirrhosis include defects of the bile ducts, HAEMOCHROMATOSIS (raised iron absorption from the gut), CYSTIC FIBROSIS, cardiac cirrhosis (the result of heart failure causing circulatory congestion in the liver), and WILSON’S DISEASE (raised copper absorption).
Symptoms Some people with cirrhosis have no signs or symptoms and the disease may be diagnosed at a routine medical examination. Others may develop jaundice, OEDEMA (including ascites – ?uid in the abdomen), fever, confusion, HAEMATEMESIS (vomiting blood), loss of appetite and lethargy. On examination, cirrhotic patients often have an enlarged liver and/ or SPLEEN, and HYPERTENSION. Liver function tests, cholangiography (X-ray examination of the bile ducts) and biopsy of liver tissue will help to reach a diagnosis.
Treatment Nothing can be done to repair a cirrhosed organ, but the cause, if known, must be removed and further advance of the process thus prevented. In the case of the liver, a high-protein, high-carbohydrate, low-fat diet is given, supplemented by liver extract and vitamins B and K. The consumption of alcohol should be banned. In patients with liver failure and a poor prognosis, liver TRANSPLANTATION is worthwhile but only after careful consideration.
Abscess of the liver When an ABSCESS develops in the liver, it is usually a result of amoebic DYSENTERY, appearing sometimes late in the disease – even after the diarrhoea is cured (see below). It may also follow upon in?ammation of the liver due to other causes. In the case of an amoebic abscess, treatment consists of oral metronidazole.
Acute hepatic necrosis is a destructive and often fatal disease of the liver which is very rare. It may be due to chemical poisons, such as carbontetrachloride, chloroform, phosphorus and industrial solvents derived from benzene. It may also be the cause of death in cases of poisoning with fungi. Very occasionally, it may be a complication of acute infectious hepatitis.
Cancer of the liver is not uncommon, although it is rare for the disease to begin in the liver – the involvement of this organ being usually secondary to disease situated somewhere in the stomach or bowels. Cancer originating in the liver is more common in Asia and Africa. It usually arises in a ?brotic (or cirrhotic) liver and in carriers of the hepatitis B virus. There is great emaciation, which increases as the disease progresses. The liver is much enlarged, and its margin and surface are rough, being studded with hard cancer masses of varying size, which can often be felt through the abdominal wall. Pain may be present. Jaundice and oedema often appear.... Medical Dictionary