Gastrointestinal Nursing.pdf

The Liver 107Figure 7.1 Position of the liver in the abdomen. Reproduced with permission fromHinchliff et al. (1996).The liver is composed of highly metabolically active cells called hepatocytesand these are arranged in lobules, with the gross structure of the liver composedof two lobes. Being metabolically active means that the liver requiresan adequate supply of oxygenated blood, which is provided by the hepaticartery. Waste substances generated in the liver are removed to the generalcirculation for excretion by the hepatic vein. However, the liver is unique inhaving two blood supplies and the second blood supply comes via the hepaticportal veins, which take nutrients from the gastrointestinal tract to the liver.All of the above – the hepatocytes, the hepatic arterial blood, the hepaticvenous blood and the portal blood – are in close proximity in the liver andat a microscopic level in the lobules where arterioles and interlobular veinsbring oxygenated blood and nutrients, respectively, from the gastrointestinaltract to the hepatocytes. At the centre of the lobules there is a central interlobularvein, which removes deoxygenated blood and waste products to the venouscirculation. Separated from the blood by hepatocytes are the bile canaliculi,which collect bile. Bile is composed of the breakdown products of red cells,which are processed in the liver. Bile is composed of water, bile pigments andbile salts. About a litre of bile is produced daily and this trickles down the bilecanaliculi into the hepatic ducts, to the common hepatic duct and into the gallbladder via the cystic duct. The function of the gall bladder is to concentratebile by the removal of water; this occurs in the presence of fatty foods in theduodenum, which stimulates the release of the hormone cholecystokinin.Cholecystokinin leads to contraction of the gall bladder and the relaxationof the sphincter of Oddi and the release of bile into the duodenum via theampulla of Vater.