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liver - Liver Gross Anatomy Weighs 1.2-1.5 kg and is...

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Liver: Gross Anatomy ? Weighs 1.2 -1.5 kg and is largest organ in the body ? Located beneath the diaphragm in right upper quadrant of abdomen and is protected by the ribs ? Divided into left and right anatomical lobes ? Supplied by left and right branches of the portal vein and hepatic artery ? Venous drainage is into the hepatic veins, whereas biliary drainage is into the left and right hepatic ducts ? Thin connective tissue (Glisson’s capsule) covers entire liver surface ? Connective tissue provides an internal supportive framework for the liver parenchyma; branches to ensheath vessels and nerves, and subdivides the paraenchyma into lobules Liver: Hepatic Vascular System ? The circulatory system of the liver is unlike that seen in any other organ. ? Of great importance is the fact that a majority of the liver's blood supply is venous blood. ? Roughly 75% of the blood entering the liver is venous blood from the portal vein. Importantly, all of the venous blood returning from the small intestine, stomach, pancreas and spleen converges into the portal vein. ? One consequence of this is that the liver gets "first pickings" of everything absorbed in the small intestine, which is where virtually all nutrients are absorbed. ? The remaining 25% of the blood supply to the liver is arterial blood from the hepatic artery. Liver: Hepatic Vascular System ? Terminal branches of the hepatic portal vein and hepatic artery empty together and mix as they enter sinusoids in the liver. ? Sinusoids are distensible vascular channels lined with highly fenestrated or "holey" endothelial cells (Kupffer cells) and bounded circumferentially by hepatocytes. ? As blood flows through the sinusoids, a considerable amount of interstitial fluid is filtered into the space between endothelium and hepatocytes (the "space of Disse"), across which the transfer of nutrients and waste products from the blood and liver cells occurs. ? Blood flows through the sinusoids and empties into the central vein of each lobule. ? Central veins coalesce into hepatic veins, which leave the liver and empty into the vena cava. Liver: Architecture of HepaticTissue ? The liver is covered with a connective tissue capsule that branches and extends throughout the substance of the liver as septae. ? This connective tissue tree provides a scaffolding of support and the highway which along which afferent blood vessels, lymphatic vessels and bile ducts traverse the liver. ? Additionally, the sheets of connective tissue divide the parenchyma of the liver into very small units called lobules. ? The hepatic lobule is the structural unit of the liver. ? It consists of a roughly hexagonal arrangement of plates of hepatocytes radiating
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outward from a central vein in the centre. ? At the vertices of the lobule are regularly distributed portal triads, containing a bile duct and a terminal branch of the hepatic artery and portal vein.
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