Liver 2009 (2) - 1 Liver, Gallbladder, Pancreas - 2010 The...

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1 Liver, Gallbladder, Pancreas - 2010 The liver and pancreas are two major glands that are associated with the digestive tract. Other glands, the salivary glands, will be discussed later. The liver is the largest internal organ located in the right upper quadrant of the abdominal cavity, protected by the right lower rib cage. It is the largest exocrine gland in the body, but like the pancreas, it is also an endocrine gland. Most of the cells (about 70%) found in the liver are hepatocytes (hepaticus is L. for liver; hepar is Gk. for liver). Hepatocytes are the most versatile cells in our body capable of an unbelievable variety of functions including synthesis, metabolism of sugars, amino acids and fats, secretion, storage of glycogen, vitamins, etc. They make thousand of proteins, lipoproteins, including the albumin and clotting factors of blood. Bile is the major exocrine product. Hepatocytes have extensively developed intracellular organelles: ER, RER, mitochondria, and usually several Golgi complexes. The liver is surrounded by a capsule (Glisson’s capsule) consisting of a little CT covered with mesothelium (CT covered with a mesothelium = a serosa). This serosa continues over the peritoneal surface of the gallbladder. The porta (L. for gate) hepatis (or hilum) is the area underneath and somewhat posterior on the liver where blood vessels enter. It is also where the common bile duct leaves the liver. Through the porta hepatis, CT tissue passes to divide the liver into lobules. Before discussing the histology and lobular structure of the liver, we will look at the blood supply to the liver. This is unique among all our organs. The liver has a dual blood supply: the portal vein and the hepatic artery. What is a portal system? Usually blood flows from artery to a capillary to a vein and then back to the heart. In a portal system blood flows from artery to capillary to vein (in the digestive tract, the portal vein) and then into another capillary bed (the sinusoids of the liver). From the sinusoids, the venous blood drains into the central veins, then the hepatic veins which enter the inferior vena cava and hence back to the right side of the heart. So, a portal system is simply one capillary bed draining via a connecting vein into another capillary bed. The hepatic portal system is the largest portal system in the body. The portal vein itself is formed by the coalescence of the superior and inferior mesenteric veins along with splenic vein. (Look at the picture of the portal vein I sent you). We will see another very important portal system in the pituitary glands. 75% of the blood supply to the liver comes from the portal vein . The venous blood in the portal vein is rich in goodies (nutrients taken up in the small intestine) but it is poor in oxygen. Oxygen is supplied to the liver by the hepatic artery which supplies 25% of the blood to the liver. These vessels, the portal vein and the hepatic artery, enter
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2 through the porta hepatis (hilum of liver, if you are more familiar with that term) and
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Liver 2009 (2) - 1 Liver, Gallbladder, Pancreas - 2010 The...

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