Clinical Module Summary Notes - GIT

Clinical Module Summary Notes - GIT - Revised March 5 2004...

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Revised March 5, 2004 Gastrointestinal and Hepatobiliary Systems Liver/Spleen Anatomy Other than the skin, the liver is the largest organ in the body. It weighs ~ 1,500 – 1,700grams and is composed of four lobes, a right lobe (80% of the mass), a left (15%) and two small posterior lobes called the caudate and the quadrate lobes. The falciform ligament divides the liver more or less into right and left lobes (this may result in a notch appearing on the superior and inferior edges of the liver rather like placing a belt around a balloon, if the balloon expands it causes the belt to compress it ). Looking at the liver from the posterior view and lateral to the falciform ligament’s insertion (it wraps around the liver) we can delimit the caudate and quadrate lobes (these lie between the ligament, and the inferior vena cava and gallbladder). The gallbladder lies in a fossa between the right and quadrate lobes and may even be found within the liver tissue in the same area in rare cases. The Porta Hepatis (Latin for “door of the liver”) is a depression on the posterior medial aspect of the liver between the caudate and the quadrate lobes through which the hepatic artery, portal vein and common bile duct enter or leave the organ. The liver’s blood supply is derived from two separate sources and is essentially a “double” system (much like that of the lungs). 1
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Revised March 5, 2004 75 – 80% of the liver’s blood reaches the organ via the portal vein (this being venous blood derived from the superior mesenteric, splenic, gastric, pancreatic and gallbladder venous vasculature, and thus extremely rich in nutrients). The remaining 20 – 25% of the liver’s blood supply comes from the hepatic artery (branching off the abdominal aorta) which supplies the liver with its source of oxygenated blood. Physiology/Histology Hepatocytes (parenchymal cells) represent the bulk of the liver’s mass (about 85%) and make bile along with performing most of the organ’s functions. Kupffer cells: These line the liver sinusoids and remove cellular debris, phagocytize bacteria and blood-borne particulate materials. In a single pass through the liver the Kupffer cells are able to remove 95% of the sulphur colloid passing through it (but remember, not all of the injected dose passes through in the first passage of blood through the organ since the liver does not receive 100 % of the cardiac output). Factors influencing the rate of removal of the colloid by these cells include the rate and volume of blood flow through the liver, RES function (i.e., “healthy” versus “damaged”), physical characteristics of the particles (size, “quality” of the preparation, number of particles injected, particle surface charge, etc.). Spleen
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Clinical Module Summary Notes - GIT - Revised March 5 2004...

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