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Lecture 23 Notes.pdf

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Biological Sciences
Stephen Reid

1Lecture 23 Liver Function Digestion and Absorption of Carbohydrates Proteins and Lipids 1 Heme RecyclingAnother function of the liver is the recycling of old red blood cells and the components of haemoglobin Red blood cells have a lifespan of approximately 4550 days before they are recycled by being takenup into macrophages Within the macrophage haemoglobin is broken down into globin molecules which are further broken down into amino acids and released into the blood and the heme group The heme group is then converted into biliverdin and then reduced to bilirubin Bilirubin is released from the macrophage and binds with plasma albumin in the blood which transports it to the liver Within the liver bilirubin is conjugated with glucuronic acid to form a component of the bile which is then released into the small intestine Within the small intestine bilirubin is metabolized by gut bacteria to produce urobilinogen Urobilinogen can remain in the gut and become oxidized by gut bacteria to produce stercobilin which is voided in the feces and gives the brown colour to feces Urobilinogen can also leave the gut and enter the kidney where it is converted to urobilin which is voided in the urine and gives urine its amber colour 22 Absorption and Transport of Iron 2Iron Fe or heme groups ingested in food are transported into intestinal cells Within these cells 2 ion Within the intestinal absorptive heme is broken down by heme oxygenase to liberate the Fecells a protein named apoferritin binds iron and is converted into ferritin Each apoferritin protein can bind up to 4500 iron molecules The iron can remain in these cells or it can enter the blood and bind to a protein called apotransferrin During an iron deficiency the amount if iron that remains in the intestinal cells is reduced and iron transport out of the intestinal cells is increased If there is an excess of iron in the diet it is lost in the feces when the intestinal cells are shed Once apotransferrin binds iron it becomes diferric transferrin
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