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blood 2-2,3

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McGill University
PHGY 209
Ann Wechsler

RBC has no nucleus nor any subcellular organelles, so it cannot regenerate. The life span of a red blood cell is 120 days. During that time, each red blood cell travels the equivalent of 300 miles. Nothing can prolong the lifespan of a red blood cell. Old RBCs are recognized and removed by macrophages. The macrophages digests the RBC by extending its pseudopod around the RBC. RBC gets digested, broken up, and bits are expelled out of the macrophage. The lifespan of a red blood cell: RBC are synthesized in the bone marrow of an adult. It is released into circulation and survives for 120 days. Old RBCs are broken up or picked up by macrophages (and contents are released). Once the hemoglobin is released, it is broken up into various components. The globin part is broken up to amino acids which are used by the body to synthesize other proteins. The iron is released and most of it is conserved in the body. Iron by itself is toxic, so it becomes associated with a plasma protein called transferrin. It is then transferred to be stored in a protein called ferritin. The storage takes place in the liver, spleen, and gut. Most iron associated with transferrin is returned back to the bone marrow. If you need more iron, the ferritin will transfer more iron to the bone marrow. Heme is broken down and released into the circulation as bilirubin (this is done by the macrophage). Bilirubin is a product that contains an organic yellow-ish pigment molecule. It circulates in the plasma and gets picked up by the liver and undergoes additional modification. It is then released by the liver in the bile. In the intestinal tract, it will go under more modification in the colon, and then excreted from the body. Bilirubin gives bile the yellow color. There is 1 miligram of bilirubin per deci-litre in plasma. Sometimes the concentration of bilirubin is greater, and plasma becomes dark yellow can deposit into the skin. Excess production of bilirubin can lead to jaundice. Many newborn babies have jaundice. If there is too much bilirubin in the plasma, the pigment can deposit in the brain. There is a treatment, just expose the baby to a certain wavelength of blue light, and it converts the bilirubin in blood from lipid soluble, to water soluble bilirubin, which it can then be readily excreted from the body. Knowing how bilirubin is produced and how it is removed from the body, under what circumstances would one develop jaundice? One, liver damage. Two, excessive hemolysis, some forms of anemia in which the RBC gets broken up in bloodstream, releasing hemoglobin and heme will be broken down to bilirubin. Hemolysis is the release of contents of RBC. Three, bile duct obstruction. If there is a gall stone or tumour that blocks the path, bilirubin would accumulate in the circulation. Lastly, polycythemia, the excessive production of RBCs. RBC production is equal to destruction. When production is greater than destruction, it leads to polycythemia. When production is less than destruction, it leads to anemia. The Hematocrit can be used to evaluate the status of blood cells. The Hematocrit represents the proportion of blood made up by RBC. Normal Ht is 45%. A decrease in Ht means a decrease in RBC. However there are situations where the Ht does not really represent the total number of RBC in the body. If the Ht is 70% it can mean that there are more RBCs (which leads to polycythemia) but it could also be that someone is dehydrated, so the plasma volume is less. If the Ht is 30% it can mean anemia but a low Ht could also be due to fluid retention (maybe kidney damage). Just remember, is it a change in plasma volume, or actually a change in the number of RBCs? You can have relative polycythemia or absolute polycythemia. Relative polycythemia is due to a decrease in plasma volume (it can look like polycythemia). Absolute polycythemia is physiological or pathological. If it is physiology, that means it is in response to an increased oxygen need or a decreased oxygen availability. At high altitudes one will start producing more RBC, increased physical activity, chronic lung disease, or heavy smoking. If it is pathological, there are tumours in the cells producing erythropoietin due to unregulated production by the bone marrow. Polycythemia is a rare condition though. The problem with polycythemia is that it increases blood viscosity – it makes it harder for the heart to push the blood (which can cause high blood pressure). Blood flow is also slower and can lead to blood clots. Anemia is not a disease, it is a manifestation that something is wrong. Either production is too low or destruction is too high. There is a decrease in the oxygen-carrying capacity of the blood. The morphologic classification of anemia is microcytic, normocytic, and macrocytic. This is the size of the RBC. The hemoglobin content is normochromic and hypochromic (<33%). Anemia can be caused by diminished production, ineffective maturation, or increased destruction. Let’s start with diminished production. Diminished production can happen in the abnormal site, abnormal stimulus or inadequate raw material. In abnormal site it can be called aplastic or hypoplastic anemia, when the bone marrow fails to produce RBC). These reasons are unknown but scientists think it may be due to exposure to radiation or chemicals or drugs. The classification of this anemia is normocytic and normochromic. Again, abnormal site anemia is normocytic and normochromic. Abnormal stimulus is due to stimulation failure. This can be caused by renal disease. What do you do if someone has a kidney problem? You give them erythropoietin because it will stimulate the bone marrow direction to produce more RBC. Classification of abnormal stimulus anemia is normocytic and normochromic. Inadequate raw materials is an iron deficiency anemia, which is the most common type of anemia. This inadequate supply can be due to failure to absorb iron from the diet (an abnormality of the gut perhaps), or a dietary deficiency, or a loss of iron because of hemorrhage). Babies, adolescence, and pregnant women are most susceptible
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