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Red blood cells.
Creation, function and destruction.
| Question | Answer |
|---|---|
| How much blood should a 70kg adult have and of what proportions? | 5L blood volume of which 40% cells and 60% plasma. |
| How many times more numerous are RBC than WBC? | x500- approximately 2.4x10^13. |
| How often do RBC need to replace? | RBC need to replace 1% per day to make up for expected lifespan of 100 days. |
| What does the biconcave disc and no nucleus allow the RBC to have? | Pliable, high surface area/volume. |
| What does the RBC contain inside it? | Bag of haemoglobin and enzymes for glycolysis- unable to divide or make new proteins. |
| How does the RBC prevent oxidation? | By maintaining membrane integrity. |
| What forms "blood islands"? | Embryological stem cells form blood islands in the yolk sac. |
| What is the cell pathway in the foetus? | Cells migrate to liver then spleen then bone marrow in foetus. |
| How does the distribution of bone marrow change as we grow? | At birth bone marrow is widely distributed, retreating to axial skeleton by adulthood. |
| What are the growth factors associated with RBCs? | Interleukin 3, erythropoietin, androgens and thyroxine. |
| What is in the stroma of bone marrow? | Fibroblasts, macrophages, endothelium and fat cells. |
| What is a reticulocyte? | An immature RBC. |
| What is reticulin? | Remnants of mRNA left once the nucleus of a maturing RBC has been extruded. Removed by the spleen in 1-2 days. |
| What can reticulocyte numbers be used to measure? | A useful measure of marrow response to anaemia or treatment. |
| What can be used to stain reticulocytes? | New methylene blue on slide. |
| How much iron to adults have and where is most of it? | 3000-5000mg of iron of which 2/3 is in haemoglobin. |
| Where is Fe++ transported to? | Transported into duodenal enterocytes. |
| What regulates iron absorption and release? | Hepcidin regulates iron absorption and release from macrophages- increased in inflammatory disease hence less available iron. |
| Is there a mechanism to excrete iron? | No. |
| How can humans lose iron? | Menstrual loss, minor trauma, GI, blood sampling and very small amounts in urine and skin shedding. |
| What is the function of transferrin? | Glycoprotein found in the blood plasma, that is capable of binding iron and thus acts as a carrier of iron in the bloodstream. |
| What is the function of ferritin? | An iron-protein complex that is one of the forms of which iron is stored in the tissues (insoluble). |
| What is the daily requirement of folic acid/folate? | 0.1mg. |
| Where is folate absorbed? | Upper small bowel. |
| Where is folate stored and how much is stored? | In the liver (10-20mg). |
| What is folate and its function? | B vitamin that is important in the synthesis of nucleic acids. |
| What is the daily requirement of B12/cobalamin? | 1 microgram, all from animal derived products. |
| What produces the "intrinsic factor" and what does it do? | Gastric parietal cells. It binds to B12. |
| Where is B12 absorbed? | In the terminal ileum. |
| What is B12 transported on? | Transcobalamin II via portal circulation to the liver. |
| Why do RBC need B12? | Required in change from 5 methyl tetrahydrofolate (THF) to THF. Further change to 5,10 methelene THF which catalyses conversion of uridine to thymidine. |
| What is erythropoietin? | A hormone secreted by certain cells in the kidney in response to a reduction in the amount of oxygen reaching the tissues. |
| What controls erythropoiesis? | Erythropoietin increases the rate of RBC production (erythropoiesis) and is the mechanism which controls erythropoiesis. |
| What is the structure of erythropoietin? | Glycosylated 165 amino acid protein- renal 90%, liver 10%. |
| What are the medical uses of erythropoietin? | Useful recombinant drug for renal anaemia and myelodysplasia (increase drive to erythropoiesis). |
| What switches on production of erythropoietin? | Tissue hypoxia or anaemia, high altitude and epo producing tumours e.g. renal. |
| What is hypoxia? | Deficiency of oxygen in the tissues. |
| In terms of hormones, what happens at low oxygen levels in tissues? | mRNA for epo is increased and epo is produced. |
| What is spherocytosis? | The presence in the blood of abnormally shaped red cells. |
| What does haemoglobin need to form? | 2 alpha (zeta in foetus) chains and 2 beta chains. |
| What chromosome codes for the alpha chains? | Chromosome 16. |
| What chromosome codes for the beta chains? | chromosome 11. |
| What is Thalassaemia? | An inherited defect in globin chain production. |
| What causes sickle cells disease? | One amino acid change in the beta chain. |
| Why do RBCs need enzymes? | For a glycolytic pathway ending with lactate and pyruvate providing energy. |
| What is energy needed for in RBCs? | Maintain membrane integrity, prevent oxidation of enzymes and Fe++ and to maintain gradients of K+ and Ca++. |
| What would cause a oxygen dissociation curve to shift to the right? | Acidosis and increased temperature will cause a right shift and hence deliver more O2 to tissues. |
| What does 2,3 diphosphoglycerate do? | An intermediate step in glycolysis produces a right shift of O2 dissociation curve hence more released in the tissues. |
| When is 2,3 DPG increased? | Exercise, anaemia and high altitude. |
| What is myoglobin? | An iron-containing protein found in muscle cells- acts as a store for O2 for immediate use. One haem unit, one globin chain. |
| What is the normal blood pH? | 7.35-7.45. |
| Why is acidosis important for enzymes? | They work optimally at physiological pH. |
| What happens to cell membranes in acidosis? | They become leaky. |
| What happens to neurones in acidosis? | Become less able to transmit in acidosis- hyperactive in alkalosis. |
| What is the bicarbonate buffer equation? | CO2+H2O--->H2CO3---->(H+)+HCO3- |
| What happens to the buffer equation is there is a decrease in pH? | A decrease in pH will drive the equation to the left. |
| What are the buffer equations catalysed by? | Carbonic anhydrase. |
| What is the buffer capacity of haemoglobin? | 30%. |
| In terms of H+ what happens to haemoglobin after it loses its oxygen? | It combines with H+ and the low pH decreases haemoglobin affinity for O2. |
| What happens to the RBC as it ages? | Membrane becomes more rigid. Loss of glycolytic enzymes. Neoantigents exposed on cell surface. |
| What happens to old RBCs? | Some RBC lost from GI tract/into soft tissues/menstrual loss. Some RBC destroyed within body. |
| What "mops up" free haemoglobin? | Haptoglobin- cleared by the liver. Any excess can appear in urine. |
| What happens to the globin once the RBC is destroyed? | Globin chains broken into AAs. |
| What happens to the iron once the RBC is destroyed? | Iron bound to transferrin and returned to macrophages. |
| What happens to the porphyrin ring once the RBC is destroyed? | Becomes bilirubin- bound to albumin and "conjugated" to glucuronide and then excreted in the bile. |
Created by:
robertspedding
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